Duplexer info

[airboss20]

I have a 4 can duplexer that I field tuned on my repeater. I am using a Motorola RKR1225, and before the duplexer was placed in line I could get 50 watts thru my RF Amp on 9 watts TX on the radio. After the duplexer was placed I have the output power on my radio set to max and I can only get 37 watts out after the RF Amp and duplexer. I expected some loss thru the duplexer, but this seems excessive. Anyone know how to remedy this issue.

BTW, when I field tuned, I used my signal generator and a portable receiver hooked to each can individually.

 

[fineshot1]

I have a 4 can duplexer that I field tuned on my repeater. I am using a Motorola RKR1225, and before the duplexer was placed in line I could get 50 watts thru my RF Amp on 9 watts TX on the radio. After the duplexer was placed I have the output power on my radio set to max and I can only get 37 watts out after the RF Amp and duplexer. I expected some loss thru the duplexer, but this seems excessive. Anyone know how to remedy this issue.

BTW, when I field tuned, I used my signal generator and a portable receiver hooked to each can individually.

Generally when asking this type of question it is best if you supply
the band or freqs of operation and make/model of duplexer and also
the type of cables you are using, however the rf loss through the
duplexer you described above does not seem too excessive.

I have a 220 Mhz repeater with a Telewave Notch/Pass duplexer and get
50W out of the amp and about 38W out of the duplexer with all
of the cans tuned properly.

 

[KR4BD]

I also have a 222 repeater and get about the same results. There is power loss incurred going through duplexers. In my case....about 10-11 watts into the duplexer and 8 watts out.

 

[ramal121]

Insertion loss in a duplexer varies with the separation of TX and RX frequencies. The closer they are together, the more insertion loss you'll have. Some TX combiners go as high as 3dB loss, but with all that is connected to them, this would be considered normal.

Maybe if you gave us a freq spread and what type of duplexer (Pass, notch, or a BpBr hybrid) we might be able to help you. But shooting from the hip, 50w in and 37w out wouldn't be too far out of the question as that is about 1.3dB insertion loss.

 

[davidgcet]

agreed, that is not bad as a general figure. i've had duplexers with less than .5db loss, then again i've had some with over 4.5db of loss due to VERY close freqs!

 

[zz0468]

I have a 4 can duplexer that I field tuned on my repeater. I am using a Motorola RKR1225, and before the duplexer was placed in line I could get 50 watts thru my RF Amp on 9 watts TX on the radio. After the duplexer was placed I have the output power on my radio set to max and I can only get 37 watts out after the RF Amp and duplexer. I expected some loss thru the duplexer, but this seems excessive. Anyone know how to remedy this issue.

BTW, when I field tuned, I used my signal generator and a portable receiver hooked to each can individually.

50 watts vs. 37 watts is 1.3 db. That's pretty damned good. Is maximum power output 50 watts, or is it actually more? Your post is a bit ambiguous so it's really hard to say if you have a problem or not. 1.5 db or so is pretty typical, so off the top of my head, I think it's ok. Have you made any desense measurements?

While it's possible to tune a duplexer with a receiver and a signal generator, the best way is to sweep it.

 

[airboss20]

Got it. I was able to fine tune the tx side of the UHF duplexer cans by using 2 wattmeters. I placed a wattmeter between radio and duplexer tx showing reverse power, and another between duplexer and dummy load showing forward power. I fine tuned the plungers on the cans while transmitting on 5 watt low power to get to the sweet spot between tx and reflected power. Then when satisfied I increased my tx power until i was able to get 50 watt out on antenna side of duplexer. This is set up for GMRS repeating and I am limited to 50 watts, and the duplexer is capable of 100 watts. Now everything sounds great. I have no desense noise and am still able to transmit full power.

 

[petnrdx]

Sounds like it is working about normal, depending on the model.
Duplexer designs vary GREATLY, and manufacturers quality varies also.
One or two dB of insertion loss is pretty common on reject and pseudo-pass reject at VHF with a mhz or so of spacing.
A bit less insertion loss at UHF with its 5 mhz spacing.
Most "true" band pass/band reject get closer to 3 dB. Some are better, but just below 3 dB seems the most common spot in the several hundred I have worked on.
Closer the spacing, the higher the insertion loss, and the more isolation you need, the higher the loss.
As for TX combiners, 3 dB is actually pretty low.
I have worked on some that were over 10 dB.
In Land Mobile you OFTEN can't get a new freq, so you must use what you can get licensed for.
And if the site you need has others using up a lot of antenna space, then you may have to combine/multicouple.
Better to get 10 watts in the air ( for 100 at the TX ) than not have coverage at all.
If you can find out the model number of the duplexer, likely someone here can tell you exactly what it should do.
Then again, it sounds like it is working.
Unlikely you would get it a lot better than it is.
If you have no desense, and the PA likes the load presented buy the dupe, why mess with it further.

 

[airboss20]

My thoughts exactly petnrdx. I have it set up at my house with a roof mounted Workman UVS-200 Dual Band antenna with 8 db gain on UHF. It is about 6 feet tall. I am currently getting roughly 8-10 mile radius as it is. When I get it on the hilltop I will have a Workman UVS-300 that is 17 feet tall mounted on a 25 foot tower. The UVS-300 is actually a Dual Band antenna, but I picked it up brand new at the hamfest last year for $75, AND it has 11.5 db gain on UHF. I think that will boost my RX/TX just a little.

Overall I am very happy with my tuning job on the duplexer. If I can hear a 4 watt portable from 8 miles away from an antenna mounted on my roof while duplexing, I think I'm pretty close to dead nuts.

I do appreciate everyones input on this thread. It is a great help to tinkerers like me who like to play with this stuff and learn as I go.

Thanks!

 

[Skypilot007]

Be careful with those Workman antennas. My UVS-300 leaked a ton of water into it. They need to be sealed with silicone between the mid section and the bottom section, unless they have made a design change. I also had swr issues with it before it got wet. I would test it first before installing. Also they are not tuned very well for GMRS. My swr was just over 3:1 at 462 and 467 MHz.