I just discovered how tricky it can be to buy rc stuff on ebay.
This is because there arfe a lot of parameters to consider, some of which you may not realise.
Here's what I now know, hope it saves you making as many mistakes as I did. I'll start with what you should all know, and then add the less obvious stuff.
1. There are many different radio frequency bands eg: 27, 35, 40, 72, Mhz and 2.4 GHz are the common ones. A transmitter adn reciver always need to be in teh same band.
2. inside those bands there are many different channels, most often selected by fitting a CRYSTAL into the Transmitter and the Reciever. HOWEVER one cystal that works on (say) channel 26 in one transmitter may well cause a different make of transmitter to work on teh wrong channnel (if at all) PLUS receivers come in single and dual conversion versions, each type of receiver, tends to like it's own special crystals.
3. having got your transmitter and receiver working in teh same band and on teh sdame channel, then there is the modulation to consider. Modulation is a process where your ctick positions are encoded into the radio wave, and there is at least three ways of doing that currently in use. AM (Old fashioned, and on the way out, now. ONly small toys and really old stuff uses AM) FM this comes in two flavours positive and negative, and futaba do it one way, and JR do it the other way, making it impossible (without re engineering your particular transmitter) to use a JR receiver With a FUTABa transmitter and vice verca.
4. type of control pulses, these come in two main types PPM and PCM and the two don't mix, so your newish futaba PCM receiver almsot certainly won't work woth your old futaba ppm transmitter. A few of the latest type of recivers do both ppm and pcm... Most do not!
5, Finally helicopters have their own sort of transmitter, it's called ccpm, and that is another whole layer of complexity.
SO to sum up, if like me you want to make the ultimate custom rc set at a low price and you buy a seven channel 35 Mhz futaba transmitter for 30 quid expecting it to work more than one of your models, forget it, unless you are prepared and able to change most of the recievers to suit.
In this case expensive is deinitely better. the really expensive transmitters do both PPM and PCM, have exchangeale modules in the back so as you can change BAND as well as Channels, and the really expensive receivers use pcm can work with eitehr JR or futaba and do not require crystals.
Complicated isn't it?