Kenwood TK-790H and Firecom Intercom

[rellis73]

We have recently installed a Firecom intercom system with headsets into one of our fire apparatus and we are trying to interface it with a Kenwood TK-790H. The instructions say that for the radio to work properly we have to program the radio to accept a PTT on pin #6 of the 12 pin accessory port and also that it has to ignore the hook switch. I have the programming software and cables for this radio but there is nothing in the programming that looks exactly like this. I did find however a programming option that says "Ext PTT w/ MicMute" and "Off Hook Decode". Does anyone know if in fact these are the two items that the instructions say I am looking for?

Thanks

[jim202]

If I can make a suggestion in not using the 12 pin accessory connector, but use the DB25 connector
on the radio. This is a standard connector that you can obtain from any place. It has a better selection
of signals and controls. Plus it is a much better connector to secure your cable with and you don't need
any special connector or pins and a crimp tool for them.

If you go into the software and read the radio. Then at the top of the screen, left click on the "EDIT"
selection on the top line. Then left click on the "FUNCTION PORT" selection. In the "INPUT" tab,
the line that says "RADIO 1 AI1" should be set to "EXT PTT".

This gives you on the DB25 connector, pin 2 is PTT, pin 13 is mic audio high, pin 17 is RX audio high
and pin 18 is ground. I would recommend that you couple the RX audio with a 1.0 uf cap.

Hope this gives you what you want.

Jim

Originally Posted by rellis73

We have recently installed a Firecom intercom system with headsets into one of our fire apparatus and we are trying to interface it with a Kenwood TK-790H. The instructions say that for the radio to work properly we have to program the radio to accept a PTT on pin #6 of the 12 pin accessory port and also that it has to ignore the hook switch. I have the programming software and cables for this radio but there is nothing in the programming that looks exactly like this. I did find however a programming option that says "Ext PTT w/ MicMute" and "Off Hook Decode". Does anyone know if in fact these are the two items that the instructions say I am looking for?

Thanks

[ramal121]

I concur with jim202, but if you are commited to plugging into the control head, here are the pins:

2 12vdc power (1A max)
3 ground
4 mic input
5 mic ground
6 aux input 1
10 speaker
11 speaker

Go to EDIT>FUNCTION PORT>INPUT>HEAD1 AI1 and program EXT PTT (for pin 6).

Enable OFF HOOK DECODE if you choose, but do NOT enable MIC MUTE W/PTT as this is for data applications only!

In the FireCom, set receive leve to your liking and the PTT delay (monitor function) to minimum time delay.
Set the 2 dip switches for the lowest mic drive level. Turn mic drive pot CCW, transmit and turn pot up until transmit volume just comes up to max volume and no more.

Big gotcha is the KMC27 mic for the 790. Its mic element is hot during any PTT source which means if you key the radio with headset, the palm mic is sitting there picking up engine noise, siren or whatever. Makes the transmission sound lousy. Two fixes: leave the palm mic off, or do the hot mic modification that is not for the faint of heart.

[rellis73]

I thank both of you for your replies and since I have already connected the unit to the 12 pin connector I am going to try that route first. But if I have problems (and for the next truck) I have a better option with the DB25 connector. Again, thanks for the help!!!