All about Amateur Television - ATV. Ham Radio with Vision
Hosted by Tom O'Hara W6ORG - Email:
Retired owner of P.C. Electronics, The Leader in Amateur Television Equipment for 50 years - history
Sorry, but we do not have any of the older P. C. Electronics 70cm transmitter crystals, but we do have some misc. ones as listed at the bottom of this web page.
All P. C. Electronics 70cm ATV transmitters use plug in crystals that take the HC-49U or HC-50U holder, series resonant, 5th overtone, 50 ppm, Fxtal=Fout÷4.
439.25 MHz = 109.8125 MHz crystal
434.00 MHz = 108.5000 MHz crystal
427.25 MHz = 106.8125 MHz crystal
426.25 MHz = 106.5625 MHz crystal
421.25 MHz = 105.3125 MHz crystal (requires VSB filter on the TX output).
The 33cm transmitters are divided by 8 and the 23cm are divided by 12.
For other transmitters, downconverters and receivers, find the crystal frequency as determined by the formula on the respective equipment data sheet or manual.
A good source for buying one crystal at around $43, but you must send the order in British Pound Sterling by mail or credit card by PayPal, is QuartSLab. There are two US manufacturers that we found that can make the crystals in a HC-49 or 50 plug-in holder - Bomar Crystal type BC5EED5SR-XF and Cal Crystal - but they are $50 ea. and have a $100 minimum order. You might want to get another ham to go in with you if you only need one.
Transmitter or crystal controlled downconverter stop operating?
Crystal oscillators can age and change tuning due to to contaminents, moisture, etc., so before you order a new crystal, try repeaking the oscillator stage trimmer cap with a DC Voltmeter at the oscillator test point. Visually check the oscillator inductor, L1, to make sure adjacent turns are not touching - you should be able to slide an Xacto knife blade inbetween each turn. If that doesn't work, unplug the crystals and check the resistance with respect to ground, at the ground or relay side of the crystal socket with an Ohm meter. If the unit is a two frequency one, it may just be that the relay contacts have some oxide build up above a few Ohms which prevents the oscillation.
If this is the case, get a 10 Ohm 10 Watt resistor from Radio Shack - 271-132. Unplug the crystals. Plug one end of the resistor into the relay side of the crystal socket you are cleaning - careful not to connect to the oscillator transistor base side. Turn on the transmitter. Clip lead the other side of the power resistor to the +13.8V and quickly flip the F1/F2 switch back and forth a few dozen times and then disconnect before your fingers get too hot to handle the resistor. Repeat with the relay side of the other crystal socket. This will put about an amp of DC current through the relay and as it makes and breaks, will burn off the oxide layer that has built up. Repeak the oscillator trimmer cap, C1. Parts aging and contamination, expecially if the user is a smoker, can cause the trimmer cap plates to be come coated with foreign matter and change capacity.
Last update July 6, 2018 SCROLL DOWN
|Used In Model||Product Output Frequency|
|68.6250||1||TXTV Exciter board||1289.25 MHz ATV - use with|
144 in / 1296 out transverter
|70.0000||3||TXTV Exciter board||1265.0 MHz ATV - use with|
144 in / 1268 out transverter
|115.156||2||TXA5-33 transmitter||921.25 MHz|
|79.8333||1||TVCX-70 downconverter||433.25 MHz to 45.75 MHz IF|
|79.1667||1||TVCX-70 downconverter||429.25 MHz to 45.75 MHz IF|
|80.0458||9||TVCX-33 downconverter||914.8 MHz to 45.75 MHz IF|
|79.7500||3||TVCX-33 downconverter||911.25 MHz to 45.75 MHz IF|
|109.2500||1||TVCX-23 downconverter||1265.0 MHz to 45.75 MHz IF|
|111.2500||2||TVCX-23 downconverter||1289.25 MHz to 45.75 MHz IF|
|90.8125||1||TVCX-23 downconverter||1265.0 to Ch 7|
|92.8333||1||TVCX-23 downconverter||1289.25 MHz to Ch 7|
|92.3333||2||TVCX-23 downconverter||1253.25 MHz to Ch 8 or 1277.25 to Ch 10|
|90.3125||1||TVCX-23 downconverter||1265.0 to Ch 8|
|88.3333||2||TVCX-23 downconverter||1253.25 MHz to Ch 10|
|88.8333||5||TVCX-23 downconverter||1253.25 MHz to Ch 9|
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