US2084740A - Filter circuit - Google Patents

Filter circuit Download PDF

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Publication number
US2084740A
US2084740A US59858A US5985836A US2084740A US 2084740 A US2084740 A US 2084740A US 59858 A US59858 A US 59858A US 5985836 A US5985836 A US 5985836A US 2084740 A US2084740 A US 2084740A
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United States
Prior art keywords
circuit
harmonic
inductance
line
capacitance
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US59858A
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English (en)
Inventor
Lewis J Mckesson
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
RCA Corp
Original Assignee
RCA Corp
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Filing date
Publication date
Priority to BE419527D priority Critical patent/BE419527A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US59858A priority patent/US2084740A/en
Application granted granted Critical
Publication of US2084740A publication Critical patent/US2084740A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H2/00—Networks using elements or techniques not provided for in groups H03H3/00 - H03H21/00
    • H03H2/005—Coupling circuits between transmission lines or antennas and transmitters, receivers or amplifiers
    • H03H2/006—Transmitter or amplifier output circuits

Definitions

  • This invention relates to electrical systems and especially concerns auxiliary equipment associated therewith for preventing undesired currents from affecting said systems and associated apparatus.
  • filter circuits usually in the form of low pass filter arrangements, may be used to suppress separately each of the undesired harmonic frequencies, but such arrangements, in
  • the above mentioned difficulty is overcome in the present invention which provides a circuit utilizing the same inductances and capacitances to resonate at specified frequencies. In this manner the number of reactances used is reduced as compared with other circuits having the same electrical characteristics.
  • the present invention is particularly effective in high power radio transmitters which for the most part employ two ormore vacuum tubes in push-pull relationship, the output of which is coupled to a transmission line which is balanced to ground.
  • the second as well as other even harmonic voltages is present on the transmission line as a push-push voltage, that is, the voltage is zero across the line and maximum between each line and ground.
  • the third, as well as other odd harmonic voltages on the line appears as a push-pull voltage where the voltage is 180 maximum across the line.
  • a circuit arrangement which provides, theoretically, infinite attenuation for second and third harmonic voltages, and is also highly effective in suppressing higher harmonic voltages.
  • Fig. 1 illustrates, schematically and by way of example only, the harmonic filter circuit of the invention as applied to a high frequency radio 5 transmission line circuit;
  • Fig. 2 is a graph illustrating the effectiveness of the lter of the invention on the second and third harmonic frequencies
  • Figs. 3 and 4 show modifications of the harmonic filter circuit of the invention.
  • FIG. l there is indicated diagrammatically in box I, a conventional type of pushpull power amplifier stage of a radio transmitter with which there are associated a pair of vacuum tubes and an output or tank circuit 2. Since the transmitting circuit forms no part of the present invention per se, and is of a type well-known in the art, no detailed description thereof will be given.
  • Tank circuit 2 is inductively coupled to coil 3, which is associated with an antenna system 4 through transmission line 5 and filter circuit B.
  • R2 Connected to the center of coil 3 is a high resistance R2 which also connects with the anode supply for the transmitter tubes, as shown.
  • a pair of blocking condensers C3, C4 Serially connected in the transmission line circuit 5 are a pair of blocking condensers C3, C4 of negligible impedance to the high frequency currents which prevent direct current from the positive terminal of the anode source of supply from entering the filter and antenna circuits.
  • Resistor R2 functions to maintain coupling coil 3 at the transmitter direct current anode potential to prevent arcing from the tank coil 2 to the coupling coil 3, a condition which would otherwise occur due to leakage across the transmission line blocking condensers C3, C4.
  • Inductance coils L1 and L2, generally known as drain coils, are of high impedance to the high frequency voltage and serve to maintain the antenna and lter circuits at ground potential for direct currents. 50
  • the filter circuit of the invention for suppressing second, third and higher harmonic voltages, and for enabling the desired degree of coupling between antenna and transmitter is shown between the two vertical dot and dash lines and labeled 6.
  • Reactance coils La, Li, L5 and Le are adjustable and give the desired degree of coupling between line 5 and coil 3. Since the second harmonic voltage, indicated as 2j in Fig. 2, is present as a push-push voltage on the transmission line, and the third harmonic voltage, indicated as 3f in Fig.
  • Adjustable capacitances C5 and C6 and adjustable reactance coils L7, Ls and L9 are cmployed to achieve this result.
  • Coils L7 and Ls may, for convenience, be combined to form a single coil whose mid-point connects with L9.
  • a capacitance C7 may replace inductance coil L9, as shown in Fig. 3. The choice between an inductance L9 or a capacitance C7 will depend on the constants of the other impedances in the circuit.
  • the invention is not limited to the arrangement of inductances and capacitances shown in Figs. l and 3, since these may be changed to the arrangement illustrated in Fig. 4.
  • electrically the filter of Fig. 4 is the same as those of Figs. 1 and 3, the system of Fig. 4 may, in some instances, have practical advantages over the other arrangements.
  • the transmitter l In setting up the filter circuit, the transmitter l is first properly loaded in known manner by matching the impedance thereof with respect to the line 5. This is done by means of coils Ls, L4, L5 and La, and a mid-shunt capacitance C8 used to replace C5, C6, L7, La and L9 temporarily during adjustments.
  • the shunt tuning circuit consisting of C5, Ce, L7, Ls and L9 is connected across the line replacing the temporary capacitance;
  • Filter 6 may be tuned to suppress the harmonics in the following manner:
  • a selective receiver is first set up which is equipped with an output meter for indicating Volume, and the receiver tuned to one of the harmonic frequencies in the transmitter system, let us say the third harmonic.
  • a Wavemeter may be used instead of the receiver, but the wavemeter is generally not as satisfactory as the receiver.
  • the second harmonic circuits are now resonated by varying coil L9 whose adjustment will have no effect on the third harmonic trap tuning.
  • the inductance of coils L7 and La may be reduced by employing a short-circuiting strap indicated by dotted lines S. This strap is symmetrically connected to the coils L7 and Ls with respect to the junction point to which coil L9 connects, in order that the second harmonic tuning be not affected.
  • the tuning of the filter circuit t will be correct when (a) the load on the power amplier transmitter circuit l is resistive only, and (b) the impedance of the output circuit is such that the power amplier is loaded to the desired value.
  • Condition (a) will exist when the tuning of tank circuit 2 is very nearly the same with the transmission line 5 connected or disconnected from coil 3. When both of these conditions (a) and (b) are satised, the power amplifier efficiency will be a maximum for a given amount of loading.
  • the filter circuit of the inn vention provides a greater attenuation for the second harmonic voltage than certain circuits heretofore employed, inasmuch as the midshunt section C5, C5, L7, La, L9 is practically equivalent to two circuits in parallel as compared to a single circuit.
  • Another advantage is that the iilter provides a Very large attenuation for the third harmonic voltages, and more attenuation on higher harmonics than obtained in previously used circuits.
  • the amplitude of the third harmonic was reduced from 37 niicrovolts to less than .5 microvolt, corresponding to a 45 decibel reduction. Equivalent results were obtained on second harmonic reduction.
  • Fig. l sets forth, by way of example only, values for the constants which may be used in a harn monic filter circuit associated with a short wave transmitter system adapted to function cn 4535 kc.
  • the filter provides maximum attenuation to the second and third harmonic voltages and, in addition, acts as an impedance matching circuit between the transmitter I and antenna transmission line 5.
  • the calculated and actual values dc not agree very closely in a filter of this type when mounted in or near shielding becausev of the diiiculty of estimating or calculating stray capacities and mutual impedances, especially at high frequencies.
  • the input and output impedances are known only approximately so the actual circuity values are best determined by trial and erro-i" after the approximate values are known.
  • an, antenna an exciter circuit comprising a pair of push-pull electron discharge devices, a transmission line connected between said exciter circuit and said antenna, and a harmonic iilter circuit coupled to said transmission line, said lter comprising a series circuit of capacitance, inductance and capacitance, in the order named, connected in shunt to said line, said series circuit being tuned to resonate at the third harmonic voltage of the fundamental of said exciter circuit, and a variable connection to groundirom the electrical center of said inductance.
  • a short wave radio transmitter having a power ampliiier comprising a pair of push-pull electron discharge 'devices, of a load and a two wire transmission line connected between said load and ampliiier, a pair of adjustable coils in series in each side of said line for matching the impedance of said transmitter, and a series circuit of capacitance, inductance and capacitance, in the order named, connected between the junction point of one of said pairs of adjustable coils and the junction point of the other pair of adjustable coils, said last series circuit being tuned to resonance at the third harmonic voltage appearing in said line, and an adjustable reactance connected be'- tween ground and the inductance of said last series circuit for attenuating the second harmonic voltage appearing in said line.
  • an antenna an exciter circuit comprising a pair of push-pull electron discharge devices, a transmission line connected between said exciter circuit and said antenna, and a harmonic filter circuit coupled to said transmission line, said filter comprising a series circuit of capacitance, inductance and capacitance, in the order named, connected in shunt to said line, said series circuit being tuned to resonate at the third harmonic voltage of the fundamental of said exciter circuit, and a connection to ground from the electrical center of said inductance, said connection including a variable reactance.

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US59858A 1936-01-20 1936-01-20 Filter circuit Expired - Lifetime US2084740A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
BE419527D BE419527A (enrdf_load_stackoverflow) 1936-01-20
US59858A US2084740A (en) 1936-01-20 1936-01-20 Filter circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US59858A US2084740A (en) 1936-01-20 1936-01-20 Filter circuit

Publications (1)

Publication Number Publication Date
US2084740A true US2084740A (en) 1937-06-22

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Application Number Title Priority Date Filing Date
US59858A Expired - Lifetime US2084740A (en) 1936-01-20 1936-01-20 Filter circuit

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US (1) US2084740A (enrdf_load_stackoverflow)
BE (1) BE419527A (enrdf_load_stackoverflow)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1176723B (de) * 1959-04-08 1964-08-27 Preh Elektro Feinmechanik Schaltungsanordnung bei Fernseh-Tunern zur Bedaempfung einer Oberwelle
US4261053A (en) * 1979-04-02 1981-04-07 Satellite Business Systems PSK Modulator with reduced adjacent channel interference
US4334203A (en) * 1980-04-09 1982-06-08 Broadcast Electronics, Inc. Second harmonic suppressor for power amplifier tank circuit
US4373581A (en) * 1981-01-19 1983-02-15 Halliburton Company Apparatus and method for radio frequency heating of hydrocarbonaceous earth formations including an impedance matching technique
US4433315A (en) * 1981-11-24 1984-02-21 General Electric Company Tunable coupling network
US4717896A (en) * 1985-03-21 1988-01-05 And Yet, Inc. Balun
US20090039975A1 (en) * 2005-04-07 2009-02-12 Conti Temic Microelectronic Gmbh Electrical Multiple-Wire System for Push-Pull Signal Transmission With an Attenuating or Filtering Element and Data Transmission Bus
EP2750291A3 (en) * 2012-12-27 2017-02-01 Renesas Electronics Corporation Semiconductor device and adjustment method of filter circuit

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1176723B (de) * 1959-04-08 1964-08-27 Preh Elektro Feinmechanik Schaltungsanordnung bei Fernseh-Tunern zur Bedaempfung einer Oberwelle
US4261053A (en) * 1979-04-02 1981-04-07 Satellite Business Systems PSK Modulator with reduced adjacent channel interference
US4334203A (en) * 1980-04-09 1982-06-08 Broadcast Electronics, Inc. Second harmonic suppressor for power amplifier tank circuit
US4373581A (en) * 1981-01-19 1983-02-15 Halliburton Company Apparatus and method for radio frequency heating of hydrocarbonaceous earth formations including an impedance matching technique
US4433315A (en) * 1981-11-24 1984-02-21 General Electric Company Tunable coupling network
US4717896A (en) * 1985-03-21 1988-01-05 And Yet, Inc. Balun
US20090039975A1 (en) * 2005-04-07 2009-02-12 Conti Temic Microelectronic Gmbh Electrical Multiple-Wire System for Push-Pull Signal Transmission With an Attenuating or Filtering Element and Data Transmission Bus
US7772938B2 (en) * 2005-04-07 2010-08-10 Conti Temic Microelectronic Gmbh Electrical multiple-wire system for push-pull signal transmission with an attenuating or filtering element and data transmission bus
EP2750291A3 (en) * 2012-12-27 2017-02-01 Renesas Electronics Corporation Semiconductor device and adjustment method of filter circuit

Also Published As

Publication number Publication date
BE419527A (enrdf_load_stackoverflow)

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