RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

Someone please give me a clue!

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Old 02-21-2003, 10:20 AM
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deltamech
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Okay, I just got a Futaba FP-7UAPS, FP-7UAFS. Now I actually consulted the manual but still don't know what this PPM mode, PCM mode stuff is all about. What is this and what the heck is the difference, should I care?
Also, what is this "dual conversion" reciever all about? Thanks for any help,
Steve
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Old 02-21-2003, 10:54 AM
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BALSABRO
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PPM and PCM are the two types of modulation that your transmitter is capable of transmitting. PPM is really just FM and PCM is further defined modulation and has much less interfencance from outside sources it is better of the two. however you must have a PCm receiver for this to work. Most units are PPM(FM) not something to really worry about. Dual conversion has to do with the signal shift positive or negative shift dual conversion means that it will work with either shift (servos) howver the tx and rx crstal must be dual conversion xtals.
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Old 02-21-2003, 12:08 PM
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HarryC
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Ahem! Letís put a few things straight again.

Your radio is FM, end of story. PPM and PCM have nothing to do with the FM radio. PPM and PCM are ways of encoding the data, PPM is analogue and PCM is digital. PCM is slightly better at dealing with interference. You will need a matching PCM receiver from the same brand as the Tx, PCM Rx are more expensive. PCM allows failsafe programming. For most people, PPM is fine.

Dual conversion has nothing to do with selecting the frequency shift, and servos do not recognise any difference in shift. Dual conversion is purely a receiver process that blocks image frequencies from Tx that are 2*IF away from your frequency from causing problems, and it also blocks similar problems from frequencies that are multiples of yours. DC receivers are more expensive than single conversion and needs the DC crystal, your sc crystal won't work in it. Most people find that single works fine but DC might be preferable in the radio environment where you operate. The Tx most definitely does not need a DC crystal because it has no idea whether the Rx is SC or DC.

Frequency shift is a problem made by Futaba purely for the North American market, so that other receivers will not be compatible with Futaba Tx, and other Tx not compatible with Futaba Rx. It is a marketing con to lock you into Futaba products. The data coming out of the Rx is always the same though, so any brand servo can be used with Futaba and likewise Futaba servos can be used with any brand Tx and Rx.

Harry
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