ORIGINAL: modeltronics
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I am also an engineer and can tell you that to say a PCM receiver is better is wrong. If you look at 2 double conversion receivers of the same design one being standart FM and the other PCM decoding they will both have the same sensitivity and selectivity. The decoder section that is in the same case as the receiver is very different but both receivers are the same. If you look at the descriminator of both receivers when at the end of a range check you will see the same thing, degridation of signal. But the decoder section that is fed from the receiver to the output can mask many problems on a PCM receiver.
Yes the front end of the receiver is the same. However in the late 50's when the RADAR's of the day went to inter pulse coding the signal to noise ratios increased by about 3 db. This is because the decoder was able to read and recognize code further down in the noise than random inputs. A 3db increase in s/n ratio is the same as doubling the transmitter power. Also each pulse data contains its own identification and does not depend on integrety of the frame as PPM does. Since the frame is not synchronized with the engine ignition an ignition interference pulse is not likely to occur in the same pulse twice. The PCM decoder recognizes the bad pulse and throws it out. Some say that the PCM receiver just covers up interference. Yes that is what it does. That is what it was designed to do. With that comes a extra measure of protection. I just set the fail safe to shut the engine off. If I get ignition interference that overwhelms the PCM receiver it shuts the engine off and I get the control back.
I find that my PCM receivers give me about twice the range of my PPM receivers. Are you interested in some used PPM receivers? I'll make you a deal. PM me.