TKR-850 High/Low Issue

[tweiss3]

I bought a TKR-850 from a local ham that was closing up his radio rental business. He had a stack of 850's in a trunking configuration, complete with controller, amplifiers and combiner. All were operational when I pulled it from the stack and took it hope, though it had been off the air for a little while.

The local community is a wealth of knowledge, and between documentation, phone calls, and a little bit of time, I was able to get the transmitter/receiver tuned up like new. Admittedly, there wasn't much to tuning required. Direct power out of the transmitter side is now 41.0W high and 25.4W low.

When I opened this box, the duplexer was already tuned/marked for 462.575/467.575. There was the factory duplexer alignment sheet sitting on top of the duplexer (attached). I attached my freshly calibrated NanoVNA to the duplexer, with a dummy load on the open port, and they seem to align with the factory sheet (sweeps attached). This "should" work just fine. I'm assuming the minor changes are due to test equipment, and the duplexer is just fine as it was, no adjustments made.

Here is the weird part. I was going to connect it to an antenna in my basement on low power just to test it out around the house and with a few HTs. To make sure I wasn't causing problems with too much RF, I hooked up the power meter with a dummy load to the output of the duplexer and tested on both high power and low power. I knew as a "mobile" duplexer it was "lossy" on high power already as I had tested that, but today, high out of the duplexer was 24.8W and low out of the duplexer was 22.8W.

That is -2.18db loss at high power, and -0.47db on low power. Frequency counter says it is right on frequency. What am I missing that the loss changes so much between power input levels? Looking up the duplexer part number, it's is a 50W rated Icom duplexer (photo attached), so I would assume 41W would be no issue.

Any ideas or help would be appreciated.

If this is more related to another section in the forum, feel free to move it.....

 

[tweiss3]

I will add, it is using the original Kenwood 90 degree cables (have part number on them) in excellent condition. To double check that, I used a brand new 2' N to N jumper cable, and it made no difference.

 

[kd4efm]

I use fiplex duplexers and you should see at 40 watts approx 32 to 34 watt out. The big can (TX/RX) you would see 3 db loss. or 100 in 50 out

To me, sounds like it needs to be tuned again.
as for 25 in and 22 out on low power, that's a bit odd.
if you have a tracking Gen monitor, use that instead of the VNA. I know the Freedom R8200 has VNA
but that is more for line sweeping is I read that right. I have a R800B and Track Gen, but not this VNA stuff.

 

[tweiss3]

I use fiplex duplexers and you should see at 40 watts approx 32 to 34 watt out. The big can (TX/RX) you would see 3 db loss. or 100 in 50 out

To me, sounds like it needs to be tuned again.
as for 25 in and 22 out on low power, that's a bit odd.
if you have a tracking Gen monitor, use that instead of the VNA. I know the Freedom R8200 has VNA
but that is more for line sweeping is I read that right. I have a R800B and Track Gen, but not this VNA stuff.

My expectation was 32 out, but saw a little less. I may have to drop it off at a friend's house, I don't have a tracking Gen monitor or service monitor.

My big concern is why does the loss change so much high to low power? I can understand if the math changed +/- 10%, but such a large change doesn't make sense to me.

 

[buddrousa]

What is the power going into the duplexer
And just a friendly reminder you do have your own fcc assigned license in your name for the frequencies of the repeater. The other option is to have written approval from the owner of the license and use it at the listed site.

 

[tweiss3]

What is the power going into the duplexer
And just a friendly reminder you do have your own fcc assigned license in your name for the frequencies of the repeater. The other option is to have written approval from the owner of the license and use it at the listed site.

Power into the duplexer is 41.0W high and 25.4W low. All power testing was done into a dummy load.

And yes, this covered under my license (GMRS).

 

[buddrousa]

Just for giggles hook it up to HARDLINE and an outside base antenna DB420 Station Master Style not a cheap antenna.
Those duplexers may be hearing the signal

 

[tweiss3]

Just for giggles hook it up to HARDLINE and an outside base antenna DB420 Station Master Style not a cheap antenna.
Those duplexers may be hearing the signal

Actually, it is getting hooked up to 1-1/4" RFS Hardline and either a Laird or Telewave commercial vertical ( I wish I had a DB315). I just need the frost to break, and to make sure the equipment is ready to go into service.

 

[buddrousa]

I have seen in the mobile duplexers do not have enough isolation and the TX gets back in the RX at the shop.
Also seen it when people tried 9913 to feed a repeater.

 

[tweiss3]

I mean, 9913 will technically work, but what is the point in wasting all that energy?

You do bring up a good point, maybe there is something at high power that it reflects from the dummy load and gives a bad reading? I maybe shouldn't be worrying about it, since I wanted to run it a low power to keep it from burning up anyways......

 

[buddrousa]

I have seen desense very bad with 9913 for repeaters.