What is the difference FM and PCM?

[byhsu]

Hi Everyone:

Does it matter if the receiver that comes with the radio is PCM and not FM?

I need a crystal for the receiver and one for the transmitter?

Thank You

[Aztek1701]

Hi.

PCM stands for Pulse Code Modulation and its a way of encoding the signal sent to the aircraft in such a way as to me less suseptable to interferance. PPM stands for Pulse Position Modulation and is more prone to getting interfered with. They both use the FM wavelength.

You will need a crystal for the transmitter and one on the same frequency for reciever. This is your channel number, also you need to pick the right crystal for the Reciever, ie, a Dual conversion crystal wont work in a single conversion rx. You dont need to worry about this tho cos the shop should give you the right crystal.

Take a look here for more info...

http://www.aerodesign.de/peter/2000/...ml#Anker144123

Take care... Azzy

[byhsu]

Azzy:

Does dual conversion mean the receiver can receive FM(PPM) and PCM signals?

Thanks

[Aztek1701]

Hiya,

Nope, the PCM / PPM bit is done in the reciever, not the crystal. As I understand it, dual conversion is a way of "cleaning" the incomming signal to reduce interferance

Take care... Azzy

[byhsu]

Originally Posted by Aztek1701

Hiya,

Nope, the PCM / PPM bit is done in the reciever, not the crystal. As I understand it, dual conversion is a way of "cleaning" the incomming signal to reduce interferance

Take care... Azzy

Azzy:

So if I had a radio that is PCM then the receiver will have to be PCM too then? Can't use an FM receiver with a PCM transmitter, correct?

Now, I wonder if the Hitec Electron 6 is a PCM or just FM receiver?

I was going to buy a Futaba PCM transmitter and receiver, but was afraid that if I got another Heli, to share the transmitter, I would have to buy a PCM receiver, and so far I haven't found many that are small like the Hitec. The futaba receiver is more expensive too, if you just buy it without the radio combo.

Do you use PCM or FM transmitter?

[Aztek1701]

A lot of Txs can do both PCM AND PPM (my FF7 can for sure and I know that the JR radios can too), Given the price, the electron 6 is most likely PPM because PCM rxs are typically about 1.5 - 2 times more expensive. If it doesnt say its PCM its probably not.

My FF7 is running 2 helis on PPM (FM as you wrote) a T-Rex and a small Sceadu and 1 heli on PCM, my big Sceadu.

So your answer is.. Check if your TX can do PCM and PPM, I know the FF7 can but Im not sure if the 6 channel ones can.

Take care... Azzy

[byhsu]

Thanks very much for the clarification, that is why I went with the PPM(FM) model. The Futaba 6EXH TX that I bought has either PCM or FM, but not both of them together. I chose FM just because the receiver for PCM were more expensive if you were to buy them alone.

[uneverno]

Hey byhsu,
PPM and PCM can't be run together. It's an either or thing, with, as Azzy said, many PCM TX's capable of transmitting PPM as well. If where you fly is free of interference, PPM is fine. PCM gives you some extra protection in areas of high radio traffic, power lines and things of that sort. (and, yes, power lines will glitch an FM radio - even though in theory they shouldn't)
Rule of thumb I typically follow is if it's on the ground, eventually it'll hit something and stop without hurting too much more than the vehicle, so PPM and lower $$'s fine. In the air I want as secure a signal as I can get.