I've been swapping crystals in the X347, X388, XP8103 and now XP9303 for years and have had no discernable issues. However, following a recent heli crash where the R7700 Rx went into failsafe on PCM I'm wondering if the module is particularly tuned to the crystal it's supplied with. I'd changed the crystal from the one originally supplied in the module, for a different channel (supplied by Horizon Hobby). I'm originally from UK and noted when I moved to USA and bought a new module for 72MHz, the crystal was 'glued' in with hot-melt glue which was removed without difficulty. Is this an American FCC requirement or is it JR's preference to keep a crystal with a module for life, or until it's re-tuned?

I'm getting into Jets and want to ensure I have the best 'match' of crystal and module. I see people are referring to 'sending in the radio for re-tuning'; how important is this for the best range? If it's recommended, how does the new synth. module with matching Rx manage to cope with calibration across the entire range of channels?

Thanks

Andy

Hi Andy,
I believe swapping crystals is not a good idea if you want the very best R/F link you can get. Personally I can't afford to chance a poor R/F link causing a crash that otherwise could be avoided. I would suggest sending transmitter & receiver in for proper tunning when switching channels. Also it's a good idea to have the service center re tune & align your receiver if you plan to use a loaded whip antenna.

On to your second question as to the JR synth modules calibration across the entire range of channels. A very good question.. to which there is no answer other than to say there is some variation. I recommend doing a very careful range check... Baseline and powered up on whatever channel you dial in.

NOTE: From my preliminary testing I have found that the JR synth. transmitter module (one only tested so far) has about 10% more R/F output than any of the crystal controlled modules I own or have tested over the past several years. Why? I'm not sure other than to say transmitter output is kING, possibly it was designed with higher output to compensate for the variations from high to low channel selection to keep a strong R/F link between the synth transmitter module and synth receiver modules! My relative R/F output test.. is a simple one, but a test that does directly correlate to shorter or farther distance in range checks... given the same receiver and aircraft setup!
Lee H. DeMary
AMA 36099

Thanks, Lee - very helpful!

I took the liberty of posting the same question on the JR Radio support forum and the UK JR support guy replied with (In response to the issue about calibration of the synth module):

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The new synth modules are much more accurate than the Xtal's and have a wider passband on the RF output. Effevtively this means that the RF signal is tighter in its Occupied BandWidth yet with the ability to be used over the full channel range available.
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Maybe this helps explain the difference in RF output??

Anyway thanks again - I guess I'm trying to find out whether I shopuld carry-on occasionally swapping crystals or to have 'tuned' modules, each on a set channel or wheter it's better to go for the synth module and matching Rx. From the responses so far (including yours) it looks like the synth module is the way to go. I do recognise the issues associated with 'easy' channel changing though....

Andy

Andy,
Check out the other thread about the JR receiver / transmitter module... some good points being made. Glad to here about the narrow / precise frequency control of the synth module... I can confirm a slightly higher output.... and the more the better.. as long as it is on frequency.
Lee