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Sep 12, 2015, 01:04 PM
G.F. beurling
G.F. Beurling's Avatar
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Not sure what a seller did with my JR 8103 module. (??)

My question; Is it safe to swap crystals out of a JR 8103 module?

I bought a used 8103 radio in the classifieds 6 months ago. I popped out the channel 56 module that came with the radio, and used my own channel 17 module instead. Fast forward now 6 months later, and I buy a couple of #56 receivers and crystals deciding to use them with the channel 56 module that came with the TX. I now discovered that the JR box says channel 55 on it, and the seller had also advertised it at the time of sale as a channel 55.....not a channel 56. (At the time of purchase I had planned on using my own channel 17 module, so I didn't pay any attention to this to catch it) So..... I don't know if the seller swapped out a complete channel 56 module with complete #55 module, or if he replaced just a #55 crystal with a # 56 crystal. Sure, I will do a field test before flying the plane, but I wanted to know if module crystal swap-out in itself is a bad practice. As far as the seller goes, no animosity toward him as maybe it was a legitimate mistake he made. The radio he sold me looks like new and has worked great using my own modules. I'm just trying to know if this module is safe to use if the crystals were swapped out.
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Sep 13, 2015, 03:39 PM
Registered User
In the U.S. end users can change receiver crystals.

Transmitter crystals can only be change by licensed technicians. If your transmitter uses a replaceable module, you can replace that module, with a module on a different channel, but you can't change the crystal in the module, that must be done by a licensed technician, per FCC regulations.

Changing the crystal, in a transmitter, or module, changes the frequency the transmitter broadcasts on, and that must be checked, and verified. A technician will have the equipment, and be licensed, to do this.
Sep 13, 2015, 04:42 PM
Registered User
In all the rest of the world outside the US it is perfectly normal for users to change crystals in transmitters and/or modules. Even in those places which use exactly the same 72Mhz equipment.

So if someone did earlier make a change from 55 to 56 I'd say it's technically perfectly safe....but it may in theory not be legal in the US.

Sep 13, 2015, 04:48 PM
S.A.D. member
ivanc's Avatar
Most likely, and I repeat it - "most likely" changing the crystal in a transmitter/transmitter module is just fine... BUT... the FCC requires that when done so a licensed tech must check the transmitter/module for proper operation. For that FCC requirement it is not allowed by the end user to change TX crystals in the US.
Sep 13, 2015, 06:20 PM
G.F. beurling
G.F. Beurling's Avatar
Thread OP
Guys...... I was already quite aware of the FCC having rules that regulate this........
......but my concern and reason for posting this was less about legalities and breaking FCC rules, and more about breaking my plane ....... which can happen in the event of signal loss.

As explained in my opening post, I'm not sure what the seller did. But, from what I gather, it will likely work anyway even if the seller jacked around swapping out the crystals. I'll be sure to do a thourough range/ ground test. Thanks for the help.
Sep 13, 2015, 07:54 PM
most exalted one
And I believe especially OK if it is 55 and 56. There was a tuning for low and high with some. Obviously these frequencies are so close they should be OK. Inexpensive test platforms are always best.

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