CA2219125A1

CA2219125A1 - Coaxial cable tap

Info

Publication number: CA2219125A1
Application number: CA002219125A
Authority: CA
Inventors: Gerald L. Shimirak; Philip Vail; Alexandru S. Gliga; Nelson M. Shen
Original assignee: Individual
Current assignee: Raychem Corp
Priority date: 1995-04-24
Filing date: 1996-04-23
Publication date: 1996-10-31
Also published as: EP0823136A1; TW307935B; AU5569996A; BR9608263A; WO1996034428A1; AR001694A1

Abstract

A method of forming a tap into an intermediate point on a continuous coaxial cable comprising an inner conductor, a dielectric surrounding the inner conductor, and an outer conductor surrounding the dielectric. The method comprising the steps of: forming an opening in the outer conductor of the coaxial cable (1000); forming a cavity in the dielectric under the opening;
and mounting a tap insert (20) to the coaxial cable, the tap insert comprising a signal chip (22), so that the signal chip (22) is located in the cavity adjacent to the inner conductor of the coaxial cable, and can extract or insert or both a signal from the inner conductor. The tap assembly comprising a tap housing (100) and a tap insert (20). The coaxial cable tap housing (100) comprising; a first end portion; a second end portion; an intermediate portion having a recess (14); means for fixing the housing around an intermediate point on a continuous coaxial cable; an alignment element (12) having a known spatial relationship with the recess (14); and means for mounting a tap insert to the recess (14). The tap insert (20), comprising: a tap faceplate (21) comprising: an inner face, an outer face, means for mounting the tap faceplate (21) to a cable tap housing (100), and means for environmentally and electromagnetically sealing the tap faceplate (21) to the cable tap housing (100); a signal chip (22) mounted on the inner face of the tap faceplate; and means for providing RF input and/or output, said means mounted on the outer face of the tap faceplate (21).

Description

W 096/34428 PCTnUS96/05674 '. I' -1-CO~AT,C~T~T,F,T~P

This invention relates to coaxial cable taps.

Co~xi~l cable is widely used in the c~ ir-~tion industry to distribute television (TV) and other signals. This cable typically comrri~eS: a center con~urtol along which the signals are 1....~ l a Ai~lectric ~u~ lding the center con~ ctor; a, rigid outer cont1nr,tor cylinder which shields the signals from leakage and i~l..r~.c~ce;
and, optionally, a ~lo~e~ , incnl~ti~, outer jacket.

As used herein, a "tap" is a means by which a signal can be e ~ led from and/or ~s~ltd into a coaxial ~li~iblution cable so that signals can be passed b~lwt;~n the ~li~ibllti~n cable and a S~lbsr~ihPr's ple~ises. As used herein, a "tap assembly" is a device which is co~ to a coaxial cable to form a tap in the cable.
The known ~,ocedu,c for i ls~.ling a tap into a coaxial cable is time CO~ ..;..gand labor hllt~ive, and, when a tap is being added t~ an o~ - ~ Fr cable TV system, hlltllu~lS service. Thus, the coaxial cable is severed, both free ends of the severed coaxial cable are p ~p~ed with a coring tool, a co~ lo~ is in~t~llP~l on each of the two 20 pl~,~,~cd ends, and a tap assembly is h s~.ttd bcl~._.,n the two C'?~ . In order to Qrco~ o~Qte e-~vi"~"~F~ S~tS, a length of the coaxial cable ~ u~ding the tapmust be formed into an ~ ;on loop. The tap &~ bly typically provides coln~P~ oncfor s~lbsrriber drops, such as RG59 and/or RG6 drop cables.

It is CO.. ~OI- pr~tice to ~t~ u~t cable television service dow~ll~,~n of the poin.t where a tap is being added to an o~,-.,l;.-g distribution cable. IL,~ r, so that cab1~
co...l.~..ies may expand to provide, for eYQmrl~, telephonP- or other services le~lu~ g ~ ;"l~ .u~ted op~QtiQn~ it is ~-~ce~ that taps be cQrQhle of being made without illh.~u~tillg the signal pas~ g on the cable.
We have disco~ d a m~,th.)~l Of in~QllinjE~ a tap into a coaxial cable without having to sever the coaxial cable, and a coaxial cable tap assembly suitable for use in the in!ctQllQtioI~ method. The invention permits the in~Qll~tion of a tap into an op~ g W~ 96134428 P~llu~ 7 .. ..
coaxial distribution cable without illt~,.,u~i,lg the signal ca~ied on the cable. The methodl and tap assembly of the invention may be used for inct~ tion of taps in new cable inct~ tiQn~ as well as for adding taps to ol)ela~ Sy~t~ S.

In a first aspect, the invention provides a method of forrning a tap into an ..".~ e point on a CQ~ vu~ coaxial cable co...~ an inner cnn~ ctor~ a ~liçlectric surrounding the irmer c~ or, and an outer c~nflllctor ~u,luu.ld~g the ectnC, the m~tho~l co...l.~ the steps of:
a. forming an o~g in the outer con~ ctor of the coaxial cable;
0 b. forming a cavity in the ~1ielçctric under the V~lill~,; and c. mounting a tap insert to the coaxial cable, the tap insert col~ a signal chip, so that the signal chip is located in the cavity ~ c~ -~ to the inner co~lu~ilvr of the coaxial cable, and can (i) extract signals from the inner co~llv~-lor, or (ii) insert signals into the inner con~ ctQr, or (iii) do both (i) and (ii).

In a second aspect, the invention provides a coaxial cable tap h....~;;..p, snit~ble for uce in the m~th- ~l of the first aspect of the invention, the tap hollcing col . .~ g.
a a first end portion, b. a second end portion;
c. an ;l -- ~ii l~ portion _aving a recess;
d. mear~c for fixing the ~v~n~g around an ;.,t~ eA;~ point on a co..~;...~v~
coaxial cable;
e. means for cle~ ;c~lly and c.lVilvl~ ly sealing the tap houcing to the coaxial cable;
f. an ~liP~ el~n.~--1 h-aving a known spatial r~l~tionchip with the recess;
and g. means for lllou~ g a tap insert to the recess of the tap huu~g.

In a t_ird a~cpect, the invention provides a tap insert, suitable for use in the method of the first aspect of the invention, the tap insert co. . .~ -g a a tap f~F~t~ C~
i. an inner face, W 096~4428 P ~ AUSg6/~S~7 3~
ii an outer face, iii. means for moul.ling the tap rac~lale to a cable tap housing, and iv. means for cllvi~ 11y and electrom~gnetically sealing the tap faceplate to the cable tap housing;
b. asigr~alchip.. ,~ 1Ontheinnerfaceofthetap r;1r~1~lt,and c. means for providing RF input andlor output, said means mounted on the outer face of the tap r~

In a fourth aspect, the i~ iun provides a kit of parts s~1itable for l~....;..g a tap into an i.. l~ e point on a C4.. 1;~ 0~ coaxial cable, the kit co.. ~ ;.. g a. a coaxial cable tap hou~i~g capable of ~tt~hin~ around an i.,l. -.,.PAi~t~
point in a continuous coaxial cable; arld b. a tap insert c~ r ~p. ;~ g a signal chip, the tap insert capable of l~ h;.~, to the tap l-- .IX;~, after an OpChillg has been rnade in the outer con~ r,tor~ anda cavity has been rnade in the dielectric, ofthe coaxial cable.

In the method of in~ ti-n, an u~ is cut in the outer con~lnctor of the coaxial cable and a cavity is cut in the ~l;rl~-;c beneath the o~ -g in the outer con~luctor. In ~,~,f~ ,d f~.m~;.. lx, the O~ing and the cavity are elon~te and20 lon it~ in~l; huwc;vw, other shapes may be used. Typically the o~.""g and the cavity in the f~ ctric ~"ea~ it are cut at the same time using a cutting tool, e.g. a rotary cutting tool, ,u~rc~hle a rotary saw blade sized to cu,,~ .ond to the desired ~l;..-f--.~;ûns.
I~,f~,~ably a guide is used to position the tool and to help to control the ~l;...f -.~;..l.~ of the opening and the cavity. F~,f~.ably the tap h~ p is first ;~ h~l to the cable and is thal 25 used as a jig to guide the cutting tool. The tap ho. .~ p may have a ,~ cç~-~ed area ~ U13I1 which the blade of the cutting tool is m3_.ted, and an ~li nm~nt clc-.-~ having a known spatial re1~tion~hir with the recess. The ~lignm~nt Clc-.,~ serves to position the cutting tool with respect to the recess, and to define the ~ ;c)n~ of the cut by limiffng the range of motion of the cutting tool. If desired, the cavity in the ~lielPct~ic may be enlarged 30 after the cutting tool _as been used, ~er~,.dbly using a non~ e1;ve tool so that signal!j carried by the inner con~uct r are not disbJrbed. After the Gp.,.f~l~g and the cavity have been cut, a tap insert may be ~ 'hP~ to the tap hou j,ng, the tap insert compri~ing a signal wo 9bl34428 P~rluss6J~5674 , .
chip which enters the cavity in the (1iPIectric of the coaxial cable through the recess in the tap housing and the openil,~ in the outer con~ ctor of the cable.

The signal chip, mounted to an inner face of the base~ldle of the tap insert, i., electric~lly co~ ecl to means for oul~ul~ulg and il~UUill~, RF signals. Typically Co~ f'Ct~:; such as F-ty~e co~ , re mounted on an outer face of the bas~lale of the tap insert, and would CO~ f~Ct to drop cables to s~lbs~-~iher ~,~ises.

In p,ef~ ,d embo-l;...f...~, the tap ho,~ is co...~ fA of a metal such as 0 al-----;.----.. However, other suitable m~tP i~le such as a plastic with a co~lu~iliv,., coating on its inner surface could be used.

In ~r~ d embo~ the tap housing is used as a jig for the cutting tool a~;
desrrihe~l above. However, it is also posc ihle to cut the o~.fing and/or the cavity~, in the 5 same or s~ le opf~ti~me~ before the tap hvu~g is applied to the cable, or to do so after the tap housing has been applied but without using the tap housing to guide the cutting tool. Any jig sl~it~ble for poeitioning the cuffing tool and controlling the ~l;...~..e;on.e of the opening and/or the cavity may be used. For ~Y~mplç, a s~le jig carl be used to cut the o~g and cavity in the cable, and then the tap h~r~il~g in~ d on 20 the cable, with the recess in the tap housing aligned over the o~l~ing and cavit~
previously cut in the cable.

It is ~çeir~ble to use a tap h.,..~;.." with a recess and a means to attach a tap insert to the tap h~ ';;.-g This fi~-'.ili~tPS removal of the tap insert for adj~ -l ",~;,.t~ ."--~I'e 25 and the like. However, in some r.mho.~ ; it is also poesihle to use a tap huu~ g to which the signal chip is ~ , and which does not, ~ ~r~l~" need a recess ~ou~h which the signal chip is ~,.t~,d. Such a tap housing is applied to the cable after the opening and cavity have been cut in the cable.

It is plef~ d that the tap ~es~nbly provide an el~;hc,.. ~gntotic seal around the opening cut in the outer co.~ ,ctc~l in order to shield against signal leakage out of, and i lL~,.L..,nce into, the o~g. An inner surface of the tap housing makes electriç~l contact with the outer surface of the con(1llctor of the cable in an area su~lvu~ g the wo 96134428 PCI/US96105674 . . -5 -opening in the outer ct~n~ ctor. The two halves of the c~ xl~ 1-style tap housing are sealed with an EMI gasket (not ill--e~te~l in any of the figures), and the ;..~ r~ce ~ ,ell - the tap insert and the tap housing is also sealed with an EMI gasket (not i11~ te(1 in any of the figures).

The ~,ef~le~ cutting tool is a rotary saw. However, other suitable tools, e.g. arouter, may be used in conjullclion with a suitable cwl~ uli~p jig and/or ~ nmr~11t cl~ .1 on the tap housing. The edge of the recess may provide the ~li~m~ont means, e.g. for a router fitted with a bit having a top bearing.

It is de~ b1e to provide a flat signal strength over the ~ e~l frequency ulll along the length of the coaxial cable. A t~rli*r n~l tap assembly has a flat coupling ~ffi~ nr y over the ~ u~c.~ range. The slope of the signal ~L..,n~lll of a tapped off signal col~ onds to the slope of the signal ~ in the coaxial cable. In a15 ~rli*r rl~l cable TV l.~ ;r n~ the signal slope is ~osili~, when the signal leaves t~le ~mr1ifi~r At the end of the cable, the signal slope is ne~liv~;. In ~ tion~ sigr~al tr~n~mi~ n in the cable E~on~r~11y has a higher s.l~ ~.--,-I;on at the high L~ u~n~ end.

In the tap ~ -..hl~ of the invention, the signal ~ c~ of the tapped-off signal is 20 ~r~,fe.dbly field adju~ le without signal hlt~,.lu~ion. The invention permits the tap assembly to be de~;~.Fd to co~ , for non-~ ;ru~ cable ~ ;on, to provide a flat signal le~ e over the length of the cable, and flat signal ~Y~rArtis~n over the ltd high L~u~,.l~ and low L~ u~,n~"~ s~ u~ over the length of cable. Tlle d signAI ~ ,lg ll is tunable by ~e signal chip design and/or by adj u iLil~g the gap 25 between the signal chip and the center con~luctQr. The signal chip fimntion~ at least in part as a ~ ,.vmg ~ nnA The sig~al chip is ~ with m-11tirle cuu~lillg paths to ensure the l~.luiLed signal ~ L. Inductive and .-l~A~ ;v~ cuu~ling are more çffici~ont at higher L~u~i~. The ~ ;ple cou~lmg paths can be o~1;...;-- d to tA~e into accuu~lL
the cou~ lg çffiei~nry dirr.,.~.lces at the high and low L~ ;es The tapped-off signal 30 from a 1-~ 1 tap ~sembly is not b~1~nced in the signal ~ ,~ lh of the Lci.lu~
ulll. The ~l~,f~ ,d tap ~c~embly provides the adva"~ges due to the capability tobalance the signal ~

W 096~3q1?~ P~~ os6~4 The tap of the invention is preferably rleei ned to have a high selectivity for coupling the desired signal traveling in a first direction on the distribution cable, and to ~ reject rçflected signals which travel in an o~posile direction on the distribution cable. In pler~ d tap embo~ , the inductive coupling cancels one direction of the c~ v,~
5 coupling, thereby Pn~hling ~ction of the desired signal without reflected ghost signals.

A plefell~d embo~limPnt of the invention will be described with l~.,.e.lce to Figures 1-8. Figure 1 illu~ldtes a hinged c~ l-style tap hou~h g 100 which fits over a cable 1000 and l~,C~iV~S a tap ir~eert 20 (Figure S). ~ltho l~h a hinge 11 is illll~te~l thle 0 tap housing lQ0 can have two s~ e parts which are bolted together. The housing is pl~r~dbly f~hric~ted from a con-l.,el;ve and ele~,L,o.n~ ~lly ~;:hiP]~1ing m~t~ri~i. Th,e housing 100 ;.~ (les body halves lOa and lOb. The intPrn~l configuration of the bod~y halves lOa lOb preferably has a f~ Vb~ lly equal to the outer tli~mp~ter of the cable 1000 for an C.lVil~ lly and ele.,11v...~ lly tight fit. A body half inclllcles 5 a recess 14 Ihlvu~ which an ~,,kd signal chip 22 (Figure S) passes. In the ~l~,f~l~d embo~limPnt the recess 14 is shown as an elong~te lnl-g;l~ l recess. However, other suitable shapes may be used. The hml~in~ 100 is robust enough to round an out of roun~1 cable upon ti~htPnin~ of the housing 100 to the cable 1000. A way to achieve this effect is through the use of a harder metal alloy than the ~hiPl~lin~ layer on the coaxial cable 1000. The housing 100 ~ ihon~lly i~rl~les an ~lignin~ hole 12 into which am in~t~ tion tool S00 (Figure 2) is ins~,~d. The ~ ning hole 12 helps align and control the depth of a cut made into the cable 1000 ~ ou~L the recess 14 by the cutting tool 50Q.
However, any sllit~ble slLu~ e to permit rv....;..~ an opening in the outer co.~lu~ilo~ may be used.
The outside ~ ..--t~ - of a hard line ~i~ibution cable ranges from 1.016 cm (.400 in) to 3.810 cm (1.5 in). Sl~da..l cable si~s are, for e ~ ple, 1.046 cm (.412 in), 1.372 cm (.540 in), 1.588 cm (.625 in) and 1.905 cm (.750 in). A typical cable used for ilhl~tion of this invention is 1.372 cm (.540 in) (e.g., Co~ cope 540 cable). The body halves include passageways 16 to permit the tap h.. ~;l.g 100 to be se~ ly bolted around the cable 1000. The bolting operation forces the inner face 102 of ~e tap housing 100 against the outer con~luctQr of the cable 1000 to make el-octri~l contact b~;lw~ell the two sllrf~es. The inner face 102 of the housing 100 may include conta!ct elem~nt~ such as WO 96134428 PCr/U~ 74 .. ~ ,. . --7--piercing spikes 18a 18b 18c 18d which are driven into the outer colldw,tor of the cable 1000. Although four spikes are illù~ one spike is suitable if a good contact is formed b~ n the tap housing 100 and the cable 1000.

Distribution cables come in many dirr~ conflgllr~tion~ Generally the cables contain a center conA~lctQr surrounded by a ~ ctric region and a rigid outer con~ ctQr and, optionally, an outer electlri-~lly in~ tin~ cable l,lole~ilive jacket. In the event the distribution cable co.~ this outer in~ tin~ le~;live jacket, a portion of the p~ole~;live jacket is preferably len~ 1 prior to tl~ .g the housing 100. In ~ ;r~ d 0 embo~ , the in~ tin~ jacket is l~,.lwv~d from an area about the cable 1000 slightly longer than the lengdl of the O~.ll..g to be cut in the cable 1000. In pl~L..eclembo~ the in~ ting jacket is left intact on the cable 1000 in the areas CO..~ g to the t~vo end portions of the ho..~ g 100 to help form an e.~vilo....~
seal with the inner face 102 of the housing 100. The ~us~g 100 is sealed to the outer 5 surface ofthe cable 1000 by any ~;I;Jble means such as a mastic, adhesive or sealant, e.g.
an epoxy resin, or (to provide .c ~ "~.bility) sui~l~le gel or rubber ms-t~i~l~. r,Y ....~
of suitable gels include those ~le~l~.ribe~l in U.S. Patent No. 4,600,261 and US Patent No.
5,350,057, the ~ rlosllres of which are illCO ~alt;d herein by l~r~nce for all ~ul~oses, and the ms~t~ri~l~ available from Dow Corning under the trade name Sylgard~, in 20 particular Sylgard~ 527. Option~lly, ~l~,..no~lastic e~ ""-. sealing gels such as Sl l)to.l~ based :j~y.~,ne ~thylene-butycl~e-s~yrene and/or :jly~ e e ~ lene-propylene-styrene oil e~ h ~~(~P~1 gel m~t~ri~l~ can be used. These thermo~l~Lc gels are ~n.or~lly 1~~o to 20% by weight polymer and the rest to 100% an ~Alludel fluid. Optionally, th,e cr~ ked or the~noplastic gels can include up to 2.5% additives such as ~ntioxi-l~nt~:, 25 corrosion h~hibil.,.~, fim~ es~ and the like.

Figure 2 i11..~ s the tap housing 100 in~t~ d around the cable 1000 e.~yosin~gthe recess 14. The tap h.,..~ 100 firmly grasps and seals to the cable 1000 to provide a fixb~re for the inct~ tion tool 500 to make the cable cut. Any :~ui~ble in~ tion tool 30 can be used. A ~-ef._.-cd in~t~ tion tool 500 is ill~ id For eY~mrle a standard tool 510 is available from the Makita CO~o~alion as Model 9500D with the morlific~tion of the ~lignm~nt fixture 512. The fixture 512 is configured to cut an opening about .445 crn (.175 in) wide by about 3.810 cm (1.5 in) long. Larger ~ m~t~r cables provide the option CA 022l9l25 l997-l0-23 W O 96~34428 PCTnUS96/0S674 " , -8-to have a longer and/or vvider oper~ing. The longit~ in~l recess 14 is ~ Ç~ ,d to semi-circular cuts bee~-lee it is easier to seal and lirnits stray signal loss. This type of cut also helps locate and align the signal chip 22 (Figure 5) upon insertion. The cutting blade 514 is adapted for precise depth of cut into the outer conductor of the cable 1000. The depth will be a~out .508 cm (.20 in) for a 540 cable. Larger cables require a deeper cut bee~use the tliet~nre from the center con~uGtor is illl~lkllll to achieve proper signal reception and/or injecti~-n Figure 3 ill~ s an ~ ;vc ~,-.~ I;ve of a tap housing 100 ~ln~ d to the ~o distribution cable 1000. The inet~ tion tool 500 is ill,.~jl.. l~d with the ~lignm~nt pin 512 aligned for insertion into the ~lignm~nt hole 12 in the tap housing 100. The depth of the cable cut is controlled by the depth control face 516 on the in~ tinn tool S00 such that the cutting blade 514 cuts to a ~ d depth of about .508 crn (.200 in) for 1.372 cm (.540 in) hard line coaxial cable. Figure 4 illl.~ s the tool 500 i~ .ttd in the recess;
14 cutting into the distribution cable 1000 and ~ JU~ the ~ le~ ;c m~t~i~l 1020 toward the center co~ tor 1010. The depth control face 516 ~lu ,s on the tap housing 100 ta ensure that the cutting blade 514 does not contact the center ~du~ilol 1010. With the inet~ tion tool S00 ~lnrh~ the inet~ ti~m tool S00 is rotated toward the cable 1000 as illll~tetl by the arrow at the base ofthe tool S10 until the depth control face 516 bottoms onto the tap Luu~i~ 100.

After an o~ about .445 cm (.175 in) wide by about 3.810 cm (l.S in) long by about .508 cm (.200 in) deep is made in the cable, a tap insert 20, ill~ cl in Figure S, is ~ r~ l to the tap h..~ 100. The tap insert 20 inrhltles a tap face plate 21, a signal chip 22 and RF ports 24a 24b 24c 24d. The tap face plate 21 ~llnrll~s into the hvu~i~, 100 at fixiure points 17a and 17b on the housing 100. The tap face plate 21 is sealed to the housing by any slli~ble means 28 such as m~etire, epoxies, or for re cillt~.ability~
gel/rubber sealing m~t~i~le as previously deerr~ Preferably the tap face plate 21 is' bolted or SCl~ d I ~u~L holes 26a 26b to tapped holes 17a 17b in the tap housing lO0 to coll~ ss and ~ehi~lrlin~ seal thereto as illu~ e~l in Figure 6. Figure 6 i~ lale;s the tap housing 100 with the tap insert 20 inet~llçd on the cable 1000.

~ CA 02219125 1997-10-23 '~W O 96/34428 PCTrUS96/0S674 _9_ Figures 7 and 8 illl~ (es the signal chip 22 i~ e;d into the cable 1000 and ,es_,lL~ an inductive coupling as well as a c~ a~;l;ve coupling through which a resistor R b~l~nces the c~ vely coupled signals and inductively coupled ~ign~l~, thereb~ycou~ lg the direct signal and rejec,ting reflected signals. The main coll~ol~nt3 for the signal chip are a contlllctive path and a bAlAnrin~ resistor. The co~ ;ve path fimrtion~
as an ~ A to extract a portion of the signal from the center con~lllrtQr 1010. The ~-v~Ly of the 5~ A to the center CO~ 1010 means that it has both an inductive, and a cAl~cil;ve fimrtirl~ The p ~ .lce of a resistor 32 and ground 30 on the signal chip 22 allows the AntennA to have both inductive and c~ c;L;ve fiunctions Ol).,ldl~lg at the same tisne. By selecting the proper value of the resistor 32, a balanced sign~ (inductive and c~r~citive) ~-vill be e~rtr~cte~ and/or inserted, Thus, the ~ A becom~s selective by acc~L~g the source signal and rejecting reflected signals.

The signal chip 22 in the tap insert 20 inel~e~ an end Att~rhed to the RF ports 24a s 24b 24c 24d shown in Figure S a~r~ t;ly sized. The ~-~t~ A can have a size from about .635 cm (0.25 in) to tens of ce. .~ ;. . .et~ - ~ (inches) long. For coll~e~-ienr-e, a 1.524 crm (0.6 in) long Z~ A was used. The 5i.~t~ A iS ilhJ~ in Figures 7 and 8. The resistor R is adjusted to ensure rejection of reflec~ed signals. In a ~lef~ d embodiment illu~l.,.~ef1, the i..~t~ A has about .762 cm (.300 in) strAipht region 22a A~ r~.,l to the center con-lur,tor 1010 with ~dj~A~nt .762 cm (.300 in) radius 1/4 section curves 22b Oll either side ofthe strAight region ~a. These curves 22b are cc.l-nP~,~ed to .381 cm (.150 in~
st-Aight regions 22c and a final 1.524 cm (.600 in) s~ icil~ lar co~ e~ n region 22d for the pl~r~ d shape ofthe multi-turn ~ A

The .762 cm (0.3 in) flat section 22a ~1;A~ I the center con~ ctor 1010 is chosen to have a long section of the coil that could ~ve a close ~ r to the center con~ ctolr 1010 of the coaxial cable 1000. The longer the ;~ "~ on section ensures t_e ~l,U~c,L
the signal pick-up. The two 1/4 circles 22b at both ends of the .762 cm (0.3 in) straight line 22a are for smooth trAn~ition~ of the str~ight section 22a, so that a colll~a ;l mnltirle tur,n of coil is form~ The ~iul ~ lules of the trAn~ition sectors control the rç~etAnre of the coil. Smooth trAn~itions allow more turns on the coil to allow more signal pick-up. In this "l~,r. .l~d eYAmple, a six-turn-coil with the shape as illu~ çd creates a flat frequency ' W 096/34428 PCTrUS96/05674 le~ e for the pick-up signal. The coil Af~ei~n~cl may have Alt~mAtive shapes, as long as proper reAct~nre values are built in to balance the signal l~ s~ollse.

The 5i.1~ A iS screen printed on, for eY~mrle a printed circuit board to includ~e 5 the resistor for reflection çAnr~ tion The resistor R will have a value generally b~lw~e 10 and 500 ohms but any suitable reCiet~nce or v~iable ç~ c;~ e is to be used tocouple the signal out. In the described emboAim~nt, a 75 ohm resistor was found to ha~,~e best dh~,~,livily for signal al~ withdrawal. The signal chip 22 can be adjustable such that the Aiet~nre b L~ the center c~n~ ctQr 1010 and the h..l~ can be adjusted to 0 obtain a signal strength of about lOdBmV over the desired frequency range.

To i,ll~lo~, the signal strength of the ~ eA signal and to balance the signal aL~ lh at both high L~.lut;l~;y (UHF) and low frequency (VHF), the ~ A can be made in the form of a coil described above. The coil is l~esignr-l to extract the signals arld 15 to act as a r~tivt~ load to balance the signal pull off at high L.,~lue~;y and low L~ u~n~y. The coil could be a .043 cm (.017 in) thick (26 gauge) .~ ..e~;c wire wl~ d around a suitable nlal~&~,l with 1.52 cm (.6 in) AiAmrtrr and flat region as shown in Figure 7 which faces the center conAuct~r. The coil ~iiAmrter can be .254 cm (.1 in) to several c~ntim~terS (inches). The choice of about 1.52 cm (.6 in) is preferably chosen for 20 co...~ ee and signal reception. In order to ill~leaee the coupling streng~, mllltiple turns of the 0.6 inch pick-up cl3il have been chosen. In order to balance the pull off signal ~~ u~ncy r~apvnse and the CVU~1J11g çffi~;~o.nr.y, a 6 turn pick-up coil was cO~ uc~d.
For a 6 turn pick-up coil the e, I-~;~d signal al~ lh at high frequency is the same as tlle signal aL~ ,lL at low r~ u~.lc~, i.e. with 6 turns there is the ~l~rtll~d flat ~ vnse over 25 the desired fl~.lu~;~ range. More turns would provide a dowllw~d slope of ~ ;te~l signal while fewer turns would create an upward slope. To obtain the pl~f~l~d flat l~i,pvllse, the number of turns of the pick-up coil is adjusted to create a mirror image of the exieting signal strength along the cable.

Figure 8 is a s~ ;c of the inductive coupling 35 of the 5~nt~nn~ with t~he resistor adj~ - .1 32 and ground 30. The RF signal out is illustrated by 34 and c~ drain portisn is illllefr~tecl as 37.

W O 96/34428 -11- PCT/u'~ (c~74 The invention was used to insert a new tap into a TV distribution cable be~
two ope.~ lg taps, each c~nnectecl to a television set, without inl~.lu~ g any of the signals to the television sets. The new tap was cu...~ d to a television set and also received the TV signal.
The invention is useful in the system described in cOp~ , co..~ ..ly ~c.~
US Serial No. 08/353,541 filed December 9, 1994 and entitled Distributed Digital Loop Carrier System Using Coaxial Cable, the entire ~ sl1re of which is ~co~ lal~d herein by l~,r~ ce.

Claims

Claims What is claimed is:

1. A method of forming a tap into an intermediate point on a continuous coaxial cable comprising an inner conductor, a dielectric surrounding the inner conductor, and an outer conductor surrounding the dielectric, the method comprising the steps of:
a. forming an opening in the outer conductor of the coaxial cable;
b. forming a cavity in the dielectric under the opening; and c. mounting a tap insert to the coaxial cable, the tap insert comprising a signal chip, so that the signal chip is located in the cavity adjacent to the inner conductor of the coaxial cable, and can (i) extract signals from the inner conductor, or (ii) insert signals into the inner conductor, or (iii) do both (i) and (ii).

2. The method as claimed in claim 1, wherein steps (a) and (b) comprise:
i. fixing a tap housing around the coaxial cable, the housing, when so fixed, comprising:
ia. a first end portion, ib. a second end portion, ic. an intermediate portion having a recess, and id. an alignment element having a known spatial relationship with the recess;
ii. locating a cutting tool by means of the alignment element; and iii. operating the cutting tool through the recess in the tap housing.

3. The method as claimed in claim 2 wherein step (c) comprises attaching the tap insert to the intermediate portion of the cable tap housing.

4. The method as claimed in any one of claims 1 to 3 wherein the opening formed in the outer conductor and the cavity formed in the dielectric are elongate and longitudinal.

5. The method as claimed in any one of claims 1 to 4 wherein the tap insert ismounted so that the signal chip does not touch the center conductor of the coaxial cable.

6. The method as claimed in any one of claims 1 to 5 wherein the distance between the signal chip and the center conductor is adjusted to select a desired signal strength of an extracted signal.

7. A coaxial cable tap housing, suitable for use in the method of any one of claims 1 to 6, the tap housing comprising:
a. a first end portion, b. a second end portion;
c. an intermediate portion having a recess;
d. means for fixing the housing around an intermediate point on a continuous coaxial cable;
e. means for environmentally and electromagnetically sealing the tap housing to the coaxial cable.
f. an alignment element having a known spatial relationship with the recess;
and g. means for mounting a tap insert to the recess of the tap housing.

8. The tap housing according to claim 7 wherein the housing comprises hinged body halves.

9. The tap housing according to claim 7 or 8 wherein the means for environmentally sealing the tap housing to the coaxial cable comprises a mastic, an adhesive, or a gel.

10. A tap insert, suitable for use in the method of any one of claims 1 to 6, the tap insert comprising:
a. a tap faceplate comprising i. an inner face, ii an outer face, iii. means for mounting the tap faceplate to a cable tap housing, and iv. means for environmentally and electromagnetically sealing the tap faceplate to the cable tap housing;
b. a signal chip mounted on the inner face of the tap faceplate; and c. means for providing RF input and/or output, said means mounted on the outer face of the tap faceplate.

11. The tap insert according to claim 10 wherein the signal chip comprises a multi-turn antenna coil having a major portion located within the opening in the cable.

12. The tap insert according to claim 11 wherein the multi-turn antenna coil comprises a straight section adjacent the center conductor of the coaxial cable to provide capacitive coupling between the center conductor and the signal chip.

13. The tap insert according to claim 11 or 12 wherein the multi-turn antenna coil is comprised of a straight section adjacent the center conductor of the cable, 1/4 circle regions bounding the straight region, and a semi-circular region connecting the 1/4 circle regions as illustrated in Figure 7.

14. The tap insert according to any one of claims 10 to 13 wherein the signal chip comprises a resistor to permit the acceptance of the transmitted signal and rejection of the reflected signals.

15. The tap insert according to any one of claims 10 to 14 wherein, once installed, the signal chip does not touch the center conductor.

16. The tap insert according to any one of claims 10 to 15 wherein, once installed, the distance between the signal chip and the center conductor is adjustable.

17. A kit of parts for forming a tap into a coaxial cable, the kit comprising:
a. a coaxial cable tap housing capable of attaching around an intermediate point in a continuous coaxial cable; and b. a tap insert comprising a signal chip, the tap insert capable of attaching tothe tap housing after an opening has been made in the outer conductor, and a cavity has been made in the dielectric, of the coaxial cable.