Fortune7

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

Mac_Man_UK

Hi Andy, its an FCC requirement that "Frequency determining components" are not allowed to be adjusted unless you are a qualified person ( or something along those lines).

In the UK, we have 10 KHz channel spacing, whereas in the USA they are on 20 KHz spacing with Primary Users interspersed between the channels. Hence the criteria to be more tight.

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.

Hope that makes sense......

Fortune7

Thanks Mac_Man_UK: yes, very helpful!

So with the standard (72MHz) module and crystal(s), what benefits are there in having the module sent in and re-tuned? Does it get tuned to just one crystal and (therefore) other crystals used with it are less likely to be in-tune, or does the tuning cover all channels equally? I guess I'm trying to find out whether its better to swap MODULES with their crystals factory-tuned to them or are there disadvantages in just swapping crystals as I've been doing?

Thanks again

Andy

Mac_Man_UK

Getting the older style modules tuned with their crystal has the advantage of having the module frequency set to the exact channel frequency. Each Xtal will be slightly different, they have a spec to match which here in the UK is +/- 10 ppm ( parts per million ). I don't know what the US specs are for their Xtals but would imagine the same. Therefore a brand new UK Xtal at 35.5 MHz could be off by +/- 355 Hz, so a US Xtal runing at 72 MHz could be off by +/- 720 Hz. Plus, each Xtal will have a slightly different "pullability" ( for want of a better word ). i.e. When a DC voltage is applied the frequency shift may not always be identical for each Xtal. Every module & Xtal that I get in is always checked for its centre frequency, deviation and shape.

In all honesty, now that you have moved over there and now come under the FCC regulations, the safest bet is to get a Synth Module unless you are only going to stick to one channel for flying. You've been spoilt in the UK with its ability to swap Xtals willy-nilly...

[8D]

Fortune7

Thanks again Mac_Man_UK - very helpful and I can now make a truly informed decision about the synth. module. Can I assume it will work with crystaled standard receivers or must it always be used with the new "synth" Rx?

Andy

Mac_Man_UK

The Synth module will work with any JR receiver. No requirement to go and buy synth receivers unless you are changing frequencies a lot.


[8D]