TK-790H Question

[kg6nlw]

Trying out the Kenwood TK-790H for the 100W capability tonight at 8 PM. I am attempting to wire the DB25 adapter, and this is what I have:

Pins 7, 18 and 25 wire together for (mic/foot pedal) ground.

Pin 1 or 17 is speaker output

Pin 13 is Mic Hot

Pin 11 is Footpedal PTT.


Do I need to do anything special in the FPU to get the radio to behave, or should the foot pedal auto work? Attached is how I have the Function Port currently set up, with Input and Output.


Regards,


-Frank C.

 

[n7maq-1]

You will need to have R640 in place, and R641 open.
Pin 25 is MIC GROUND
Pin 17 is AFO, (low level fixed)
AI1 is Pin 2. Use Pin 7, or 18 as your ground.
And yes Pin 13 is MIC HI

 

[kg6nlw]

I know about R640/641.

The footpedal is what pin then? Pin 11?

Regards,

-Frank C.

 

[n7maq-1]

You have EXT PTT assigned to AI1 (Aux Input) and that is pin 2.

 

[kg6nlw]

Thanks! Now when I key up, I get just a digital noise type output, no voice at all with the DB25. Palm mic still works fine.

Also, which would be "RX Audio out" on the DB25 pins?

Regards,

-Frank C.

 

[n7maq-1]

RX Audio is pin 17, but it is a fixed low level.
What is the mic/tx audio source on your device? Does it need a bias voltage on it?
More info would be helpful.
If you do a search for TK 790 service manual you will find it.

 

[kg6nlw]

XLR microphone into Behringer 1204USB Mixer using the MAIN OUTPUT R for the VHF Radio. XLR to pigtail cable which is wired into a DB25 breadboard type connector for the back of the radio.

A similar setup works fine on the NX-700 but I am needing a bit more power than ~30 watts.

Regards,

-Frank C.

 

[kg6nlw]

For what it's worth, this is what the signal looks like on the input of the repeater as I key up. Maybe this will help?

http://franksrails.com/2025-07-17%2021-44-02.mp4

Regards,

-Frank C.

 

[kg6nlw]

Got that worked out! I had Ext PTT w/MIC Mute turned on in the Optional Features...

Now I just have to figure out why I can get into the repeater but can't hear it back. The squelch is turned down to 0 using the squelch button on the radio...

Regards,

-Frank C.

 

[kg6nlw]

Things are getting weird and I'm not sure WHERE to start. Audio was fine for a bit and now I have this horrible BUZZ behind the audio to the point it makes my voice impossible to hear. The radio also is refusing to key up the repeater. The radio does things FINE when only the palm mic is attached, but that doesn't SOLVE the way I am trying to do things. I am trying to get rid of the palm mic!

What could I have done wrong?

Pin 2 is footswitch hot
Pin 13 is mic audio
Pin 7 is footswitch ground
Pin 25 is mic ground.

Regards,

-Frank C.

 

[kg6nlw]

To add on to this when I go into Program>Tuning and hit TX on 148Mhz, the audio is being passed FINE with no issues at all. Palm mic plugged in and DB25 plugged in, I get issues. Just DB25 plugged in, I get issues, just the palm mic, no issues as seen in this video.

http://franksrails.com/2025-07-18%2011-57-23.mp4

Does ANYONE have an idea or a fix for this? I'm pulling out what little hair I have left! The NX-700 wasn't this difficult!

EDIT ADD: Pic of DB25 connector and how it is wired.

Regards,

-Frank C.

 

[mmckenna]

Where is the antenna located in relation to the radio? Any chance RF is getting into the new wiring?

 

[kg6nlw]

Where is the antenna located in relation to the radio? Any chance RF is getting into the new wiring?

100+ feet away and 25 feet above where the radio sits too! Unless I have some sort of CMC coming back in somehow.

Regards,

-Frank C.

 

[mmckenna]

Maybe try it in to a dummy load, reduce power, etc.

Just guessing here. May be other issues, but that's the first thing I'd check.

 

[AM909]

If you disconnect the wire from pin 13 and transmit, do you transmit dead carrier with no modulation? Are you hopefully testing into a dummy load?

 

[kg6nlw]

Maybe try it in to a dummy load, reduce power, etc.

Just guessing here. May be other issues, but that's the first thing I'd check.

Only one power setting, "high" power at 100W.

If you disconnect the wire from pin 13 and transmit, do you transmit dead carrier with no modulation? Are you hopefully testing into a dummy load?

Correct on Pin 13 with dead carrier/no modulation if I disconnect that wire. I am on Simplex so I'm not bothering repeaters and Simplex is dead in my area.

Regards,

-Frank C.

 

[mmckenna]

Only one power setting, "high" power at 100W.

You can set the channel for low power, should be round 45 watts. That might help if its RF getting into the audio.

 

[kg6nlw]

You can set the channel for low power, should be round 45 watts. That might help if its RF getting into the audio.

Let me try that. I would need to bring it back to 100W, though, eventually.

Regards,

-Frank C.

 

[n7maq-1]

Do you have an oscilloscope? If not there are some on Amazon at a good price for ham use. If so look at the TX audio on pin 13 both connected and disconnected from the radio.

When we would use the ACC port on the 90 series we normally would use an isolation transformer, 90's are a bit picker than the later radios.

Jim

 

[kg6nlw]

You can set the channel for low power, should be round 45 watts. That might help if its RF getting into the audio.

So bumping it to "low" power and then bringing it back to "high" power seemed to fix whatever was wrong...

Do you have an oscilloscope? If not there are some on Amazon at a good price for ham use. If so look at the TX audio on pin 13 both connected and disconnected from the radio.

When we would use the ACC port on the 90 series we normally would use an isolation transformer, 90's are a bit picker than the later radios.

Jim

I do not have my own oscilloscope. I already have an isolation transformer in line between the radio side and the mixer board.


Now onto the next issue...I can't hear the repeater coming back to me on this radio, but I can on other radios. I can get into the repeater just fine with the radio and the PL isn't needed on RX, just TX. Switching the coax between Radio A (TK-790H) and Radio B (NX-700) isn't feasible with ease and I can't put up another antenna.

Regards,

-Frank C.