lm looking at getting a heli radio but what is the difference between a pcm radio and an fm radio

The difference is the format of the data that the RX is capable of decyphering. If the transmitted signal is not in the right format, the RX will not operate the servos/gyro/etc correctly or at all. Obviously, if you have a PCM RX, you must have a TX capable of the same PCM format or it won't work. Likewise with an FM RX, you have to have a TX capable of the same FM format.

If by "heli radio" you mean just the TX then it's not a problem. Most decent TXs can transmit on both PCM and FM and is selectable in the models memory settings. You just have to make sure the settings are correct for the RX in the model. PCM also gives you fail safe options.
Example: Futaba's 9CHP and 9CHF TX's are identical except for the little label on the TX. Both TX models will transmit PCM or FM by setting up the model memory appropriately. So why the difference in labeling? Generally the TX's come as a package and the label indicates the RX type that came with the package. Has nothing to do with the TX (since it is capable of both).

Good Luck,
d.tipton

Nothing they are both FM.

The difference is the way the stick information is encoded and sent to the reciever. As for the price difference pcm recievers are more and thats why the pcm sets cost more, the software is the same. Are they better? Well thats debateable but they do offer you the opportunity to set fail safes in the event you loose signal. This would drive the controls to a preset position until signal is regained or the model hits the ground.

I couldn't have said it better myself.

My personal opinion, I'm not a big fan of PCM. If my heli has a glitch I want to know about it, I don't want PCM to cover it up until it's to late. If your heli goes into failsafe you have no chance of saving it. If you just have a glitch and you see it, you get your heli on the ground and find the problem.
A lot of people like using PCM, I'm just not one of them. I have PCM on my 90 but I have it disabled.

There seems to be a lot of disinformation about PCM. It is not mandatory to have the failsafe. It can be turned off like any other feature in the radio programming. With the failsafe off you can see glitches the same a non PCM. The advantage to PCM is the signal is much less prone to interference. The signal sent from the TX is encoded differently than non PCM. The rx is more selective and rejects more bad signals than a normal signal. PCM stands for pulse code modulation, FM stands for frequency modulation, AM stands for amplitude modulation. The PCM signal is more like a square wave than a non PCM signal and the rx can recognize this signal better while rejecting the enterference.

That's not really true both pulse code modulation and frequencey code modulation are susectible to the same interference, with fail safe off you'll have basically the same amount of interference either way. Then the only difference is that a PCM reciever can cost three times the amount as a normal FM. Not a big deal if you have one helo but if you have multiple recievers the cost adds up.

Well all I know is when I tried connecting my RadioSouth glow starter to the remote, all the servos would jitter (including throttle). With that, I didn't dare start the engine. After emailing RadioSouth a few times, they suggested a PCM receiver. After the switch, the problem went away.

So, I have no idea the difference in PPM and PCM (other than the basics of signal format) but I can say for sure, there was a big difference for me. As far as I'm concerned, there IS a difference between the two and it WAS worth it to change. I do not fly with FailSafe enabled.

Good Luck,
d.tipton

PCM wont cover up a problem such as glitching if a proper pre-flight engine on-off range check is done each time out. You will find a reduction in range during pre-flight in both FM/PCM if there is a problem. Now, the failsafe in PCM operation gives you options on how you want the radio to deal with signal corruption or total loss which are more options than one has with FM. PCM is a more secure data transmission if good, solid safe practices are followed, if not, the FM/PCM arguemant doesn't mean anything anyway. In the end they both will work well if properly set up, some environments however, such as gasoline powered helis, will benefit more from PCM. FM is like the standard seat belt in your car and PCM to me, is more like a 5-point harness in a stock car. Both can save your life but the 5-point harness is better in extreme situations. Mike

evan, it is true, they are different types of radio waves. The pcm while not infallible is much more discerning and will reject more bad signals than the non pcm. I am not trying to start a flame war here but as other people have stated there is a difference. I have had problems that went away with the a pcm set up. I have at least 18 pcm rx in my fleet. I have a few non pcm's in the foamys but other than that they all get pcm. Its a free world and this is just my opinion, no offense meant to anyone.

Look at it this way. PCM is sending a string of numbers. 1s and 0's. If a voltage is there its on and its a 1, if its not there, then its off and its a 0.

PPM is sending a value. Somewhere between all the way off and all the way on. Its easier for a reciever getting a crappy signal to identify if something is off or on, than to discern where between off and on that it is. Hence PCM's better ability to pick out information from an other wise problematic signal.

1024 pcm means that a sticks total travel is divided by 1024 increments, each stick position having an absolute value. 1024 by the way is exactly 10 bits of binary data. 512 was the old version that used 9 bits. The technology allowed them to compress the signal and send more data so now we 1024 resolution, I want to say the 14mz uses 2048 which would be 11 bits of information. The timing of the signal tells the reciever which stick position update (ie elevator then aileron) its getting in a string of numbers.

I see PCM and FM being the differnce between Digital and Analogue signals. If thats true, then yes the PCM will be less prone to interference, correct?

WaynE Kinney , all things being equal, yes, PCM is better but, not always necessary.

I just want to say that PCM is Futaba's brand and QCPM is Hitecs Brand. I happen to have a hitec eclipse 7.

Futaba and Hitec have varing characteristics such as speed of transmission relating to refreshing the signals sent and their stategy for which channels to refresh more or less often.

But I agree with everyone here for the most part.


I have my failsafe set on and my throttle set to 25% or less depending on which model/engine, my goal is to have it drop out of the sky but not to quickly and to turn it into a ball coming at you intead of a bullet. I lift up about 3 feet and turn off my radio and see how fast it falls. Scientific hahaha.

The main thing for me is I don't want a runaway heli hurting someone. My Logo 10 could cut small childern in half. My Shogun could make you cry. and the receiver refreshes very quickly if the signal is recovered, so when they talk about losing it and it doing what you have preset it to do - they are talking about more than a second of lost signal and maybe many seconds - a glich for me that is scary is like losing control for 2 or 3 seconds - It happens, but then it just kinda drifts down and yes can hurt itself but if you have lost control with out PCM or Qpcm with fail safe turned on your gonna have a crash too but maybe at a higher power setting. Once you lose your signal and the hover with power on these heli's take off and excelerate very quickly in which ever direction the wind or something decides or continue where you were heading at high speed.

It really is a weird feeling though, your hovering one second and the next your just sliding down and sidways till you hit the ground. And if you have training gear on you hit and start rolling in some direction and you can't stop it. Slow but not slow enough and then power is back and you stop and say gee, glad the power came back on or I would've run into something.

Sometimes I think I should just set the failsafe to throttle off all the way but that's the point we get to decide with fail safe,.

I hope this helped.
Hitec with spectra about $179 on sale, qcpm receiver $100, regular receiver $15 to $46 maybe. And yes you can select either.

There was some talk about 512 and 1024. I noticed that a ccpm setup (if given a fast collective input) would wave and not travel equally with 512 pcm. It was fine with slower movements. The 1024 pcm fixed the problem.

I found the talk on bits and stick increments to be interesting.

Ihave just changed my receiver in my heli to pcm because I was getting some bad glitches ,more so when flying over a wire fence. I not flown it yet with the pcm one and what fail safe settings should i use or should i just leave them all on norm setting, this is nn Futaba FF9

besides changing your setting on your receiver you need to buya PCM Receiver.

I set mine to about 25% I want to come down but not at blazing speed.

I would try testing it at low throttle levels. and see how hard you fall from a foot hover with training gear on. Think about your Throttle and pitch combo that it takes to get up. and start with a little less. But then you might just want it to shut off. your futaba help line may be able to give you some advice on your heli.

JD