Change Receiver Crystal

Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

No problem.

Just make sure you get a crystal that is compatible HiTec AND make sure your transmitter is on channel 12.

Now for the "legal" part - Unless you are a certified technician, it is illegal to change the transmitter crystal.

Real world - people change transmitter crystals with no problems.

IF you need to go with the "real world" option for the transmitter, make sure you do a range check.

I'm no expert, but I seem to recall reading (here) that a jump that large would be a problem, without sending it in to have it retuned.

Could you settle with a smaller jump?

Probably worth adding the words

In the USA to the start of that.

It's not illegal outside the US to change crystals.

IMHO that is a small jump. I say put the crystal in and range test it. mk

No problem. Hitech receivers have been sold since day one without a specific crystal. I have used them for 20 years with any crystal I need to match Futaba transmitter.

On Tue, 2 Oct 2007 17:24:18 -0500, "MJKolodziej" wrote in :

Agreed.

The folks who advertise that jumps are ill advised are one brand only (Futaba? JR?).

They divide the channels into a low range (11 to ... 36?) and a high range (36? to 60), I believe.

25 to 12 is in the low range. It should work OK.

Let us know how it turns out! I prefer to learn from your mistakes, if at all possible. :o)

Marty

In the last month I've changed RX crystal in two Hitec RX without problem. I "believe" there is a note in the Hitec crystal packaging that states using Hitec crystals in Hitec receivers requires no "tuning" at all.

Ray

On Tue, 2 Oct 2007 22:09:54 -0400, "RayB" wrote in :

That squares with my experience.

BUT Red's post got me thinking ...

I ***think*** that the warning about some systems being tuned for high or low parts of the 72 MHz band applied to TRANSMITTERS.

The manufacturer (Futaba? JR?) said that they tuned some circuit to optimize the output for one part of the band or the other, so that folks should not change the TX module out of the high or low range without getting the TX retuned by a certified professional.

It's a different case from changing RX crystals.

Sorry for any confusion that I may have introduced ... Marty

Well--actually a receiver front end can be tuned to work best on a specific channel or small group of channels. This depends on the receiver design, naturally. Usually, a receiver is tuned for stability, not for a narrow bandwidth in order to compensate for such things as temperature changes.

in :

I have a bunch of Hitec flite packs which I bought from Servo City . I asked them one time about retuning the RXs when changing Xtals. They said not to worry. They have piles of RXs in stock. When you order one they just plug in the specified Xtal and ship it out.

The only thing to watch out for is that the RX is compatible with the negative shift TX.

CR

popular belief we do not recommend using another brand of crystal. They are totally different in cut, overtone value and a few other specs. e.g. Hitec DC RX crystals on 35.36 & 40MHz have a frequency 10.7MHz ABOVE the nominal frequency whereas Futaba DC RX crystals are 10.7MHz BELOW nominal frequency. Hitec FM TX xtals are cut at half nominal frequency whereas the Futaba FM TX xtals are cut at 1/3 nominal frequency. Whilst you may get reasonable results in good conditions with Hitec xtals in Futaba RX, Hitec crystals must be used in Hitec RX for optimum results. Futaba single conversion RX crystals may appear to work but with proven less range and glitching, especially noticeable in damp weather or wet ground. Local radio technician was surprised but ran a number of tests with result he is also now convinced that there is a significant difference in the crystals as has also been confirmed by the local crystal manufacturer who supplies USA military and others requirements. For further information, refer to the links provided under crystal compatibility between brands

and sub section "Glitches & Jitter in RX & Servo - causes and cures " in particular "Crystals - Swapping brands in RC Transmitters and Receivers." on my web page. Regards Alan T. Alan's Hobby, Model & RC FAQ Web Links

No problem at all.

Futaba has a Hi and Lo band , 11-36 on the lo and 37 up on Hi band. As long as you stay within that band you're OK.

Ken

On Tue, 2 Oct 2007 23:34:48 -0400, "Chuck" wrote in :

Ah.

OK.

Thanks for the clarification!

Marty

Now someone has to convince me that going from channel 38 to channel 35 in a Futaba Rx is a no-no, but going from channel 60 to channel 39 is OK. It makes no sense at all. Its kind of like Futaba telling us that the diode in the transmitter charge circuit was to guard against line surges.

On Wed, 3 Oct 2007 15:28:24 -0400, "Red Scholefield" wrote in :

I'm not defending the sanity of the recommendation. ;o)

Just trying to remember what it was that folks said about it ...

Marty

Its not a nono, but it may mean a bit less range. You are altereadyu near teh end of teh 'half' band and step over i slightly.

I suspect that actually its more a TX issue. In countriws whee Tx xtals are gaily swapped, you can run into 'out of spec sidebands' going too far.