I was browsing the for sale ads on here earlier and have a few questions.

Regarding matching the transmitter with the receiver. If a person buys just the transmitter, and then later finds a receiver on the same channel, is it absolutely necessary to send the tx and rx in to a place like Horizon and have it tuned?

If so, can a local electronics repair place do this sort of work?

Can you use a different brand reciever and transmitter ie: a Futaba tx and a JR receiver both on channel 26? Or is it proprietary stuff and only matched brands will work?

There are a lot of different transmitter / receivers available from any Manufacturer.

In the case of JR some transmitters won't transmit in the PCM mode (basic radios) so not all transmitters / receivers will work together. I would suggest sending the items in for a check up in any case (I use JR service center as they have the parts needed just in case).

Member dsnyder here at RC Universe in the following fourm is the best contact for JR information.
> Radio Manufacturer Support Sub-Forum > JR Radios - Ask Danny at JR

http://www.rcuniverse.com/forumdispl...s=&forumid=174

EXCAP232

ok first you need to know that there are two "shifts" of signals out there. negative and positive

hitech and futaba are negative, jr and airtronics are positive. you cant mix shifts, so if you have a futaba TX you cant use a jr RX.

now there is PCM (pulse code modulation). this is a way of encoding the signal into digital format to help filter out interference. a non PCM transmitter cannot work a PCM reciver. although most PCM transmitters can go into normal FM mode (or PPM as its called)

to further complicate things hitech and other brands offer receivers in both positive and negative models so its available to anyone.
and hitech makes a transmitter that can change its shift to work with any (non PCM) reciever


now for as for matching channels you can change the frequency of the reciever by swaping crystals out, so if you have a RX thats originally on channel 30 you can buy a channel 35 crystal and use that.

FCC regulations state that you cant change the crystal in the trasmitter unless you are quilified and licenced to retune the radio section. the manufacturers got around this with TX modules that have the entire "tuneable" section in this module, so you can swap it out and change frequency.


sorry if this has confused you but it is better to do some research now then end up frustrated hours at a time later (or worse have something go "wrong")

if you use futaba brand radios (or are considering them) you can post in the radio section under manufacturers direct support/futaba ask A.M.Cross of great planes to Ann Marie Cross (user ID amcross), She is an excellent source of information and support, and has been VERY helpful with some issues that I and others have had.

also she would recommend reading the FAQ on the futaba website http://www.futabarc.com/faq

good luck and happy flying

Thanks for the info guys. It helped.

actually the hitec eclipse is negative and positive shift

Unsatble's explaination sounds good.

I would like to add one thing. Crystals are peices of quartz. A peice of quartz will vibrate at a given frequency. Not all peices of quartz are identical. It is best to have the TX and RX crystals made from the same peice of quartz. They are generally considered paired. I said it is"best"if they come from the same quartz. However, you will see people flying with an unmatched set of crystals.

Actually that is a misconception. It would not make any sense to have Tx and Rx cystals "made from the same piece of quartz". Due to the way radios work Tx crystals and Rx crystals are very carefully made to resonate at DIFFERENT frequencies.

It is however a good idea to get your Tx and Rx crystals from the radio manufacturer so they are matched, i.e. made to the correct specification.

To answer the original question, if you buy a transmitter you can later buy a suitable receiver, but be aware that not all makes work together. The receiver does not have to be on the same channel as you can simply change the receiver crystal to match the transmitter (for any make other than Futaba). The rules for Futaba are a bit more complex. But you will not normally need to have anything retuned unless you want to change the *transmitter* channel.

Steve

I found additional info on the subject at other posts on RCU. I

will put it here as a follow up.

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

The way I understand it is that the TRANSMITTER's frequency

module electronics need to be tuned to it's crystal. It's OK to

swap out entire modules but not OK to change individual

crystals.

RECEIVERS however do not need to be so finely tuned; therefore

you are allowed to change crystals.

I believe the reasoning is that out of tune transmitters can

interfere with other channels and other planes but an out of

tune receiver won't cause interference because it doesn't SEND

out any signals.

The exception being you can't mix a PCM receiver with a non-PCM

transmitter. Some transmitters however, can be either PCM or

plain FM (non-PCM) so those may be used with both types of

receivers.
--------------------------

You're misunderstanding matching. Matching is when someone

sends us their transmitter and receiver both. We tune the

transmitter to its maximum output, adn then tune the receiver

to the best possible reception of this transmitter. This is

done only rarely and is usually done for high $$ specialized

aircraft htat are having noise interference problems.

you can change your receiver channel at any time by changing

crystal as long as you stay int he right half of the band

(11-35 or 36-60); you are not supposed to change your

transmitter crystal at all except to replace one which got

damaged, for example, when dropping a transmitter.