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Frequency question

Old 10-27-2007, 05:12 PM
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Tcat1000
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Default Frequency question

Hi Boys & Girls...............Just a quick question concerning changing crystals..................Can I change my lets say frequency 40 to 39 or 41...........or my ch 19 to 18 or 20? I only want to change one ch either way because of conflicts. Or do I have to send in my TX & RX to get this done? (FUTABA)

Thanks in advance...............

Tcat
Old 10-27-2007, 05:25 PM
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TLH101
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Default RE: Frequency question

You can change the crystals in recievers to match transmitters, but you cannot (legally) change the "crystals" in transmitters. It must be done by a certfied tech. You can however, change the transmitter frequency, if it has a plug-in module.
This is from a sticky on RCG:


"FAQ - Transmitter crystal swapping (USA)

--------------------------------------------------------------------------------

There's always a lot of discussion on this subject. In an attempt to avoid at least some of the repitition here are the relevant parts of the FCC regulations which forbid users from changing crystals in the R/C transmitters. If you wish you can look up the detail for yourselves from http://www.access.gpo.gov/nara/cfr/...47cfr95_00.html or by doing a search on "FCC Part 95".

I have emphasised certain sections by making them bold.

Sec. 95.222 (R/C Rule 22) May I make any changes to my R/C station transmitter?

(a) You must not make or have anyone else make an internal
modification to your R/C transmitter.
(b) Internal modification does not include:
(1) Repair or servicing of an R/C station transmitter (see R/C Rule 21, Sec. 95.221); or
(2) Changing plug-in modules which were certificated as part of your R/C transmitter.
(c) You must not operate an R/C transmitter which has been modified by anyone in any way, including modification to operate on unauthorized frequencies or with illegal power. (See R/C Rules 9 and 10, Secs. 95.209 and 95.210.)


Sec. 95.645 Control accessibility.

(a) No control, switch or other type of adjustment which, when
manipulated, can result in a violation of the rules shall be accessible from the transmitter operating panel or from exterior of the transmitter enclosure.
(b) An R/C transmitter which incorporates plug-in frequency
determining modules which are changed by the user must be type accepted with the modules. Each module must contain all of the frequency determining circuitry including the oscillator. Plug-in crystals are not considered modules and must not be accessible to the user.


Sec. 95.653 Instructions and warnings.

(a) A user's instruction manual must be supplied with each
transmitter marketed, and one copy (a draft or preliminary copy is
acceptable provided a final copy is provided when completed) must be forwarded to the FCC with each request for type acceptance.
(b) The instruction manual must contain all information necessary for the proper installation and operation of the transmitter including:
(1) Instructions concerning all controls, adjustments and switches that may be operated or adjusted without resulting in a violation of the rules.
(2) Warnings concerning any adjustment that could result in a
violation of the rules or that is recommended to be performed by or under the immediate supervision and responsibility of a person certified as technically qualified to perform transmitter maintenance and repair duties in the private land mobile services and fixed services by an organization or committee representative of users of those services.
(3) Warnings concerning the replacement of any transmitter component (crystal, semiconductor, etc.) that could result in a violation of the rules.
...

SL COMMENT:
It seems obvious to me that the intention that "plug-in crystals" shall not be user accessible and that changing them shall count as "internal modifications" and not be allowed. It is also clear that Hitec synthesiser modules should not be used with Futaba transmitters as they were not "type accepted with the modules".


NOTE : all of this applies only to the US. Most other areas of the world permit crystal changing without restriction, even on exactly the same equipment used in the US."
Old 10-27-2007, 09:34 PM
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Bad_Daddy
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Default RE: Frequency question

Reality - If you can buy a TX crystal in the same "Lower" (11-35) or "Upper" (35-60) range, just swap it out and go. I've never had any glitch or reduction of range with my Futabas.
Old 10-27-2007, 09:54 PM
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Default RE: Frequency question

Thanks guys for the replies.............I kind of remembered that it was a TX issue but couldn't remember for sure. I sure wouldn't want to do any thing illegal like changing a TX crystal, speeding, stealing, wife swapping, Hmmm.............don't think the latter is illegal though.......or is it...................Oh forget it.................

Thanks again

Tcat
Old 10-27-2007, 11:12 PM
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Default RE: Frequency question

In fact, legally you can not even take out one channel 40 crystal and replace it with a different channel 40 crystal. The FCC simply says: "Keep your cotton pickin' hands off the darn thing!"
Old 10-28-2007, 07:57 AM
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Default RE: Frequency question

Just because things seem to work when you swap out crystals does not mean you are not causing someone else a problem. There are no two crystals exactly alike, even from the same manufacturer and production line. That is why you need to have someone with adequate instrumentation and knowledge check it out when you change crystal. This is to keep you from inadvertently causing someone else a problem (not necessarily a fellow RCer--could be a construction crane etc.). Yes many people do it and get by but is it worth the risk to someone else? I look at people who do this just as I look at those who speed through school zones etc. because they think they are good enough to avoid the inevitable.
Old 10-28-2007, 08:06 AM
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Default RE: Frequency question

There seems to be a bit of confusion about crystal swapping in tx's....

A lot of guys figure the only reason not to do it is because the FCC says no, I'll give you the reason why.

Just because it's a crystal, doesn't mean it will be "on frequency" and a new crystal installed on a radio capable of transmitting radio frequencies must be checked for that and fine tuned as necessary. Also, the max/min power output will be verified.

So basically it's there to make sure you don't mess up someone else's stuff. If you don't mind running the risk of losing your own models that's one thing, but messing up someone else who might be affected by your slightly off frequency tx is another matter.

This is the reason you now have frequency module equipted tx's, so you can change the frequency yourself as all the RF components are inside that module and tuned.

edit info:

Looks like Rodney beat me to it....
Old 10-28-2007, 08:21 AM
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Default RE: Frequency question


ORIGINAL: Bad_Daddy

Reality - If you can buy a TX crystal in the same "Lower" (11-35) or "Upper" (35-60) range, just swap it out and go. I've never had any glitch or reduction of range with my Futabas.
but you do risk bleed over and shooting someone else down
Old 10-28-2007, 10:42 AM
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Default RE: Frequency question


ORIGINAL: Bad_Daddy

Reality - If you can buy a TX crystal in the same "Lower" (11-35) or "Upper" (35-60) range, just swap it out and go. I've never had any glitch or reduction of range with my Futabas.
"lower" and "upper" have nothing whatsoever to do with transmitters. Transmitters are tuned to the frequency which they transmit on, its illegal (in the US), and irresponsible, to mess with crystal based transmitters without the equipment and knowlege to tune them.

The black suburbans probably won't pull up in front of your house if you shoot another model down but if you cause a problem for the commercial users between our channels (read that as high paying commercial users) then I can promise you that the FCC will take action. Its a 10K fine PER OCCURANCE.

Oh ya, and if you did cause an injury accident that resulted in an investigation, and it turned up that you illegally modified your transmitter, your insurance company would be sending you a thank you card for letting them off the hook.

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