|Publication number||US2296882 A|
|Publication date||Sep 29, 1942|
|Filing date||Jan 15, 1941|
|Priority date||Jan 15, 1941|
|Publication number||US 2296882 A, US 2296882A, US-A-2296882, US2296882 A, US2296882A|
|Original Assignee||Emerick Toth|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (5), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
E. TOTH Sept. 29, 41942.
CRYSTAL BRIDGE CIRCUIT FOR RADIO AMPLIFIERS Filed Jan. 15, 1941 GRID RE TURN INVENTOR Emerz'ck 76% BY ATTOR Y Patented Sept. 29, 1942 OFFICE' 2.29am CRYSTAL names CIRCUIT FOR RADIO AMPLIFIERS Emerick Toth, Cheverly, Md. Application January 15, 1941, Serial No. 374,439 4 Claims. (Cl. 173-44) (Granted under the act of March 3, 1883, as amended Apriiso', 1928; 370 o. G. 757) This invention relates toa crystal bridge circuit for R. F. or I. F. amplifiers and has for its object to provide a bridge'circuit which will eliminate the serious detuning normally caused between the input and output transformers in I the usual crystal bridge circuits when the transformers are aligned, either with crystals out and crystals subsequently switched into the circuit, or when the transformers are aligned with crystals in and the crystals are subsequently switched out of the circuit.
The single figure of the drawing matic view showing the circuits involved.
In the drawing reference character Ti-indicates a crystal circuit input R. F. or I. F. transformer. T2 is the crystal circuit output R. F. or I. F. transformer. L1 is the primary and L2 is the secondary of transformer T1, La and L4 being the primary and secondary respectively of transformer T2. The bridge circuitcomprises two 1 branches, one of which contains crystal X'I'L1 and the other of which contains crystal XTLe.
The two crystals are usually 50 to 500 cycles apart in frequency in order to give a band-pass filter effect to thecircuit. S1 is a double-pole, double-throw switch which is provided for the purpose of switching the crystals either in or out of the circuit. Condensers C1 and C2 are provided according to the invention in order to introduce into the branches of the circuit the proper coupling capacities to prevent detuning is a diagramwhen the crystals are switched either in or out of the circuit following alignment of the transformers with the circuit in the opposite condition.
At the resonant frequency of either of the two crystals the secondary of T1 is fairly tightly coupled to the primary of T: if condensers C1 and C2 are not present, although 100% coupling will not be achieved. Tight coupling at frequencies other than the crystal frequencies is prevented mainly by the capacity present in the crystal holders. With the switch S1 in the crystals out position the coupling between the two transformers is approximately 100% if condensers C1 and C2 are omitted. If the two transformers are aligned with S1 in this position serious mistuning .will occur if the switch is then shifted to the B or crystals in position, due to the introduction of the crystal holder capacity and the resonant crystals. Likewise, serious mistuning will occur if the alignment is accomplishedwith the switch on the B or crystals in position and the crystals are subsequently switched out of the circuit.
I The addition of condensers C1 and Cz serves to provide the proper coupling capacity with the crystals -in the circuit, fora degree of coupling comparable to that utilized in the transformers to obtain the desired band width with the crystals out of the circuit. It is thus impossible to .exceed the degree of coupling between the secondary of T1 and the primary of T2 determined by C1 and C2 and the variation in coupling caused by switching .from the A to B position is greatly reduced.
In addition, the selectivity curves resulting from the entire circuit are much more symmetrical, since in the A position C1 and C2 provide the proper degree of coupling for operation without crystals and in the B position the proper coupling is obtained at the resonant frequency of the crystalawhile the cap'acityeflects of the crystal holders, arising at frequencies ofi crystal resonance are minimized by the relatively small series capacities of C1 and C2.
The use of single condensers in the same man'- ner is applicable to single crystal operation. Typical values for. kc. operation are as follows: Cl =C2 10 mmf., L1 L2, L3 and L4 1 millihenry.
While the disclosure has been restricted to a single embodimentwhich applicant now considers to be the preferred form of the invention, the scope of the invention is to be considered as restricted only by the scope and limitations of the appended claims.
The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
1. A crystal bridge circuit comprising two branches, a plurality of coupled resonant elements in said circuit, a crystal in-each of said branches, said crystals being resonant at differ- I ent frequencies,'means for switching said crystals into or out of said circuit, anda capacitorin each of said branches between said crystal and the input end of said circuit, said capacitors providing approximately critical coupling be.- L tween said elements in order to substantially prevent detuning of said circuitwhen said crysin series with said crystal and located between said crystal and the input end-oi said circuit, said capacitor providing approximately critical cou-,
plins between said elements in order to substancuit subsequent to its alignment in the alternate condition.
3. A crystal bridge circuit comprising a crystal,
a pluralityioi coupled resonant elements in said" 10" circuit, means for switching said crystal either,-
into or out 0! said circuit. and means introducing into said circuit a capacitance in series with said crystal of such value as to provide approximately critical coupling between said elements to substantially prevent detuning of said circuit when said crystal is switched either into or out of said circuit subsequent to its alignment in the alternate condition.
4. A crystal bridge circuit comprising two branches, a plurality of coupled resonant eletlally prevent detuning 0! said circuit when said 5 crystal is switched either into or out of said cirments in said circuit, a crystal in each of said branches, said crystals being resonant at different frequencies, means for switching said crystals either into or out of saidcirouit, and
means'introducing into each of'said branches a capacitance in series with its crystal 01' such value as to provide approximately critical coupling between said elements to substantially prevent detuning 01'- said circuit when said crystals are switched either. into or out oi' said 'cireuit I01- EMERICK TOTH.
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US2755376 *||Jan 8, 1952||Jul 17, 1956||Csf||Crystal mixing device with wide frequency band|
|US2878454 *||Sep 3, 1953||Mar 17, 1959||Motorola Inc||Piezoelectric crystal filter|
|US3737814 *||Oct 6, 1971||Jun 5, 1973||Hughes Aircraft Co||Crystal filter circuit with sharply defined passband edge|
|US3783418 *||Jan 4, 1973||Jan 1, 1974||Johnson Electronics Inc||Crystal filtering device|
|US4554678 *||Dec 13, 1982||Nov 19, 1985||Honeywell Inc.||Wireless receiver having crystal filter at outputs of preamplifier|
|U.S. Classification||333/188, 330/174, 455/339, 330/167|
|International Classification||H03H9/00, H03H9/54|