Thread: FM or PCM??
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Old 02-11-2004, 03:51 PM
Join Date: Mar 2003
Location: Tokoroa, , NEW ZEALAND
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Default RE: FM or PCM??

> In the begining every PPM system came with a failsafe system.
> It was deemed to be unnessesary and dropped. In fact one of
> the manufactors, PCS, told me that it caused more crashes than
> it saved

"In the beginning"?

When digital proportional gear first began appearing on the scene, I was involved in the design of several systems and also serviced quite a bit of commercially made RC gear.

I don't recall *ever* seeing a PPM system that had any kind of fail-safe system.

Back in those days, all the encoding/decoding was done with discrete transistors and there was no such thing as "memory" -- so how would such a failsafe system have worked?

To the best of my knowledge, there was no "failsafe" assocaited with PPM until the advent of microprocessor-based decoders -- which only appeared 20 year so after the advent of PPM.

I expect the reality is that the PPM/PCM debate will continue virtually for ever -- just as there are still audiophiles who swear that valves and vinyl are superior to today's latest digital audio discs and solid-state amps -- and who knows, in some cases they may be right.

The reality is that the quality of today's radio gear is very high and 99.9% of the time, people won't notice the difference between PPM and PCM in everyday flying.

I expect that the only time we'll get rid of this argument is once we've all switched to spread-spectrum equipment that should, for all intents and purposes, significantly reduce the problem of interference from external sources. By that time, all systems will be PCM (or a more advanced variant thereof) anyway.