CA1185314A - Connector for electromagnetic impulse suppression - Google Patents

Abstract

CONNECTOR FOR ELECTROMAGNETIC IMPULSE SUPPRESSION

ABSTRACT OF THE DISCLOSURE
A connector is provided for the suppression of electromagnetic impulses traveling along a radio frequency cable. Paired first and second electrical connectors are provided for being operatively interposed along the signal cable. A spacer or mounting device is provided for electrically coupling the primary conductors and secondary conductors of one connector to their counterparts in the other paired connector.
discharge device or tube having a known breakdown voltage and a known capacitance is coupled between the first and second conductors. The inductance of the elements comprising the mounting device is determined such that this inductance interacts with the capacitance of the discharge device and other stray capacitance of the combination thereof in order to produce a desired characteristic impedance, which is generally preferred to be equal to the characteristic impedance of the radio frequency signal cable, whereby the suppressor will dissipate electrical surges while representing a low standing wave ratio to radio frequency energy being transmitted along the radio frequency signal cable.

Description

~0P~4~2 Q~N ~ ~53~4 ~QNNECTOR FOi~ ELE~T~OM~GNETI~ I~iPULSE SUPP~ESSION

B~CKGROUNi~ OF THE INVENTION

I. FIEL~ OF THE IN~ENTION

The present invention relates to protective devices for suppressing short duration, high energy impulses, such a~
lightning stri~es! which may occur along coaxial cables or other HF, ~HF or UHF transmission lines. ~iore particularly, the invention rel~tes to the use of a discharge tube or device in combin~tion with connectors for being inserted in series with the transmission line.

Il. ~ESCi~lPTlON OF THi- P~IO~ ~RT

The use of vacuum tubes in prior radio frequency transmitting and ræceiving equipment made them somewhat tolerant to nearby lightning stri~es ~ince the brea~down voltage of the tubes was relatively high and ~ince the tubes would typically not be damaged unless there was a direct lightning stri~e on the ~ntenna or the feedline. Qn the other hand, recent advances in solid state design technolo~y have ~llowed tr~nsistors to replace tu~es in most applications. The problem~ of surge protection or lightning stri~es for transistori~ed receivers or transmitters is especially troublesome in view of the low brea~down voltages for typical solid state devices. Once this low ~reai<down voltage has been exceeded, the solid state device is no longer oper~tive and must be replaced.
Solid st~te devices of this type are presently ~eing widely utilized in television receivers, televi 5 ion receiving convertors, ca~le television distribution and ~mplification ~

~ ~ ~iS3~4~

systems and other similar ~HF and UHF radio frequency systems.
The proliferation of solid state devices in systems such as these substantially increases the probability o-f a large number of cc,mplex and exper,sive electronic devices beinc~ destroyecl by one well-placed lightning strike.
The cost of the lightning or surge protection has become more economical in view of the large cost of repairing this equipment. This cost factor becomes even more economic~l when the lightning or surge protection device can withstand multiple lightning stri~es of reasonable intensity without the necessity of replacing the protective device or without distruction of any equipment attached thereto. However7 these economies of lightning protection are not acceptable if the performance of the system in which the lightning protection device is used is degraded by the insertion of the protection device. Transmitting systems are of the gre~test interest in this regard since the insertion loss and ~SWR along the transmission line are somewhat critical at VHF and UHF frequencies.
The prior art has many examples of electromagnetic impul~e protection devices for radio frequency transmission lines. The earliest devices employed a groundincJ strap which merely grounded both sections of the transmis~ion line in ordær to reduce the likelihood of static electricity buildup and the concomitant likelihood of a lightning strike. This solution is obviously unacceptable when continuous transmission of radio frequency energy is required.
Later impulse protection systems employed air gaps in order to allow the lightning or impulse signal to arc across the gap and thereby travel to ground. One example of a device of this type employing air gaps is described in Cushman in U.S. Patent 2S~22,~13. This device is presently being mar~eted under the trademark SLITZ-BUG. Devices o4 this type suffer from several different problems. First, since the device exists in the ambient atmosphere, any arc drawn from one of the spark gaps .

3~
~ill cause severe vaporization or oxidation of the gap electrodes. Thi 5 de~redation of the electrodes could substantially increase the subsequent gap firing voltages above the level tolerated by solid state devices. In the extreme, the oxidation or vaporization of the electrodes can render the device useless after one or two lightning stri~es. Since there is no external indication of the occurrence of such a lightning stri~e or the uselessness of the spar~ gaps internal to the device, the system is left completely unprotected while the device outwardly appears to be operative. Frequent disassembly and inspection of the gaps may be re~uired. Secondly, the large air gaps utilized in devices of this type are not suitable for transistorized e~uipment. Srea~down voltages of 1500 to ~000 volts are typically required in order to r~use ~n arc to occur between the electrode elements across the air gap~ Transistors often will be destroyed by volt~ge well below this level.
Nelson, in U.S. Patent 3 ! 274,447 3 discloses a co~xial connector of the type employing an internal gap for allowin4 the impulse to arc to ground potenti~ evices of this type9 while mc,re suitable for insertion into coaxial transmission lines, suffer from the same basic oxidation and vapori~ation problems as described with regard to U.S. Patent ~ p~13.
Other inventors h~ve concentrated on combining protection for radio fre~uency transmission lines with protection for AC
electrical supply protection. Sim~at, in U.S~ Patent 4,050,0~, assigned to the Tll Corporation of Lindenhurst, N.Y., is an example of a gas-filled tube being utilized to shunt the electrical energy from a primary electrical conductor to ground in order to protect the sensitive electronic 501 id state devices coupled to the transmission line. This particular de~ice also protects the ~C power lines feeding the receiver or transmitter from an electrical surge. ~evices of this type are not suitablæ

for use at high frequencies because, contrary to the te~chings of Simokat, no precautions have been taken to assure proper ~ ~53~L
impedance matching and to minimi~e the insertion 1055 of the device in the ~HF or the UHF transmission line~. Alsot the device as dæscribed by Simo~at i 5 primarily related to receiving applications and would not be suitable for applications involving transmission of radio frequency power. Furthermore, the inherent design of the device as disclosed by Simo~at is not suitable for impedance matching for proper operation at UHF
frequencies (a~ ~sed herein UHF frequencies will refer to the frequencies abo~e 40~ MHz and below 3,000 MHz).

The Simo~at g~s-filled tube impulse protection device is widely used on low frequency transmission lines such as power lines9 telephone lines, low speed data lines, etc. However, the use of these gas-filled tubes has not been generally successful on radio frequency transmission lines without a substantial degredation of the characteristic impedance of the sicJnal transmission line. This impedance anomaly causes the occurrence of st~nding waves (VSWR~, signal los~es5 and group ph~se delays which are highlY undesirable and detrimental to the proper functioning of most communications systems.
Martzlogg, in U.S. Patent 3~ ,111, assigned to the General Electric Company, attac~s the surge protection problem by providin~ a coaxial-type connector which employs a polycrystalline varistor for surge protection. ~ spring is provided to compress the varistor into electrical contact with ground potential. The spring is designed to form a resonant circuit in conjunction with the conductors within the connector.
This spring acts as an inductor which is a low impedance to the relative low frequencies of the impulse, but is a relatively high impedance at higher frequencies. ~esigns of this type typically are suitable only for use in the HF or ~HF region (below 50-100 MHz). The device is typically not useable at frequencies below the self resonant frequencY of the coil t and the multiple higher resonant frequencies of the coil and various internal capacitances indicate that, at least at the higher ~requencies, the insertion 1 05S will sub~tantially increase an~
the attentuation curve (as a function of frequencY) will be extremely uneven. The reactance of the coil and its related circuit will cause a relatively high ~SWR to occur on the line at eværy series resonant point. These points occur due to stray capacitances. The insertion losses of devices of thi~ type can be substantial at ~HF frequencies. Furthermore ? the power handling capability of varistors of this type are highly suspect. Devices of this type are usually used only for receiving applications and aræ not suitable for high power transmitter applications.
Winters, in U.S. Patent 3,777,~1~, discloses a coaxial connector device which defines an internal caVitY. ~ plurality of semiconductor wafers employing silicon junction avalance-type diodes are carried within the cavity. The occurrence of a large voltacJe impulse along the center condu tor of the device will be short~ed to ground (the outside braid of the coaxial connector cable) when the impulse voltage exceeds the threshold voltage of the 5 ilicon junction avalanche diodes. ~valanche diodes of this type are not well suited for high power transmission applications hecause no effort has been made to ma~e the apparent impedance of the unit completely tr~nsparent to all ~F
energies by including it as an integral section of transmission line. Furthermore, the power handling capabilities of the avalanche Jiodes are somewhat limited, with an 8 microsecond rise and a ~0 microsecond delay time being typical. Devices of this type are usually limited to receive only applications and there~ore impedance matching at the higher frequencies is not ~s critical.

The capacitive effect~ of the diodes limit the design of this protection device to high frequency applications. In order to use it for the transmissic;n of ~F energy, the number of diodes must be increased in the series configuration in order to increase the series avalanche voltage. This reduces the current ~ ~ ~53~
~andling capabilities of the device since each diode ha~ a substantial serie~ resistar,ce value. ~ more diodes are added in series~ the total 'on" resistance value increases. If the brea~down voltacIe of each individual diode is increased to handle more power, the size of the diode must also increase as the junction area increases. This alsc, causes an increase in the "off" capacitance for each diode, which will limit the high frequency usage of the deviceO The diode h~s a very fa~t turn-on time, about 10 better than a gas tube, but it has smaller current handlin~ capabilitie 5 and p~wer di 55 ipation factors.
McNatt~ in U.S. P~tent ~,~S6,744, discloses a coaxial connector device which employs a series connected fuse in the primary circuit conductor. ~ cho~e c,r discreet inductor is coupled from the primary or center circuit conductor to the outside shield conductor. The inventor indicates thRt this cho~e will typically limit the use of this device to frequencies in th~e Z5-30 MHz r~n~e, which is at the very lowest edge of the VHF frequency bands. ~ device of thi 5 type would not be suitable for use at higher frequencies ~such as above 5~-10~
megacycles~ and would not be suitable for use with high powered transmitters.
~ arious other lightnin~ or surge protection devices are descri~ed by Fuller in U.S. Patent ?,896,123, Braumm in U.S.
Patent 3,450,~23, J~c~son in U.S. Patent l,1~4,1~5, P~cent in U.S. Patent l,527,525, Fin~el in U.S. Patent 2,654,S57, Grassnic~ in U.S. Patent 2,237,426, Epstein in U.S. Patent Z,277,2l6, Boylan in U.S. Patent 2,~57,ll0, Klostermann in U.S.
Patent 2,666,~0~, ~nd Craddoc~ in U.S. Patent 1,S~2,567. ~ari OU5 other lightning protection and surge protection devices are disclc,sed by Clar~ in U.S. Patent ~,~34,175 and Brown in U.S.

Patent 3,S40,78l.
Gilberts, in U.S. Patent 4,15S,S6~, discloses the use of a gas discharge tube in a device for protectirlg telephone lines ~ ~ ~S3~
from electrical impul~e~ or lightning stri~es. Lunclsgaard, in U.S. Patent 4,142,220, also discloses the use of a gas discharge tube for protecting telephone lines. The preent in~entor has examined both of the~e references and doe6 not believe that either of the references jc suitable for use at UHF frequencies where impedance matching and inser~ion lo~ses are of critical importance. Neither of these devices teache~ the use of an impedance matching technique where~y the lumped inductance~ and capacitances, when ta~en together, represent the same characteristic impedance of the connector and surge protector as compared to the coaxia7 feed lines.
In contrast to the prior art, the present invention relates to a connector of the type which may ~e inserted into a length of coaxial radio frequency cablel or other HF, ~HF or UHF
transmis~ion line, for controlling and dis~ipating the surge energy ~such as lightning~ traveling from the antenna side toward the receiverftran~mitter side, while not presenting a high ~SWR or insertion loss when viewed from the transmitter end toward the antenna end o4 the line. The capacitance of the discharge device used in the circuit, and other stray or distri~uted capacitancesl are cau~ed t~ interact with distributed inductive reactance so that the characteristic impedance of the connector, when viewed as a lumped element circuit, will correspond to the characteristic impedance of the transmission line. Thus, the connector will be transparent to the transmitted RF signal, but will ~e effective in dis~ipating or shunting the electrical impulse traveling down the line.

SUMM~Y OF THE INVENTION

This invention relates to an electrical surge suppre~sor for dissipating power surges along a radio frequency signal cable of the type having a primary and a 6econdary conductor and a ~nown characteristic impedance. The suppressor includes paired first and second electrical connectors~ each having ~ ~ ~5~
primary and secondary conductors for being operatively interposed along the primary and secondary conductors of the radio frequency signal cable. Q discharge device, typically a gas discharge tuke~ i 5 provided havinc~ a ~nown brea~down voltage and a ~nown capacitance between first and a second sections thereof. ~ mounting brac~et is provided for electrically coupling the first section of the ga5 discharge tube between the primary conductors of the first and second electric~l connector~
ancl for electrically coupling the secondary conductors of the first and secon~ electrical connectors. The mountin~ device has a ~nown inductance which interact~ with the capacitance of the discharge device and stray capacitances or the com~ination thereof in order to produce a desired characteristic impedance ~typically that of the radio 4requency cable~, whereby the suppressor will dissipate electrical sur~es while representing a low standing wave ratio for radio frequencY energy transmitted along the cable.

~RIEF DESGRIPTION OF THE ~R~WINGS
Other objects~ features and advantacJes of the present invention will be apparent from a study of the written description and the drawings in which:
FIGURE 1 illustrates a frontal perspective view of a first preferred embodiment of the connector for electromagnetic impulse suppression.
FIGURE 2 illustrates a side elevation of the first preferred embodiment illustrated in Figure 1 without the co~er being attached thereto.
FIGURE 3 illustrates an end p~rtially sectioned view ~howing one connector and the gas discharge tube in ~he orientation envi~ionecl by the fir~t preferred embodiment without the cover being attached thereto.
FlGU~E 4 is a top elevation view of the -first preferred embodiemnt of the present invention without the cover being 53~
attached thereto.
FIGLI~E 5 illustrates a second preferred emt.odiemnt of the present irvention which utilizes a metallic shield rather than the non-metallic shield utili~ed in the first preferred ~mbodiment.
FIGU~E ~ illustrates a partially cross-sectioned top ~iew of the second preferred embodiment ta~en alon~ the section lines 6-~ of Ficlure 5.
FIGURE 7 illustrates the schematic lumped circuit constant elements and diaclram for the theoretical reconstruction of the unshielded ancl unbalanced coaxial lir,e version of the present invention illustrated generally in Figure 1.
FIGU~E ~ illustrates the schematic lumped circuit cor,star,t elements and cliagrams for the theoretical reconstruction of the shielded and un~alanced coaxial line version of the present invention illustrated in Figures 5 and 6,appearingwith Figs. 1, 2, 3 and 4.
FIGU~E ~ illustrates the lumped circuit elements and schematic diagrams for the technical reconstruction of a ~alanced line unshielded and shielded version of the present invention.
FIGURE ~ illustrates a ~ottom perspective view of an alternate preferred embodiemnt of the present invention which i 5 specifically desicJned for use with ~alanced open line transmission cables.
In the drawings~ e reference numerals will refer to li~e parts throughout the several views of each of the em~odiments of the present invention. However, variations and modifications may be effected without departin~ from the spirit and scope of 30 the concept of the disclosure as defined by the appended claims.
It should ~e o~served that the elements and embodiments of the present invention have ~een illustrated in somewhat simplified form in each o~ the drawings and in the following specification in order to eliminate unnecessary and complicating details which would ~e apparent to one s~illed in this art. Therefore ! other specific forms ~nd constructions of the invention will be equivalent to the embodiment de~cri~ed although dep~rting somewhat from the exact appe~rance of the drawings.

TECHNIC~L THEORY DISCUSSION
By utilizing some common fundamentals of electronic low pass filter-matching, a standard T or "1r" networ~ configuration can ~e calculated so as to utilize the cap~citance of a gas tu~e or other discharge device as a partial or entire cap~citor leg of the filter circuit. The unit would ~e imped~nce transparent for only ~ narrow group of RF frequencies and thus the efficiency of the tu~e or discharge device as a protector would ~e degraded.
Bince a tr~nsmission line consists of series distributed inductors ~herein ~nown as L's) whose reactance value ht any frequency exactly equ~ls the reactance v~lue of a plurality of shunt distributed capacitors (herein ~nown as C's), the tr~nsmission line can be synthesized over a wide frequency range as consisting of lumped L's and C's.
If ~ "T" or "~r" circuit is mirror-ima~ed below ground, ~nd if the ground is then eliminated (such as in ~ balanced circuit~, the circuit will be identical to the circuit of ~
synthesized lumped transmission line. By a~ain utilizing the cap~citance of ~ gas tube or discharge device as a partial or whole capacitor leg in the lumped transmission line9 the discharge device will become an integral part of the ~djacent section of the transmission line. Since transmission lines in ~eneral can be used from very low frequencies to micr~wave frequencies, the efficiency of the tu~e as a surge protection device is not de~r~ded. Thus, it should now ~e app~rent that the synthesized lumped element transmission line is a special application of the cyeneral T or 1~ networ~ circuit designs.
Since only one C value is o~ interest (that o4 the tube or the tube paral1eled with another C>, the synthesized lumped 10 .

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transmission line will therefore be segmented as a mirrored T
configuration a~ opposed to the mirrored "~ "configuration.
This will elimin~te the need for an additional C and will allow the gas tube or discharge device capacitance to be bufferecl on each side by only L' 5 .
This sectior of a synthesized lumped transmission line can be made to present any characteristic impedance, as well as being either balanced or unbalanced, and may be constructed with either air or solid dielectric materials.
To calculate the required C value for anY tr~nsmission line, the following formula can be used:

~ x 1 ~
C= ----------------- = ~F~inch Where Z~ i 5 the desired ch~racteristic impedance (typically the same as the transmission line) and K is the dielectric conctant.
To calculate the required L v~lue for any transmission line, the following formula can ~e used for the same values of and K:

1.016 ZO ~ ~3 L= -------~ -- = ~H/inch 1~

In the unbalanced unshielded type configuration shown in Figure 7, the gas discharge tube may be mounted ~etween two connectors for convenience. The center connector pins compri~e L31 and L32, and the gas tuhe comprises C50 and i 5 ~oldered to mounting screw L40. The m~in mounting screw L40 is of ~maller diameter and longer in length than the center connector pins L31-32 and thus will have more inductance than required. Therefore, an additional screw of inductance L42 i~ added in parallel to reduce the total inductance value. This total value equals the calculated L value, as do L31 and L32 when added together. The formul~ for calcul~ting these straight 1ength induct~nces c~n be found in moct engineering textboo~s.
This ideal connector configuration typically shows no 11 .

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~erformance degredation bec~use of its extreme short length when used in conjunction with the typical unbalanced coaxi~l transmission line, ~ut only as lor,g ag conductive material ~which upsæts the inductive to capaciti~e ratio balance~ is not brought within close proximity of the connector. In order to pre~ent this reactance imbalance, the unit should be housed in a plastic shell ancl a standoff mount should be used ~which should also he used in the calculations of L~. This standoff also pro~icles a connection to ground so that the gas discharge tube can conduct the impulse to ground.
In ~n unbalanced, metal enclosed, coaxial line configuration illustrated in Figure 7~! the physical size of the tube causes the presence o4 additional strar C. This requires that the smallest dimension gas discharge tube should be used with low L standoffs. With a slight increase in the normal concentric size of the outer conclucti~e shell, the inner to outer conductor size relationship is chanc~ed from the particular line characteristic impedance. This will cause an increase in L
due to a decrease in distri~uted C. This is again restored to the desired impedance by inserting the g~s discharge tube as a 1umped capacitance ~alue.
The following formula is useful for calculating the required C ~alue for this coaxial line with relationship to the inside to outside diameters:

7~62K x 10 C= ---------------- = ~ F/inch 12 1O5lo ~/d where D is the outside diameter, d is the inside diameter and K
is the dielectric constant.
The following formula is useful for calcul~ting the required L ~alue for this coaxial line 3 as abo~e:

L= 11.684 log)O ~/cl x 10 = ~ H/inch or L=(140.208/12~ loglOD/d x 10 = ~ H/inch for the desired characteristic line impedance Z~ =

12.

~ ~53~
Balanced transmission lines, either shielded or unshielded, can be treated in the ~ame manner as pre~iously mentioned for unbalanced lines. Figure 8 illustrates a schematic diagram of ~a1anced, un~hielded transmission line. Since the ~F currer,ts throuqh capacitors CI50b are equal and 1~0 degrees out of phase, there exists a ~Irtual ground where they join, and thi 5 ~irtual ground may be grounded. If a three element gas tube is substituted for the cap~citor C150, and the distance and~or dielectric material is changed such that the inducti~e and capacitive ~alues balance to produce the Z impedance, then the center element of the ga~ tube can be ~rounded for impulse protection. The three element ~as tube can therefore be thought of as two capacitors C15~a and C15~b in series. The following formulae may be u~eful for c~lcul~ting values for the un~hielded balanced line:

3.~1 K x 10 C= ------------------------ = ~ F/inch 1~ log~ 2~d and 0.28042 log~O ~fd 12 = ~inch where the relationship ZO = ~ is maintained for the desired characteristic line impedance, and where K i5 the dielectric constant~ D is the center to center distance between conductors and d is the diameter of the conductors ~both must be in the same units for these formulae)~
~ st~nd and a plastic enclosure are required for the same reasons as mentioned for the unbalanced unshielded ~ersion. For convenience, two ~imple 2-lu~ terminal strips may be used bac~
to bac~ and the three element gas tube soldered in place between them.

The shielded balancQd transmission line may be conceptuali ed as a combination of the balanced line and the coaxial line~ Because of the distributed capacitance to ground for both lines, the formulae are slightly more complex. Here, R

3'1~
will be substituted for Z~/d in the above formulae for simplicity.

~.68l K
C = ----------- x 10 = ~F/inch l2 1Og~OR
and . 2g042 1 oq~
L = -------- ----- = ~H/inch where ~ = (2h/d~ h~D~ 1+~hf~ ~ and K is the dielectric constant and h is the height abo~e ground and where ~ and d are as above.
In these formulae D d and h~d, while maintaining the ratio of L to C in the formula Z~ = ~ for the desired line impedance.
For ease of construction, the balanced unit may be redesigned and used inside a conductive shell similar to the unbalanced coaxial shell. In any of the units, depending on the C v~l~ue of the tube and the desired ZO~ the L values may be of a large value and thus warrant the use of discrete values of inductance (such as a coi1 or coiling of one or more conductors) in order to have ease o4 onstruction. ~ny discrete coil used should be analy2ed carefully for the reactance values ~nd for the rise time of the undesir~ble impulse.
Since a gas tube is somewhat power limited due to its 1imited heat dissipation factor, theræ is a need for fail-safe considerations. The unshielded types~ both balanced and unbalanced, should be constructed such that the gas discharge tube is soldered in place generally in a somewhat horizontal position. This allows the tube, when heated by shunting impulse energy, to heat to the melting point of the solder ~efore it disconnects itse1f and falls harm1essly away from its operati~e condition against th~ conductors.
The enclosed coaxial line configurations can handle more power since the outside shell can act as a heat sin~. However, as with the open line configuration, the tu~e should also be 14.

S3~
oriented ~o ~ to disconnect itself at. the melting point of the ~older so that it will fall away.
In order to indicate that the tube has fallen in the fail-safe mode 5 the unbalanced shielded and unshielded type shells should be made translucent 50 that a visual or an optical sensor indication would re~eal the situation. The enclosed coaxial types should ha~e a small hole or an optical sensor which would not degrade performance. Both systems could utili~e a system of monitoring for any change in ~SWR as an additional failure indication.
In both instan~es, when the ga5 discharge tUbQ clisconnects, the surge protection will be discontinued. However, by cascading additionRl equal threshold surge protection unit~ in the transmission line, protection can bæ continued since the tube closest to the impul~e will typically become the first conductive path. As the temperature of the tube rises from impulse conduction, its conduction threshold will lower and thus in~ure that a path to ground will be available for the next impulse.
It must be noteci that as a tube fails and decouples from the connectors, the additional protection from subsequent impulses can be provideJ by the cascade technique. However, once the ~as discharge tube drops out of the circuit1 the circuit is no longer transparent to RF signals and the ~SWR and insertion losses will both increase su~stantially.
The RF power handling capabilities of the unit can be calculated since the voltage threshold versus response time of the gas tube i5 i~nown ancl the transmission line impedance is also i<nown. These calculations however, are only valid under matched canditions (VSWR = I to I~. If this condition is not satisfied, the placement of the unit with regard to the stanciing wave will determine the RF handling capabilities.
The following embodiments of the present invention are practical ~pplications of the preceeding theoretical 15.

considerations. However, it should be noted that while a gas discharge tube is used for purpo~es of illustration, other gasseous or solid state discharge devices can be substituted provided that proper construction adjustments ~re made a specified in the prior formul~e.

16.

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DET~ILE~ C)ESC~IPTION OF THE PREFE~RE~ EtvlBO~I~ENT
~ first preferred embodiment of the conr,ector for electromagnetic impulse suppressic~n is illustrated generally in Fic~ure 1. While Fi~uræ 1 illustrates the unbalanced or coaxial line version of the present invention, other embodiments for use with open line transmission systems will also be within the scope of the appended claims.
The connector for electromagnetic impulse suppre~sion includes a base 10 manufacturecl of a metallic and conductive material for being coupled throuclh apertures 12 to a ~rounded or other conductive surface. The base 10 inclu~es a plurality of generally upstanding vertical supports 14 which are mechanically and electrically coupled to the base 10. The distended end~ of these vertical supports 14 are coupled to the lower sections of a pair of electrical connectors illustrated generally as ~.
The length of the vertical supports 14 are determined 50 as to provi`de a separation of approximately 1.~0 inch between the center of the paired electrical connectors ~0 and the base 1~.
This separation is important in orcler to minimi~e anY stray capacitance between the various elements comprisinc~ the paired connectors and the other elements spaced therebetween. These vertical supports 14 also provide some distributed inductive reactance ~s previously discussed.
~ s will be seen more clearly in FicJures 2, 3 and 4, the p~ired electrical connectors 2~ include a first electric~l connector 21 and a second electrical connector 22 which~ at least for 50 ohm coax, are typically Type-N coaxial connectors manufactured by ~mphenol under Part No. 82-24. ~onnæctors of thi 5 type have been chosen for low insertion loss at frequencies up to and exceeding 1,000 MHz. The generally upst~ndin~

vertical support~ 14 ~re coupled to the lower group of two apertures 24 in the paired electric~l connectors 20 by a plur~lity of bolt, nut and washer combinations ~6.

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The center cor,ductors 31 and 32 respectively of the ~irst electrical connector 21 and the second electrical connector ~2, are disposed adjacent to each other ~nd are electrically coupled through the use of a small center concluctor shown generally as 36. The size of this center connectin~ conductor 36 will generally be determined by the inside diameter of the cylindrical bores 10cated within the center conductors 31 and 32 of the connectors 21 and 22. This center connectin~ conductor 36 will typically be soldered to both the center conductors 31 and 32 in order to secure the separation therebetween. This separation is typically ~for 50 ohms~ on the order of 0.72 inches when measured from the inside surface 21a of the ~irst electrical connector 21 to the inside surface 22a of the second electrical connector 22.
This distance is somewhat critical in that the length of the additional inducti~e separators communicating between the base surfaces 21a and 22a will be determined by the distance between the center conductors 31 and 32. Since the length of these additional inducti~e separators is critical to the o~erall lump circuit element impedance of the connector and surge protector, these dimensions should ~e maintained or coordinated with the lumped circuit capacitance elements in accordance with the a~ove-explained formulae.
While the center conductors 31 and 32, together with the center connecting conductor 36 form the first or primary inductor (see L31 and L32 in Figure 7~, a second circuit inductor ~L40 in Fi~ure 7) is provided for coupling the second electrica1 conductors or shields o~ the paired electrical conductors 20. This second inductor has the form of a standard I
1/8" 4-40 machine head screw~ shown generally as 40, which communicates through the apertures in the flan~e mounting plates 21a and 22a of the respecti~e connectors 21 and 22.
The diameter and lenc~th of this screw 40 are somewhat critical since at UHF frequencies at or ne~r ~,000 MH~, the 1~ .

:1 ~h5314 diameter and the length of the screw would substantially determine the inductance of the element. Since the cro~s-sectional diameter of the screw 40 is slightly smRller than the cross-sectional diameter of the center conductors 31 and 32, the inductance of the second inductor 4~ is 1 ightly larger than the inductance of the center conductors 31 and 32.
Therefore, a second screw or supplemental second inductor 42 is secured through the aperture~ in the mounting flanges 21a and 22a of the connectors 21 and 2~ -for providing additional rigidity in the separation of these two connectors. Since the second screw 42 or supplemental inductor L42 is in parallel with the first ~crew 40, the total inductance of the two screws will be approximately one half of the inductance of a single one of the screwsO This combination results in the inducti~e reactance of L40 equaling that of L31 and L3~. It i6 this balancin~
together with the chosen C ~alue, that will substantially increase the frequency range at which the o~erall 1ump circuit elements will match the impedance of the tran~mision line coupled to the connectors ~1 and 22.

~ is more clearly illustrated in Figure 3, a fir~t end of a gas dich~rge tube 50 ~or surge arrestor tu~e) is electrically and mechanical 1Y coupled to the cænter conductors 31 and 32 of the paired electrical connectors 21 and ~2. This electrical and mechanical coupling is typically produced by soldering the middle section of the gas dischar~e tube 50 to the lower cylindrical surface of the center conductors 31 and 32 at a point generally adjacent to the center connecting conductor 36.
~ second section of the ga discharge tube 50 i mechanically and electrically coupled to the first screw ~second inductor) 40. Li~ewise, this coupling i tYpicallY ~ccomplihed by solderincJ an upper surface of the gas disch~rge tu~e 50 to a lower surface of the screw 40. The fact that the ga5 dischar~e tube 50 is coupled by oldering to the underneath surfRces of the center conductors ~1 and 32 and the screw 40 is significant 19 .

53~
in that it is a characteristi of such gag discharge tubes that they will be re~uired to dissipate as heat a part of the impulse energy which is conducted to ground through the de~ice, thereby increasing in ambient temperature. In order to provide a fail-safe mode so that the gas discharge tube 50 will not fail in a continuously conducting mode, and thus short out the transmission line, the heat buildup within the gas discharge tube 50 will typically melt the solder connections thus allowinc~
gravitational forces to disengacJe the gas discharge tube 50 from its connections with the first screw 40 and the center conductors 31 and 3~. Thi 5 disengagement will cause the gas discharge tube S0 to fall away from the onductors ~nd thus pre~ent damage to the tube 50 or to the other circuit elements.
Of course 9 when this gas disch~rge tube 50 decouples from the circuit elements, the main capacitance elements in the lump circuit analogy will have been remo~ed, thus causing an aberration in the insertion loss and the ~SWR along the transmission lines. While this increase in ~SWR is not helpful for the transmitter attached to the transmission line~ it is preferable to ha~e this 4ailure mode rather than to ha~e a failed gas discharge tube continuc,usly conducting and shorting out the transmission line.
Se~eral of these impulse protector connectors may be arranged in a series or a cascade fashion in the transmission line. In this manner if the gas discharge tube 50 in one of the units becomes o~erheated and disengages from electrical communicatic,n between its circuit elementsl the remaining units will nevertheles~ remain operati~e in order to absorb any electrical surges between the conductors.
In order to obser~e the normal coupling between the gas discharge tube S0, the first screw 40 and the center conductors 31 and 32, the cover 18 is typically manu~actrured of ~ c1ear or partially transparent plexiglass or plastic material~ This will allow ~isual inspection of the proper coupling of the gas 20.

dischar~e tube 50.
In the first preferred embodiment o4 the present inventior, it is en~isioned that the gas discharc~e tube 50 will be of the type produced by Tll INDUST~IES IN~. of ~00 North Stron~ ~venue, Lindenhurst, New Yor~ 11757, and designated as Model No.11.
This particular gas dischar~e tube is a 3-element ~of which only two elements are typically connected) design and has a firing or brea~down voltage of approximately 3~0 ~olts ~.C. ~5 soon a~ the voltage across the first and second sections of the ~o CJ~s di~charge tube 50 exceeds this brea~down volta~e, the rare gases within the tube will ionize and form a relatively low resistance path ~or shunt) between the two sections of the tube, and therefore between the center conductors 31 and 32 and the first screw 40. Since these elements are coupled to the center conductor and braid elements of the coaxial transmission line, the electrical sur~e occurring on either of these circuit cond~ctors will be essentially shorted to clround through the vertical supports 14 and the base 10.
This ~ag discharge tube 50 is substantially more tolerant to large electrical volt~ge pea~s than semiconductor de~ices~
but the terms discharge means or discharge device are intended to include both gas dischar~e tubes and functionally equivalent semiconductor devices ~such as diodes) in applications such as those not concurrently requiring a high brea~down voltage and low capacitance. Gas discharge tubes 50 of this tYpe are capable of handling without distruction sever~l impulses of the type which commonly occur in a 5 ingle lightning stri~e. The use of rarified gases within the discharge tubes subst~ntiallY reduces the vaporiz~tion and oxidization of the elements within the tubes following the ionization of the gas therewithin.
Furthermore, since the tubes 50 maY be manufactured with precise gaps and with ~nown gasses therein, the precise brea~down voltage of the tubes may be carefully and predictably determined. This factor is important for choosin~ the proper 5~

power hanclling capabilities or brea~down voltages of the gas tu~es 50 in accordance with the power handling requirements of the radio frequency transmission line ? wnile placing an accurate limit upon the highest voltage to be allowed along the transmission line as a result of power surges or lightining stri~es.
~ s was previously discussed, since solid state devices in transmitters and receivers coupled to the transmis,ion line are very unforc~ivin~ of these lar~e power surges or lightning stri~es, the accurate control of the maximum impulse voltage across the lines is most importarlt and the need for predictability is ubvious. While the TII Model 11 ~as discharge tu~e has been illustrated in the preferred embodiment of the present invention, other models, namely the TII Model 37 and ~oclel 4~ ~as discharge tubes5 may al50 be used. Ta~ing the T11 Model 11 3-electrode gas tube as an example~ the maximum D.~.
arc voltage under brea~down conditions (glow condition~ is approximately 30 volts. The ~as discharge tube is ~dvertised as ~eing expected to survive 29~0 surcJes of 10/1~ waveform~ at approximately 1,000 peal~ amperes each.
For a typical length of 50 ohm coaxial cable such ~s R~-3U
or RG-58U~ and for the typical ~odel 11 c~as discharge tube capacitance value of approximately 1.7 picofarads3 and for a K
value of 1 (corresponding to the device ~eing suspended in air~ ?
the value of the lumped circuit conductor inductallce L required for the entire connector assem~ly to represent a 50 ohm impedance would be approximately 4.~3 nanohenries per inch. ~y using the proper spacing between elements ~1 ancl 22, the length of elements 31 and 32 will each yield the 4.~ nanohenries per 30 inch necessary for elements L31 and L32. Using two 1 1~3" x 4-40 screws 40 and 4~ as the inductors L40 and L4~, the value of the resulting inductance is approximately 4.~3 n~nohenries per inch.
Therefore, as constructed and illustrated ir, Figure ~ ~ and 4, the electromagnetic impulse suppressor will have a 22 .

~ ~ ~53~
characteri~tic impedance of approximate1y 5~ ohms for electrical ener~y from ~LF to UHF frequencies.
Experimental data of the preferred embodiment of the present inventior, indicates that tube insertion losse~
~exclusive of connector losses~ on the order of 0.1db at 4~0 MHz and 0.18 db at 1,000 MHz are obtainable in test unit~. These insertion losses typically will decrease to below 0.01 db at frequencies below 200 MHz. VSWR values on the order of i.1:1 at 1,0~0 MHz ~nd 1.~1:1 at 2~ MHz are o~tainable from production units. It will be obvious to one s~illed in thi~ art that these figures for insertion io5~ and ~SWR are substantially below other available commercial units. ~5 previously explained, most other commercial units are unable to ~e operated with reasonable insertion losses and ~W~ figwres above 300 MHz. In contrast, the present unit~ are well-swited for operation up to and exceeding 1,000 MHz.
~ second preferred embodiment of the present invention corresponding to an unbalanced shielded version is illustratecl ~enerally in Fic~ures ~ and ~. The second embodiment differs from the first embodiment illustrated in Fi~ure~ 1 through 4 in that no base 1~, vertical supports 14 or non-metallic cover l3 are provided. Instead~ the seconcd preferred embodiemnt is provided with a metallic cover 118. The fir~t and second electrical connectors 21 and 22 are coupled to the planar surfaces of the metallic cover 118 in a manner similar to the couplin~ with the plates 21a and 22a of the first preferred embodiment. The center conductors 31 and 3~ of the electrical connectors ~1 and 2~ are al 50 electrically and mechanically coupled ~0.3 inches in diameter) as in ~he first preferred em~odiment. However, in view of the larcJe surface area and the low inductance of the metallic cover 11~, separate screws for additional inductors 4~ and 4~
are not required as in the first preferred embodiment. Instead, the entire surface of the metallic cover 118 acts as a conductor which unbalances the circuit and shields the other circuit mem~ers. For a typical 50 ohm unit, the size of the metallic cover 1l8 is approximately 1.50 inches in owtside diameter, 1 inch in length and 1~32 inches in thic~ness. These præferred ~izes and dimensions produce an inductance which is approximately the same as the inductances 4~ and 42 in the first preferred embodiment.
In the second preferred embodiment ~s illustrated in Figure 6, the gas discharge tube 50 has a first section 51 thereof coupled directly to the center conductors 31 and 32 and a second section 52 ~throu~h a standoff 52~ thereof coupled to the insicle circumferential surface of the metallic cover 118. ~s in the case of the first preferred embodiment7 the gas discharge tube 50 is soldered to both the center conductors 81 and 3~ ~nd to the metallic cover 118. In this manner when the heat dissipated by the conductin~ gas discharge tube 5~ raises the temperature beyond the melting point of the solder used in the connections!
the 501 der will melt and the gas discharc~e tu~e will be drawn by ~ravitational forces away from the center conductors 81 and 82.
~ mount similar to the first preferred embodiment may ~e used for proper orientation and grounding of the tube 50. It should be pointed out that ~ structure of thi~ type m~y not be required since the coax and its connectors could generally support and orient the tube. The grounding will depend on the system installation and type of coax. However, for ease of installation a stand similar to the supports 124 of the first preferred e~bodiment would appear to be best suited.
With reference to Figure ~9 a balanced line version of the present invention is illustrated as being interposed along a length of typical 150 ohm twin-lead transmission line 60. ~
first conductor ~1 and a ~econd conductor ~2 of the twin-lead transmission line 60 are routed through insulators 17~ contained in two parallel plates 128 which represent the shortened plan~r surfaces of a non-metallic cover 1~8 similar to the non-metallic cover 18 of the 4irst preferred embodiment. Each o-f these

2~.

5~

circuit condu~tors 61 and ~2 ~re extendæd into electricRl communication with the corresponding conductor on the adjacent piece of transmission line buy a onductor 1~1 and 162 respectively. The length and diameter of the conductors 161 and 1~2 ~re typically chosen in ~ccordance with the inductance and impedance formulae which have been previously discussed. These inductors, depending on the formulae~ maY consist of actual coils for some impedances.
~ gas discharge tube 150 includes ~ first end 151 which is coupled to one of the circuit conductors 161 and a second end thereof 15~ coupled to the other circuit conductor 162. The center portion of the gas discharge tube 153 i5 coupled throuclh a relatively larc~e grounding str~p 16~ to cJround potential. This ground potential m~y be provided through generally low induct~nce upstanding supports and a base simil~r to the same elements 14 and 10 in the first præferred embodiment il1ustr~ted in Figure 1.
The electrical schematic diagr~m of the equivalent lumped circuit elements for the balanced line conficJuration of the present invention is illustrated generally in Figure ~. The two upper inductors L161 correspond to the circuit conductor 161 which couples together the first circuit conductors within the twin-lead transmission line 60, while the lower inductors L162 comprise the circuit conductor 162 which couples tocyether the second conductors within the twin-lead tr~nsmission line 60. The capacitor C150 comprises the two capacitive elements within the

3-element gas discharge tube 150. The values and interaction between e~ch of these lumped circuit element4 has been previously discussed in accordance with the formulae mentioned above.
For a typical 150 ohm impedance balanced line, the values of L161 and L162 would be approximately 12.7 nanohenries per inch. Thus, L161 and L162 could be manufactured of ~.125 inch diameter wire having a length of approximately 1.25 inches. The 25.

Tll ~as tu~e Model 11 ~element 150~ is ~oldered ir,to place as illustrated in Figure ~0 This gas tube 150 ha~ an end-to-end capacitance of approxim~tely 0.7 picofarads. The end planar elements 128 would be spaced apart by approximately 1 inch so as to provide sufficient separation for the inclusion of the gas tube 150.
With continuing reference to Figure ~, a balanced line shielded version of this alternate embodiment would be simil~r to the unshielded version with the exception that a met~llic shell, ~imilar to the one illustrated as 118 in Figure 5, would surround the b~sic ~al~nced configuration. The si2e of thi 5 metallic shel1 and the new L value~ would be calculated in accordance with the formulae described pre~iously. The electrical schemati diagram for the balanced shielded embodirnent would also be the ~ame a5 the balanced ver~ion shown in Figure 8.
Typically, the balanced ~nd shielJed embodiment would be inter~ch~ngeable with the balanced unshielded embodie~nnt, and the unb~lanced and unshielded embodiment would be interchangeable with the unbalanced shielded embodiment. One major advantage of the ~hielded embodiment is that any conductive objects which are in close proximity to the connector~ ~1 and 2~ will not cause a significant unbalancing of the impedance through the device primarily due to stray capacitance.
This isolation from nearby conductive objects, as was previously dis ussed, i 5 the primary reason for utili~ing the base 1~ and the vertical supports 14 of the preferred embodiment. ~lso, as was previsusly discussed, the vertical supports 14 and the base 10 pro~ide a second~ry grounding function for providing a more direct circuit conduction of the impulse voltage to ground, rather than depending upon the conduction of the impulse down the grounded or shielded portion of the cable. The lower material costs and the ~uperior 26.

~ ~5~3~'~

~roundin~ features of the first embodiment as illustrated in Figure 1 ma~e it the preferred embodiment for normal coaxial cable applications.
The preferred embodiments of the present invention may now be distinguishecl from the prior art reference~ which have already been discussed. First, none of the prior art neferences utilize a matching networ~ or other impedance sensitive desi~ns which attempt to match the impedance of the mounting devices, or other circuit elements which support or are connected to the gas di~charge tu~e, in order to minimize ~SWR and insertion losses.
This should be contrasted with the present invention in which the primary structural ccnsiderations for mountinc~ the gas dischar~e tube directly relatæ to the ~alues of thæ equivalent lump circuit elements for inductance and capacitance which are required in order to maintain the same effective characteristic impedance for the connector ~s for the transmission line with which~it is used.
SecondlY? none of the prior art references discuss applications for impulse suppressor connectors which extend in frequencies up to and beyohd 1,0~g ~Hz. Most of the prior art impulse protection connectors are limited by the inductance and capacitance of their constituent element~ to operate at frequency ran~es below 300 MHz ~with accepta~le ~SWR and insertior, loss figures~. Thirdly, the present invention is designed for use with high-powæred VLF to UHF transmission systems and are not limited in use with ~JHF or UHF receivin~
systems a5 Wi th prior art desicJns.
The embodiments of the pre~ent electroma~netic impulse suppression connectors have been described as examples of the invention A~ claimed. However, the present invention should not be limited in its application to the detail 5 and constructions illustrated in the accompanyin~ drawin~s and the specification~
since this invention may be practiced or constructed in a variety of other different embodiments. ~lso~ it must be 5~
understood that the terminolo~y ~nd description~ employed herein ~re used solely for the purpose of describin~ the ~ener~l concepts of the in~ention ~nd the pre4erred embodiment best exempli4yinc~ these concepts~ ~nd there~ore should not ~e construed ~s limit~tions on the in~ention or its operability.

28.

Claims (23)

WHAT IS CLAIMED IS:

1. An electrical surge suppressor for dissipating electromagnet-ic impulse energy along a radio frequency signal transmission line of the type having primary and secondary conductors and a known characteristic impedance therebetween, the suppressor comprising in combination:
paired first and second electrical connectors each having primary and secondary conductors for being operatively interposed along the primary and secondary conductors of the radio freq-uency signal transmission line;
discharge means for defining a known breakdown voltage and a known capacitance between first and second sections thereof;
and mounting means for electrically coupling said first section of said discharge means between said primary conductors of said first and second electrical connectors and for electrically coupling said second section of said discharge means between said secondary conductors of said first and second electrical connectors, with said mounting means having a known inductance which interacts with said capacitance of said discharge means and any stray capacitance of the combination thereof to produce a characteristic impedance which is generally equal to the characteristic impedance of the radio frequency signal transmission line whereby the suppressor will shunt electrical surges while normally representing a low standing wave ratio for radio frequency energy transmitted along the transmission line.

2. The surge suppressor as described in Claim 1 wherein said mounting means comprises in combination:
first inductor means operatively coupled between said primary conductors of said first and second electrical connectors for supporting said first section of said discharge means;
and second inductor means operatively coupled between said secondary conductors of said first and second electrical connectors for supporting said second section of said discharge means, whereby said discharge means is electrically coupled and supported between said first and second inductor means.

3. The surge suppressor as described in Claim 2 wherein said first inductor means comprises a first support element attached between adjacent sections of said first and second electrical connectors for maintaining a known separation therebetween.

4. The surge suppressor as described in Claim 2 wherein said second inductor means comprises a second support element attached between adjacent sections of said first and second electrical connectors for maintaining a known separation therebetween, with said second section of said discharge means being attached to said second support element intermediate said first and second electrical conductors.

5. The surge suppressor as described in Claim 4 wherein said second support element is electrically coupled in parallel with said first support element so as to reduce the effective inductance of the combination thereof.

6. The surge suppressor as described in Claim 2 further including safety means for electrically disengaging said discharge means from at least one of said first and second inductor means responsive to the temperature of said discharge means exceeding a predetermined limit, whereby abnormal impulse energy dissipated as heat by said discharge means will decouple said discharge means.

7. The surge suppressor as described in Claim 6 wherein said safety means comprises solder for coupling said discharge means 30.

to said first and second inductors such that said discharge means will be detached by gravitational forces when said solder liquifies.

8. The surge suppressor as described in Claim 1, wherein said discharge means comprises a gas-filled discharge tube for at least partially dissipating the energy of the electrical surge therein.

9. The surge suppressor as described in Claim 2, wherein said mounting means electrically positions said discharge means symmetrically between said first and second electrical connectors.

10. The surge suppressor as described in Claim 1, wherein said discharge means comprises a non-air gap type device.

11. The surge suppressor as described in Claim 2, wherein the transmission line comprises a coaxial cable having a center conductor and a shield and wherein said first inductor is coupled to the center conductor of the coaxial transmission line and wherein said second inductor comprises a conductive surface coupled to the shield of the coaxial transmission line for defining a cavity which contains said first inductor and at least part of said discharge means therein.

12. The surge suppressor as described in Claim 11, wherein said discharge means comprises a discharge tube filled with a gas.

31.

13. An electrical surge suppressor for shunting electromagnetic impulse energy from the center conductor to the shield of a coaxial transmission line having a known characteristic impedance, the electircal surge suppressor comprising in combination:
a first conductor interposed between adjacent sections of the center conductor;
a circumferential conductor interposed between adjacent sections of the shield so as to define a cavity for shielding said first conductor therein;
discharge means for defining a known breakdown voltage and a known capacitance between first and second sections thereof, with said first section coupled to said first conductor and with said second section coupled to said circumferential conductor such that said discharge means is at least partially contained within said cavity defined by said circumferential conductor;
and wherein the inductance of said first conductor and said circumferential conductor interact with said capacitance of said discharge means and stray capacitance of the combination thereof so as to produce a desired characteristic impedance generally equal to the characteristic impedance of the coaxial transmission line, whereby the surge suppressor will shunt impulse energy exceeding the breakdown voltage of said discharge means from the center conductor to the shield while normally representing a low VSWR for radio frequency energy transmitted along the coaxial transmission line.

14. The surge suppressor as described in Claim 13 wherein said discharge means comprises a non-air gap type device.

15. The surge suppressor as described in Claim 13 wherein said discharge means comprises a discharge tube having a gas other than air therein.

32.

16. The electrical surge suppressor as defined in Claim 13 wherein said first conductor comprises the center conductor sections of oppossing coaxial connectors.

33 .

17. A combination matching network and electrical surge suppressor for matching the charactreristic impedance along a coaxial cable and for shunting electromagnetic impulse energy from the center conductor to the shield thereof, the device comprising in combination:
paired first and second electical connectors each having a primary conductor coupled to the center conductor of the coaxial cable;
a circumferential conductor interposed between adjacent sections of the shield of the coaxial cable so as to define therein a cavity for containing said primary conductors of said first and second electrical connectors;
discharge means for defining a known breakdown voltage and a known capacitance between first and second sections thereof with said first section coupled to said primary conductor and with said second section being coupled to said circumferential conductor such that said discharge mean is contained at least partially within said cavity; and wherein the inductances of said primary conductors and said circumferential conductor interacting with said capacitance of said discharge means and stray capacitances of the combination thereof so as to produce a desired characteristic impedance having a known relatitonship to the characteristic impedance of the coaxial cable, whereby the device will normally represent a low VSWR for radio frequency energy propagating along the coaxial cable.

18. The device as described in Claim 17 wherein said discharge means comprises a non-air gap type device.

19. The device as described in Claim 17 wherein said discharge means comprises a gas discharge tube having therein a gas, other than air.

34.

20. The device as described in Claim 19 wherein said discharge means is positioned generally symmetrically between said first and second electrical connectors.

35.

21. A method for matching the characteristic impedance of a radio frequency transmission line of the type having first and second conductors while shunting electromagnetic impulse energy traveling therethrough, said method comprising the steps of:
(a) electrically interposing primary and secondary conductors along corresponding first and second conductors of the transmission line;
(b) coupling discharge means, for defining a known breakdown voltage and a known capacitance, between said primary and secondary conductors; and (c) matching the characteristic impedance of the transmission line with the characteristic impedance represented by the combination of said primary conductor, said secondary conductor, said discharge means and any stray capacitance associated with the combination thereof, while enabling said discharge means to shunt electromagnetic impulse energy between the first and second conductors of the transmission line.

22. The method as described in Claim 21 wherein step (a) comprises the substep (a1) of interposing first and second electrical connectors each including said primary and secondary conductors along corresponding first and second conductors of the transmission line, with said primary conductor being defined as the center conductor of said connectors, And with said secondary conductor being defined as a circumferential member for surrounding and shielding said primary conductor and at least part of said discharge means therewithin; and wherein step (c) comprises the substep (c1) of using the inductance of said center conductors of said first and second electrical connectors as the predominant inductance for interacting with said capacitance of said discharge means for matching the characteristic impedance of the combination thereof with the characteristic impedance of the transmission line.

36.

23. The method as desscribed in Claim 22 wherein said discharge means comprises a gas discharge tube of the non-air gap type and wherein step (c) includes the substep (c2) of minimizing the capacitance of said gas discharge tube and any stray capacitance associated therewith.

37 .