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Sep 13, 2008, 02:41 AM
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BushmanLA's Avatar

RSSI pins for various receivers

Changed the title of the thread since so many nice folks are pitching in their knowledge.

I couldn't find the info on this for myself so I figured I'd post my results for those of you who are interested.

The R168DF is an 8 channel PPM receiver, and the R168DP is a PCM receiver. Both use the same 31136 FM detector IC. You can find a datasheet for a very similar (if not identical) device if you search for TA31136FG.

The RSSI pin is pin 12 on the 16 pin device. This is the 4th pin from the top right of the chip.

The pin outputs a DC voltage level is about .7V with the transmitter off and 2.2V when the transmitter is on. You can use this to tell the signal strength that the receiver is getting, but keep in mind that it doesn't tell you anything about signal quality, or if it is your Tx it is hearing or some other guy's Tx a mile away. Also remember that it probably saturates fairly easily, meaning it doesn't take much to make it hit that top 2.2V mark. With my antenna collapsed and on the other side of the house I was reading about 1.8V

Other folks who know more about this stuff should feel free to correct any misconceptions I have here.

There is no nice large pad to solder on to here, there are some small vias in the board and I used one of these to tap on to. I used a micro drill bit to clean it out and then used some magnet coil wire to go through it and soldered on. Don't forget to sand the enamel off the coil wire

There are two vias you can tap onto but the one next to the capacitor was the easiest to get to.

(see attached images)

I couldn't see the via from both sides here and since there was a large solder pad available on the back side I just used that. There may be other tie in points but I didn't bother once I saw the pad. There is plenty of room for a wire to lay on the under side of the board inside the plastic casing. I drilled a little exit hole near the rim of the case.

(see attached images)

If you want to do some real testing on what kind of things increase or decrease your signal range this should be helpful to you. Enjoy.
Last edited by BushmanLA; Jun 11, 2012 at 08:07 AM.
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Sep 13, 2008, 05:14 PM
Flying FPV from the lab.
aaron_gx's Avatar
thank you! I have the 168df. I shall try it out. It'd be nice to incorporate RSSI to an OSD, or a small volt meter you could look at with camera while flying.
Sep 14, 2008, 05:38 AM
Registered User
Think I'd go for the small volt meter seen by camera movement myself trouble is..I can things up enough without taking a receiver apart!! Good mod though if you are competent.
Last edited by ROSSMANS; Sep 14, 2008 at 05:43 AM.
Sep 14, 2008, 11:22 AM
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typicalaimster's Avatar
And if you're looking for RSSI out on a R617FS it's Pin #28
Last edited by typicalaimster; Sep 14, 2008 at 11:35 AM.
Nov 21, 2008, 11:54 PM
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sokiii's Avatar
Does anybody know where RSSI pin is on R319DPS?
Last edited by sokiii; Nov 22, 2008 at 06:23 PM.
Nov 22, 2008, 06:56 PM
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sokiii's Avatar
Here is the RSSI for Futaba R149DPS

But "unfortunately" I bought R319DPS. Looks like it has the same chip. I have an idea to measure voltage on every pin of chip, I have to be very careful. Does anybody know better way?
Nov 22, 2008, 11:55 PM
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sokiii's Avatar
I played a little bit with RSSI signal from R168DF receiver and found it changes from ~2.2V to ~0.7V with the degradation of RC signal. I have onboard voltmeter which is connected to OSD, but internal resistor of voltmeter is only ~70 kOhms. So when I connect RSSI pin to it the voltage range is changing to 1.3V-0.4V.
I still can monitor the signal strength but is it bad for receiver to load RSSI pin? If yes I think I need micro current amplifier with big input impedance. Where can I get it or any recommendation how to build it?
Nov 23, 2008, 06:28 PM
"Here birdy birdy birdy..."
MDreamer's Avatar
Does anyone know RSSI pinout on any JR/SPEKTRUM Rx?
Jan 25, 2009, 07:52 AM
Suspended Account
For the R319DPS the RSSI pin can be found at the below solder pad, where the red arrow is pointing at. This will output a voltage between 0.7 and 2.2V, with 0.7V being the absence of any signal and 2.2V with the transmitter nearby (hence maximum RSSI value).


May 19, 2009, 07:20 AM
Registered User
I have a R149DP but unfortunately it is a different revision to the one linked to above.
Any ideas where the rssi port is on this one?
May 19, 2009, 10:09 AM
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BushmanLA's Avatar
Originally Posted by sokiii
I still can monitor the signal strength but is it bad for receiver to load RSSI pin?

Do NOT significantly load the RSSI pin. By load I mean draw current from it. Which means if you attach anything to it, it needs to have a very high resistance. A few 100k Ohms at least I should think.

I know on my PCM receiver, if I goof with the RSSI pin I can cause the thing to failsafe. So be careful what you do or you might have a reduction in range.

The best bet is to buffer it with a voltage follower. Or some kind of buffer setup.
May 19, 2009, 12:52 PM
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sokiii's Avatar
Originally Posted by BushmanLA
The best bet is to buffer it with a voltage follower. Or some kind of buffer setup.
That's exactly what I did (half a year ago).
May 20, 2009, 04:28 AM
Outta Sight
Originally Posted by nick.sargeant
I have a R149DP but unfortunately it is a different revision to the one linked to above.
Any ideas where the rssi port is on this one?
LHS of the chip, bottom pin, directly above the Futaba F.
Aug 28, 2009, 01:05 AM
Registered User
According to this thread ( ) RSSI pin of new R149DP (FP6302B chip) is located on bottom of chip, second pin from the left.
Can someone could confirm?
Is there a better location to solder than directly on chip's pin (solder pad for example )
Aug 28, 2009, 01:36 AM
Registered User
I really wish I understood what you were doing. Im right at the point of being able to read signal strength from your OSD. lol

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