How to get a PPM signal from old Futaba PCM radio? - RC Groups
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Aug 21, 2011, 06:54 AM
Steamers & Military Ships

How to get a PPM signal from old Futaba PCM radio?

I am helping out a friend. He has an old Futaba FP-T8H-P radio (non computer) which we woud like to convert to 2.4 GHz with a FrSky DIY module. The radio seems to be an earlier verson of this one: The FrSky module requires a PPM signal but this a PCM radio. There is no trainer connection, just a connection for a charger (only two wires on the inside), and I have not found any switches to change from PCM to PPM.

Does anyone know if it is possible to get at PPM signal out of this radio?

Last edited by HelgeBe; Aug 21, 2011 at 03:19 PM.
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Aug 21, 2011, 09:59 AM
Dave the Rave
dmccormick001's Avatar
I could be wrong (if I am I'm sure somebody will correct me), but I think the type of signal being transmitted (PPM vs PCM) is determined by the circuitry in that RF module. If you replace it with something different, like a 2.4GHz PPM module, everything should work OK.

I've personally never seen a Futaba like that. Interesting collection of features.
Aug 21, 2011, 11:16 AM
Registered User
coriolan's Avatar
The RF section has nothing to do with the encoder output (ppm/pcm), it just set the modulation type (AM/FM) and frequency band from 27 Mhz to 2.4 Ghz. The Tx in question has a DSC output combined with the charging jack (DIN-6)but that signal is most likely a digital number serie (PCM) instead of a pulse train with variable length like PPM. The best way would be to check that signal with a oscilloscope to determine if it is ppm or pcm. If it is PCM only you won't be able to convert that Tx.
Aug 21, 2011, 11:33 AM
Registered User
Try to check the signals that go into the RF module. You will need an oscilloscope or a logic analyzer for that. I'm pretty sure that you will find only a PCM signal but that is your best chance.

Just seen coriolan's answer. I agree.
Last edited by itai n; Aug 21, 2011 at 11:39 AM.
Aug 21, 2011, 11:50 AM
Oxford Panic
AndyOne's Avatar
The slightly later FF7 transmitter had the facility to DSC with a receiver via the trainer socket but there was never any evidence that this signal was PCM. I believe it was CPPM a signal because I haven't come across any discussion of the PCM signal being available at the trainer socket, I would say it's likely to be the same on the 8SG, but you will need a scope to be certain.

Oct 16, 2011, 09:26 PM
Registered User


I have a similar problem. I have a FP-T4H transmitter (4 channel with 27 mHz am transmission) which I want to convert to 2.4gHz with a Assan X8D hack module. However, I have not been able to locate a PPM signal on the single board that is there.

Could some body help me in this. If it is not possible to get a ppm signal, I dont mind building up the ppm signal with my own board, but I will need help with a simple encoder circuit. The transmitter mechanism is in perfect condition and the pots are without jitter.

Oct 17, 2011, 10:06 AM
Oxford Panic
AndyOne's Avatar
An oscilloscope is the best way to find a PPM signal if it exists, without one you are effectively blindfolded from an electronic point of view.


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