rogue313392002

I just purchased a JR XP662 used and I was wondering if I would have to send the Tx in to get the channel changed or can I just change it my self?

Carpilot

Yes, you should send it in for the channel change and re-tune, FCC regulations prohibit schanging crystals in 72MHZ fm transmitters.

BarracudaHockey

My Feedback: (11)

That is correct. Aside from JR you can contact Radio South http://www.radiosouthrc.com

Skarn

I've seen some debate about that. The FCC reg states something to the effect of changing the frequency not the channel. So there are a lot of folk that agree that as long as you stay in the 72mhz range, you can change the channel. I tend to agree, why else would they sell the crystal's freely at your LHS without any issue? I'ts a simple $10 change.

Skarn

Carpilot

A channel is a frequency, for example channel 44 has a frequency of 72.670 MHZ. which is different than channel 21, which has a frequency of 72.210MHZ. If you change to another channel you are changing the frequency!

And yes I have seen people swap transmitter crystals without regard to the FCC rules but I'm not risking any of my models like that. besides I am a licensed radio amatuer for 20 years and I know a thing or two about TX.

If you really need to operate on different channels all the time I would reccomend getting a systhesized radio, XP7202 or comparable, it will operate on any channel and you don't have to change any crystals. or spread spectrum no worry about channels there either.


This is how it works, the board that the crystal plugs into in the back of the radio has some adjustable RF coils on it, those are adjusted to get the proper RF output levels on that frequency, when the frequency (channel) is changed, the RF power level will drop. the farther away from the "tuned" frequecy you get the more it will drop. That is why FCC regs. say that it needs to be done by an authorized technician.

the technician will change the crystal and adjust it for the proper RF output levels and bandwidth. these are narrow band TX's

Also if you look at the frequency list in the back of your manual you will see how close the channels are to each other, it's in everyones best interest to use a properly tuned TX!


Some time ago at the field there was a flyer who was on the same channel as me, he swapped out his TX and RX crystal and moved 1 channel away, I still didn't fly until that transmitter was in a case. transmitters that are not tuned properly, will not have the proper bandwidth and RF power. and I'm not flying my model while there is an out of tune narrow band TX just 1 channel away.

bruce88123

There is NO legitimate debate. It IS flat out illegal. Please read this comment from one of the manufacturers reps who goes into detail on the subject.

http://www.rcuniverse.com/forum/fb.asp?m=4804374

BAX is the Futaba rep in the US. I've seen similar comments from Danny who is the JR rep.

Skarn

Thanks all for the enlightenment! I did know that changing a channel is actually changing the frequency, but I didn't realize it was illegal! I guess a lot of the guys at RC clubs don't realize it either!

Skarn

BarracudaHockey

My Feedback: (11)

Its a 10 grand fine per occurance if you cause a problem, if you got that kind of cash go for it.

pilotpete2

So true, and "Ignorance of the law is no defence"
Not a Lawyer, and didn't sleep at a Holiday Inn Express
Pete

Eplane65

My Feedback: (16)

OK, then why am I able to change my JR 9303 from a fixed frequency module to a synthesized module and change frequencies to anything I want? If what you guys say is true (technically, it probably is by law) then JR is breaking the law by selling individual TX crystals. You can't buy TX crystals from Airtronics.

I tend to think this is a bunch of government gobbldygook.

MikeL

My Feedback: (3)

Because that's exactly the sort of flexibility that a synthesizer is intended, designed, and certified for. Why else would people use them?!

You're entitled to your opinion, but does your opinion change the law or the nature of the electronics? If you choose to save yourself a couple of bucks, I hope you have the moral courage to stand up when/if your savings costs someone a model (or more!). We have a responsibility to each other and to the hobby as a whole to make sure that our equipment is maintained properly.

Mac_Man_UK

I do believe that the regulations state that you cannot change a frequency determining component. A crystal is a freq. determing component, however a synth unit has a FIXED reference inside and all you are adjusting is a variable division ratio. This is NOT a freq. determing component and hence you are allowed to change it.

I would imagine that the crystals being sold across there are for a 1 for 1 replacement ie if you are using a channel 63 Tx Xtal, then you can legally replace it with a channel 63 Tx Xtal ( Crystals do age and can go faulty)

bruce88123

You can swap a crystal controlled module for a synthesized module because ALL of the critical tuning circuits are within the module. If you were to change the crystal within the crystal module it (the module) would then need to be sent for tuning at a shop.

No you can not remove a Ch 63 crystal and replace with another Ch 63 crystal. No 2 crystals are identical. These are basically just chunks of precision cut rock and there is only just so much one can do to guarantee accuracy. There is still a tolerance that must be tuned for.

The crystal are sold because the radios are sold worldwide where the same laws may not apply and also so that you may purchase the part and take it to you radio shop if you desire a change.

Please do yourself and others a favor and stop trying to find a way to avoid the laws and just follow them. (Not directed at any particular person)

Carpilot

Synthesized modules have no crystals, thus, no need to tune for variance in crystals. JR is not breaking the law by selling TX crystals and is just ridiculous to state they are. It's what the end user does with that crystal that makes it legal or illegal, just like any other product.

government gobbldygook, maybe but...
There are commercial users between the frequencies that we use who pay big money for a licence to operate, go ahead and interfere with one of those with a improperly tuned TX and see what happens.

bruce88123

To carry this analogy one step further:
Gun dealers sell guns. They don't know if you are buying it to protect yourself or to rob a bank or commit murder. Don't blame the dealer - blame the end user.

Please - no comments from anti-gun nuts. I don't want to hear it.