PPM or PCM
04-17-2009 | 08:25 PM
#5
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From: polson, MT
RE: PPM or PCM
epsman,
R127DF is PPM the determining lettering is DF. DP after the number means PCM. Both are FM. PCM is Pulse Code Modulation. Use PPM and if you have RF noise find the problem and fix it. PCM can mask RF to bite you later.
Good Luck,
Darrol
R127DF is PPM the determining lettering is DF. DP after the number means PCM. Both are FM. PCM is Pulse Code Modulation. Use PPM and if you have RF noise find the problem and fix it. PCM can mask RF to bite you later.
Good Luck,
Darrol
04-17-2009 | 08:43 PM
#6
RE: PPM or PCM
I wrote an article partially covering the differences between PCM and PPM a while back. I have copied an excerpt of the article below.
...The transmitter “tells” the receiver where to position the servos many times per second via a particular carrier frequency. The transmission of the individual signals happen so fast that controlling the airplane appears to be perfectly fluid. Depending on the radio system, the number of possible commanded servo positions range from 512-2048.
You’ve probably heard of PPM and PCM. These terms are different modes of encoding. Most receivers installed in trainers use Pulse Positional Modulation (PPM) encoding. PPM is simple and has become the standard method of encoding. The only drawback of PPM is that if, for any reason, interference modifies the signal, the receiver will become confused which will cause erroneous information to be sent to the servos. You would notice this as “glitching.” In response to this shortfall, Pulse Code Modulation (PCM) was developed. With PCM the receiver has the ability to check if the data has been altered. If the data is bad the receiver will discard it and keep the servos at their last commanded position. PCM users can still loose control, but the airplane won’t violently pitch and bank when taking “hits.” Like any other new technology, with the advent of 2.4GHz spread spectrum technology came misunderstanding. Spread spectrum operates on a much higher temporal frequency. The downside to this higher frequency is that any obstruction between the transmitter antenna and receiver antenna will block the signal. This has to do with the changing propagation characteristics between frequency ranges. To overcome this shortfall, spread spectrum receivers are equipped with either two or four antennas. This helps ensure a constant signal flow to the receiver. Be aware, however, that spread spectrum is not immune to interference...
You’ve probably heard of PPM and PCM. These terms are different modes of encoding. Most receivers installed in trainers use Pulse Positional Modulation (PPM) encoding. PPM is simple and has become the standard method of encoding. The only drawback of PPM is that if, for any reason, interference modifies the signal, the receiver will become confused which will cause erroneous information to be sent to the servos. You would notice this as “glitching.” In response to this shortfall, Pulse Code Modulation (PCM) was developed. With PCM the receiver has the ability to check if the data has been altered. If the data is bad the receiver will discard it and keep the servos at their last commanded position. PCM users can still loose control, but the airplane won’t violently pitch and bank when taking “hits.” Like any other new technology, with the advent of 2.4GHz spread spectrum technology came misunderstanding. Spread spectrum operates on a much higher temporal frequency. The downside to this higher frequency is that any obstruction between the transmitter antenna and receiver antenna will block the signal. This has to do with the changing propagation characteristics between frequency ranges. To overcome this shortfall, spread spectrum receivers are equipped with either two or four antennas. This helps ensure a constant signal flow to the receiver. Be aware, however, that spread spectrum is not immune to interference...
04-18-2009 | 08:19 PM
#7
My Feedback: (11)
RE: PPM or PCM
ORIGINAL: [email protected]
epsman,
R127DF is PPM the determining lettering is DF. DP after the number means PCM. Both are FM. PCM is Pulse Code Modulation. Use PPM and if you have RF noise find the problem and fix it. PCM can mask RF to bite you later.
Good Luck,
Darrol
epsman,
R127DF is PPM the determining lettering is DF. DP after the number means PCM. Both are FM. PCM is Pulse Code Modulation. Use PPM and if you have RF noise find the problem and fix it. PCM can mask RF to bite you later.
Good Luck,
Darrol
P is PCM, F is PPM (commonly and mistakenly refered to as FM)
D means Dual Conversion.
PCM has advantages over PPM including fail safe.
04-20-2009 | 08:33 AM
#9
RE: PPM or PCM
ORIGINAL: alfredbmor
Yes a preprogrammed fail safe which can move servos to a certain position to avoid a bigger disaster.
Yes a preprogrammed fail safe which can move servos to a certain position to avoid a bigger disaster.
