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HelicopterBeginners Corner › FM vs PCM
09-02-2003 06:12 PM  14 years agoPost 1
gaanel

rrApprentice

Greenville, SC

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I am in the market for a new Heli radio.
Why is the PCM considered better than the FM?
Less glitches?
I fly FM now and don't seem to have any problems. I don't know if spending the extra money is worth it.

Thanks,
Gary

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09-02-2003 07:10 PM  14 years agoPost 2
gaanel

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Greenville, SC

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Search

Yes, I usually do search. However, the problem is what to put in. Putting in PCM brings up a bunch of info you have to weed through. Plus, there may be different opinions from different members on line now.

From what I know now, I think I will by the Futaba 9CH transmitter. It should work with my FM receiver I have now. When I can afford it I will by the PCM receiver.

Gary

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09-02-2003 08:07 PM  14 years agoPost 3
BROWNIE92

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Joplin, MO

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Your FM receiver should work fine (as long as the Freq match) you will just have to put your tx into FM mode.

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09-02-2003 08:55 PM  14 years agoPost 4
gaanel

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Greenville, SC

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Tom Fiddler

Yes, I plan on going to the Black Sheep Fun Fly. Probably only be able to go on Saturday. I am looking forward to it though.
Maybe I will see you there.
Gary

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09-02-2003 11:10 PM  14 years agoPost 5
inventory

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CA

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I fly a 148 fm rx with my 9ch and have no problems, never had a glitch yet (about 3 months in). The only reason I can see for using PCM is for a gy601 or on a gasser.

There are at least a thousand people who will disagree with me......

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09-02-2003 11:25 PM  14 years agoPost 6
GregKRC

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Auburn, AL

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The Failsafe feature would be a nice safety item.

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09-02-2003 11:36 PM  14 years agoPost 7
inventory

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CA

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Thats true, I normally fly out in the boons, we have lots of open spaces out here, so I'm not to worried about the unlikely catastrophic complete lockout (i.e., the bird just flies away); it would crash long before it could hit anything; so I'd rather have a chance at fighting the glitching and bringing it down.

If I flew in a more populous urban environment I probably would get PCM as a way of reducing any possible legal liability.......

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09-03-2003 02:57 PM  14 years agoPost 8
Wright Flyer

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Finchingfield, England (UK)

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Haven't you got the original question a little confused? Don't you mean which is better PPM or PCM? Both of them are type of signal transmitted on an FM carrier. (So PCM is just one way of using FM)

Cliff

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09-03-2003 04:43 PM  14 years agoPost 9
gaanel

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Greenville, SC

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PCM vs FM

I suppose what I am really asking, is should I spend the extra bucks to get the PCM receiver, or just buy the transmitter and use it with my current FM receiver (which does not have PCM capability). Does anyone really have bad glitching with the FM receivers? I fly my standard FM system now and have not noticed any glitches.
At this point in my heli career, the most I can afford is the transmitter. Maybe I will upgrade the receiver later.
Gary

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09-04-2003 01:18 AM  14 years agoPost 10
captain1

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Sydney - Australia

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"Both of them are type of signal transmitted on an FM carrier. "

Sorry but I had to reply to this statement. Yes PCM is a signal transmitted on an FM carrier, but then so is a lot of digital modualtion techniques used today. This does not make it in any way similar to PPM. PPM is essentially an analogue transmission with little or no error correction. The pulse width of the signal directs the servos where to go. If the signal is distorted the servos go to the distorted location as if the transmitter sent them there.

PCM on the other hand is a digital signal. As such the commands are represented as a binary sequence of ones and zeros. The biggest advantage of this is that now that there are microporcessors on either side manipulating and processing the data error detection can be imposed. In the case of PCM a CRC (checksum) is added to the data. Thus is the CRC fails on teh receiver side due to distortion of the signal the receiver essentially ignores that command and waits for the next one.

Here's an interesting webpage on PCM for those who are interested:
http://www.aerodesign.de/peter/2000...CM_PPM_eng.html

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09-04-2003 05:41 AM  14 years agoPost 11
Rick_H

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Boulder City, Nevada

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If you don't want to upgrade your TX take a look at FMADirects new FM Receiver FS5I (P.C. Ready) Part Number: FS5I. It works with any FM TX and provides the protection you are looking for. At least that is what they say. I don't know anyone who has one yet, but I have been considering getting one to play with.

Rick

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10-10-2004 05:40 PM  13 years agoPost 12
andyR50

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Glasgow

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148 FM PPM rx glitch

Hi,
I am experiencing problems at the moment with a PPM 148 rx on my Raptor 50 V2. There is an intermittent glitch that affects the pitch. The heli jumps about 2 feet in the air. I have replaced the pitch servo and disconnected the Governor but still not fixed. I have a 9CHP Tx so I will be buying a PCM receiver to see if the 148 is at fault.

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10-10-2004 11:39 PM  13 years agoPost 13
GBNT

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uk

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Sorry
wrong post

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11-06-2004 12:12 PM  13 years agoPost 14
Rappy da Raptor

rrVeteran

Dorset

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Someone at my club had problems with servos glitching and he had a FM reciver he was waisting so much time trying to solve the problem so he decided to splash the cash and get a PCM reciver it solved all the problems

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11-06-2004 12:19 PM  13 years agoPost 15
GBNT

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uk

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Are they solved?
Or are they hidden/masked?

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11-06-2004 02:30 PM  13 years agoPost 16
greenboot

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Marblehead, OH

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Gary,
Don't be confused by all the talk of how electrons flow along the transmission wave. Those guys are just showing off.

If your FM receiver is working for you, then just keep using it. And yes, you can purchase a PCM receiver when you get the money or decide you need one. The 9C transmitter is the same for both and it can transmit to either type of receiver.

Cliff,
When you hear the term FM reciever in the context of RC transmitters, we are talking about PPM. That's just the way we use the term cause it's much easier to differentiate PCM/FM than PCM/PPM. You probably do enjoy getting the technical jargon correct, but it is easier for us to use the more slang terms. BTW, if I ask for a Kleenex, I really mean facial tissue.

GBNT,
A PCM receiver does not improve the quality of a radio transmission as you know. But it does a fabulous job of removing (hiding) those twitches that practically give me a heart attack. That's one of the features I like the best. I do wish the manufacturers would add an LED to indicate how many glitches were removed so I could monitor the signal quality.

Tom

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11-08-2004 04:44 AM  13 years agoPost 17
Comanche Man

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U.S.A.

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pcm

Fear my name on Xbox live

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11-08-2004 10:31 PM  13 years agoPost 18
rob10000

rrKey Veteran

Western Massachusettes

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FM only for me.
I would rater see the glitches, and find a way to solve them.
PCM will mask them. You may not even know you have a problem that is getting worse untill your reciever goes into failsafe mode.

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11-08-2004 10:47 PM  13 years agoPost 19
earl

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Belfast, Northern Ireland

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Hi Guys,
Have been readiing the posts so far. Seems to me there are pro's and con's for each system.

If you are worried about glitches being masked, you can buy a Glitch counter to install on the model. It is supplied by Mainlink systems, and is compatible with both PPM and PCM.

Check it out at:

http://www.mainlinksystems.co.uk

Trevor

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11-09-2004 10:01 PM  13 years agoPost 20
Rappy da Raptor

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Dorset

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Hi GBNT,

Yes they were solved

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HelicopterBeginners Corner › FM vs PCM
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