FL760 Transmit Issue

[aganjoo]

Hi Folks

Need some guidance here.

I am using FL760 Radio and Flightcom 403 intercom. While testing transmit function today, I discovered that it is not working and no one can hear my transmissions. You can hear the PTT tone and the light turns red on the radio but it seems that the audio is not modulated in the transmit mode. The receive side on the radio is working fine and I can hear the transmissions from other users on the same freq but I am unable to transmit

The intercom function from 403 is working fine and I can communicate 2 way with the passenger.

Any suggestions on what might be happening? Did anyone encounter this issue?

Thanks

Amit

[daleandee]

I am using FL760 Radio and Flightcom 403 intercom. While testing transmit function today, I discovered that it is not working and no one can hear my transmissions.

Hi Amit,

Don't know if I can offer any guidance but here goes ...

Try another headset and be sure that the headset you use has an electret microphone (see instructions page 13 under helpful hints). You might try bypassing your intercom and wiring the mike direct to the radio in reference to the wiring diagram. Also note that the 760 has a dedicated microphone ground wire (# 2 pin) in addition to the PTT switch which is grounded with the switch to complete the microphone circuit.

There is also a microphone gain setting inside the radio but I wouldn't think that would be the cause unless someone has been inside the radio since it was received from the factory. If the microphone is working through the intercom and the red light on the radio is on then it appears that either the audio line between the intercom and the radio is not correctly connected or there is damage to the final output of the transmitter most likely caused by keying the radio without an antenna connected or the antenna is not tuned to a descent SWR (need a meter to check this) resulting in a transmitted signal that is very poor. An antenna with a bad SWR reading will still receive fairly well.

Hope this helps.

Dale
N319WF

[aganjoo]

Thanks for your inputs Dale

I have tried multiple headsets with electret mic. Do you know how to check/change the microphone gain settings on the radio. I cannot seem to find the details on that

[daleandee]

Thanks for your inputs Dale

I have tried multiple headsets with electret mic. Do you know how to check/change the microphone gain settings on the radio. I cannot seem to find the details on that

Hi Amit,

I was afraid you'd ask that. Before changing headsets my radio was picking up too much through the mic and I wanted to turn my mic gain down. I called a dealer but don't recall who and where they were.

From my old and failing memory I *think* the information he gave me was that the component was labeled "RM06" and was located near the right rear side of the radio. I never took the cover off of my radio as using the the Clarity Aloft headsets cured the concerns I had with the hot mic.

I truly would doubt that the mic gain is the concern. I would tend more to think that you have either an antenna with a very high SWR, or (worse case scenario) the final output transistors in the radio have been damaged by keying the radio up without a load on it. In my case I have a friend that has the equipment to check both the antenna SWR (Standing Wave Ratio) and the wattage/modulation of the radio output. The radio, as sent from the factory, is set to be quite impressive both on power and modulation.

I wouldn't open the radio until all other options have been exhausted.

Dale
N319WF

[rizzz]

Last night I fired up my electrical system for the first time and I have an FL760 as well.
It works great, I get load and clear receptions and transmissions.
I used the pre-wired harness from Spruce though so hooking it up was a no-brainer for me.

Anyway, you can find the manual here: http://www.illinigliderclub.org/poh/FL760.pdf
On page 10 you can find how to adjust the automatic VOX gain, it talks about adjusting slidetone & volume microphone gain as well but there are no instructions on how to do this.

[Rick524]

Hi Amit, I've looked at the schematics for the 403 and FL760. Check for this......

on the 403: pin#2 pilot mic in
pin #3 co-pilot mic in
pin #6 co-pilot ptt in
pin#7 pilot ptt in
pin#8 ptt out to comm radio (to pin 7 on FL760)
pin#16 co-pilot tx audio (to pin 3 on FL760)
pin#17 pilot tx audio (to pin 1 on FL760).
The Mic audio lines have to match with the ptt lines, eg: pilot mic audio and pilot ptt. co-pilot mic audio and co-pilot ptt.
If you have the ptt input lines crossed, you will have transmit carrier, but not tx audio. Your intercom function will still work though. This sounds like the problem you're having.

Hope this helps.
Rick
Sonex 524

[aganjoo]

Gents

Thanks for sharing your thoughts as well as suggestions

I will try out some of these when I get back in town in a couple of days

Thanks

Amit

[Judoka5051]

Hey Amit,

I started out with the same radio and it worked fine for about a week, then I had the same problem that you're having except that I got loud static in the headset when transmitting. After wasting lots of time changing every other thing I could (antenna, coax, wire harness, ptt switch) before giving up and buying a different radio. I bought an Xcom and I can't believe the difference! It's a great radio and has the best intercom I've ever used built right in. It was a little pricey (for me) but worth every penny.

Lance