Link TKR850 to TK790

[otobmark]

I’m trying to use TK790 as a link radio for a TKR850 repeater being used for a deployable asset. In our use we need power on vhf.
My preliminary observation/suspicion is that the audio is not a clean match between radios. Maybe issues with pre-emphasis de-emphasis.

 

[Project25_MASTR]

I can tell you from a project I am currently working on involving full duplex link TKR-850's that the audio lines are high impedance unbalanced on the accessory connector. The solution to interface them to VHF Quantars (which are replacing TKR-750s) was to use an ARCOM R210 to normalize the audio interface.

 

[ramal121]

What audio ports are you using? Should be MI for tx and AFO for rx on the 790. For the TKR850 you would use TA and RA. What exactly is the issue with the audio?

 

[otobmark]

What audio ports are you using? Should be MI for tx and AFO for rx on the 790. For the TKR850 you would use TA and RA. What exactly is the issue with the audio?

I’m not sure there is a problem, I just suspected there would be. The vrms was different. My only linking experience is with acu gateway device.
Need something working if imperfectly by end of week. Later I’ll have time to dial it in optimally. I was hoping someone had already done this setup before and could tell me how he did it and the results.

 

[ramal121]

Well if you're under the gun to get this done you'll have to do this down and dirty. I second using some kind of controller to give you audio leveling, time out timers and remote control just in case. I have tried the Arcom 210 but found them difficult to set up and the firmware is a bit buggy. Fine for hams. I switched to the ICS Linker IIa. A little cheaper, easier to set up (DTMF only though), and works well. Always liked NHRC controllers but they are now out of business.

So lets talk. First the logic. You need to cross the PTT to an I/O output "TOR" on each other radio. That's pretty straight forward.

Then the TKR RA output (about 400 mVrms) to the MI input of the 790 (5mVrms). Since the 790 is so sensitive on its mic line I use a series 10K resistor to pad the audio down. This puts the MI line into a range that adjustments can be achieved. The TKR RA output can be adjusted in the test mode of the software.

On the other side the 790 AFO out (125 mVrms) would go to the TKR TA input (280 mVrms). This is a mismatch that you can't do anything about without a little boost from on the 790 (reason for a controller). It may work with reduced deviation, you'll just have to see if it's acceptable. I have had issues connecting the 790 AFO line to certain equipment due to the DC bias on this line. The TKR states that it is AC coupled but a series cap of say 1.0 uF never hurts. The TA line is also adjustable in the test mode but I would think you'd leave this at max.

All audio lines are <1K ohm so impedance matching is not really a factor.

A couple of male DB-25's, shielded cable and programming should get you going.

 

[otobmark]

OKAY, can do all that. Since I’m not up on cps I assume I will need to select a programmable pin on 790 to set for PTT since I don’t see a dedicated pin for it. I would connect that to the squelch busy L pin on 890.

 

[otobmark]

I finally checked my PM’s ramal121. Found a guy who had experience poking around in the insides of old KW. Understood your notes at once.

 

[WB5ITT]

I can interface anything to a TKR750.....Ive had a TK7180 link radio on a TKR750 for years.....TK790 is no really any different....if I can be of help, let me know..

 

[otobmark]

I can interface anything to a TKR750.....Ive had a TK7180 link radio on a TKR750 for years.....TK790 is no really any different....if I can be of help, let me know..

Might need help later. Our local TF deployed to Vermont for swiftwater rescue etc. and I need to find out how well all their comm gear worked and what they used. They talked about going to basic DMR kenwoods for cashe use which would mean moto repeaters mostly. So far analog reigns on field setups...lowest common denominator.