Futaba RF Module Pinout - RC Groups
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Jun 28, 2005, 01:01 AM
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Futaba RF Module Pinout

I'm working on a personal project and I'm trying to figure out the middle pin of this module(FP-TP-FM), so far I've come up with(looking at the back of the radio, with the module board installed, and calling the left most pin "1")

1 - PCM/PPM Signal from Radio
2 - V+
3 - ??
4 - GND
5 - RF Out

I'm not sure what pin 3 is, the signal on it looks like a weak copy of the RF out signal, is it perhaps the pin used to indicate to the radio that the module is plugged in? I'm going to throw it on a better scope at work and see what I come up with. Any help would be greatly appreciated.
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Jun 28, 2005, 06:16 AM
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Bruce Abbott's Avatar
Pin 3 is the RF output indicator. It pulls down to ground when RF is detected at the collector of the final amp.
Jun 28, 2005, 09:34 AM
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Thank you very much!
Jun 29, 2005, 04:31 AM
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Hi , Bruce
Do you have the full schematic of futaba rf module?
Jun 29, 2005, 06:07 AM
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Bruce Abbott's Avatar
I have traced out the circuit of 60MHz unit, but only the part posted above has been translated into electronic form (the original drawing is very messy and may even be wrong in a few places).

Here is another drawing that I found on a Russian website. It's tidier than mine, and possibly more relevant as it shows a 72MHz version.
Jun 30, 2005, 03:06 AM
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thank you ,Bruce.
Jun 30, 2005, 09:59 PM
I'd rather be flying...
I have a 9C on 50 MHz and I have access to a Spectrum Analyzer. My 9c is transmitting on 50.86 and it should be on 50.88. Can someone tell me which pot(s) in the RF module to tweak to bring it in line?

Lew H.
Jun 30, 2005, 11:26 PM
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nOKJF, I guess there is nothing wrong with your RF Modules......your transmitter is operating at 50.880 MHZ, but your Spectrum Analyzer is reading at 50.86, I guess the 20 Khz offset is due to the PPM modulation....you have to remove the modulation in order to get an accurate operating frequency....its a complicated task of tuning the Transmitter modules.

its not just simple removing the PPM modulation signal, you have to inject a proper modulating signal.

I guess, the absolute accuracy is not important here, its the Matching or Tuning of your receiver to its Matching Transmitter Modules.

If anybody know the procedure, about tuning the transmitter modules, It would be very interesting leard.
Jul 01, 2005, 02:42 AM
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I don't think so, remote control is narrow band, it only has no more than 10k bandwith, it should within 50.880M + 3k and 50.880 - 3k.

Isn't it ?
Jul 01, 2005, 07:07 AM
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Man's Avatar
I have a FP-7UAPS transmitter. Recently, I had turn on the transmitter and found out there was not RF output. I immediately put another RF module for test. It is still not RF output. After reading Bruce Abbott’s full schematic of Futaba RF module, I tested transmitter pin 2 and pin 4; it is found that the pin 2 does not have any DC supply. I prepare to send the transmitter to Futaba for repair but they have already stopped to repair FP-7UAPS in 2003.
Can anyone help ?
Jul 01, 2005, 07:11 AM
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Icedog, Yes, your right a 20 Khz difference is too large....any way my point is you can not just measure the output frequency with ppm signal modulating the carrier......the ppm signal has to be converted to steady constant DC voltages.......or a ppm can be replace by a 50% duty-cycle square wave, and using Spectrum Analyser to adjust for minimum side band splatter.

I guess a frequency counter would be a better equipment to check the Transmitter output frequency......by just putting the Futaba Transmitter near the Frequency Counter, you can monitor the actual frequency output, this will only work on PPM/FM only. my Frequency Counter can not lock on frequecy using PCM mode, I think due to PCM signal, that produce a random like signal that make difficult for frequency counter detect.

MAN, your problem might be due to PCB break in the terminal post that connect the Transmitter Modules and the Transmitter.

due to frequent INSERT and REMOVE of Transmitter Modules, the TERMINAL POST tends to create a hairline Break......lots of FUTABA 7UHP or FF7 owner experience this problem and cause Crashes. I use to have the 7UHP transmitter also, I have added an additional Stranded wire, by directly soldeing the wire from the Terminal post to the circuit.

all 7UHP and FF7 transmitter use a SINGLE SIDED PCB, this can cause a Hairline Crack on PCB.....its nice to know the FUTABA have already improve on the 9CHP transmitter, they use DOUBLE SIDE PCB, to avoid this problem any more.
Last edited by lazy-b; Jul 01, 2005 at 08:55 AM.
Jul 01, 2005, 10:01 AM
I'd rather be flying...
To 20 KHz difference first showed up during a range test with a new receiver, we only got about 65 feet. After that we looked at the Spectrum Analyzer and saw it was calling the center 50.860 MHz. Anyway, I hate to just play around with unknown pots just to see what it does without knowing the potential side effects. We checked on PPM and PCM and it centers on 50.860 MHz on both. With the poor result on the range check, 20 KHz clearly makes a difference.

Thanks for the thoughts,

Lew H
Jul 01, 2005, 09:40 PM
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Bruce Abbott's Avatar
20KHz isn't just a bit off, it's on another channel! Your receiver should not be responding at all. Before trying to retune, I suggest verifying the TX crystal's frequency. If the paper label is correct, peel it off and check that it matches the frequency marked on the can .

If the crystal is OK and the frequency really is 20KHz off, there is probably a fault in the modulator circuit which should be fixed rather than masked by retuning (assuming it is even possible to adjust out that much error). Bearing that in mind, here is the tuning procedure...

The modulator has two trimpots for adjusting the high and low frequencies, typically + and - 1.5~1.8KHz from the channel center frequency. Note that so-called 'FM' R/C transmitters actually use FSK (Frequency Shift Keying), therefore there is no adjustment for center frequency.

You need to disable the normal PPM/PCM input and apply fixed high and low signals. It may be possible to do this through the trainer port. When the PPM input is high, one pot will be more sensitive than the other. Trim the sensitive pot for the high frequency (eg. 50.8818MHz), then set the PPM input low and trim the other pot for the low frequency (eg. 50.8782MHz). Repeat until both high and low frequencies are correct. Your frequency measuring device should be accurate to +-100Hz or better.
Jul 02, 2005, 07:50 AM
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Man's Avatar
lazy-b, I have tested PCB side of the RED pin and BLACK pin next to the TERMINAL POST and also does not have any DC supply. The problem still cannot be solved.

Thanks for your advice.
Jul 03, 2005, 04:50 AM
Registered User
Check wires to the module board... all the way back to the regulator

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