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TX Crystal in a Receiver

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Old 12-24-2004, 06:52 PM
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norbe
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Default TX Crystal in a Receiver

Very easy question, I think I know the answer, can I use a TX crystal in a receiver?
Thanks
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Old 12-24-2004, 07:43 PM
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Default RE: TX Crystal in a Receiver

No
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Old 12-24-2004, 08:35 PM
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Default RE: TX Crystal in a Receiver

Ok i thought the answer was yes, after all a crystal si a crystal what is the difference from a tx one and a Rx one technicaly speaking?
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Old 12-24-2004, 09:23 PM
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Default RE: TX Crystal in a Receiver

There are many differences. For one, the Rx xtal will be at least 455Khz away from the Tx freq (and as much as 11Mhz different). Other differences include, but are not limited to, the overtone mode used, capacitance, and pullability.

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Old 12-24-2004, 09:48 PM
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4 stroken ron
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Default RE: TX Crystal in a Receiver

Well, we used to do that about 20 years ago.........when I was racing RC cars...........on 27.........AM. Occasionally we might run into a freq. conflict, and one of the competitors would announce he would use his "secret" freq.[X(][X(] Everyone turned there heads so they did not see and the racer would change his Xstals. It seemed to work then. I guess things are different now
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Old 12-25-2004, 02:39 AM
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Default RE: TX Crystal in a Receiver

If I don't recall wrong there is a place that exchanges the crystals what was it?
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Old 12-25-2004, 07:11 AM
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Default RE: TX Crystal in a Receiver

The racer probably had a pair (tx and rx), and changed both. After all, it would do no good to just swap one of the two crystals.
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Old 12-25-2004, 10:09 AM
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4 stroken ron
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Default RE: TX Crystal in a Receiver

ORIGINAL: norbe

If I don't recall wrong there is a place that exchanges the crystals what was it?
http://members.aol.com/davthacker/ra...alexchange.htm


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Old 12-25-2004, 10:13 AM
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Default RE: TX Crystal in a Receiver

ORIGINAL: piper_chuck

The racer probably had a pair (tx and rx), and changed both. After all, it would do no good to just swap one of the two crystals.
Ah no. What he was doing was putting the Rx Xtal in the Tx, and the Tx Xtal in the Rx. It worked way back them, on AM 27.
[sm=confused.gif][sm=confused.gif][sm=confused.gif]
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Old 12-25-2004, 09:20 PM
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Default RE: TX Crystal in a Receiver

It could work today if you are using a single conversion receiver. Only one problem: Its illegal- as it was on the 27MHZ systems. With a double conversion receiver the crystals are too far off frequency for the system tuning to work.
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Old 12-26-2004, 09:50 AM
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Default RE: TX Crystal in a Receiver

Dirtybird, I doubt if it would work today even with single conversion as the transmitter crystals are usually approximately 1/3 the frequency of the final frequency (the transmitter operates on third overtone) while the receiver circuitry does not.
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Old 12-26-2004, 11:25 AM
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Default RE: TX Crystal in a Receiver

One thing I don't understand is how and why, technicaly, does the trasmitter have a third of offset. Shouldn't it be at the same frequency? Wouldn't it be better?
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Old 12-26-2004, 11:43 AM
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Default RE: TX Crystal in a Receiver

ORIGINAL: Rodney

Dirtybird, I doubt if it would work today even with single conversion as the transmitter crystals are usually approximately 1/3 the frequency of the final frequency (the transmitter operates on third overtone) while the receiver circuitry does not.
I think they are actually fifth overtone. Its hard to make a crystal of more than 15 mhz as they get too thin and fragile. For that reason the receiver also must be of the overtone type. Although they may not be the same type of cut which would make them incompatible
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Old 12-26-2004, 12:21 PM
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Default RE: TX Crystal in a Receiver

most recievers are dual conversion type which means that the first xtal is 10.7mhz away from transmitter freq. the next conversion converts signal to 455kc. the reciever xtal is 455kc away fron the transmitter freq. therefore they are not interchangeable.
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Old 12-26-2004, 05:01 PM
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Default RE: TX Crystal in a Receiver

Dirtybird, you are correct on most of them using 5th overtone, I am not sure what the receivers use but probably similar due to the frequencies involved.
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