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Author Topic: Tuning a mobile duplexer  (Read 2601 times)

KK6RPX

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Tuning a mobile duplexer
« on: January 23, 2019, 03:26:58 PM »

Hi All,

Proud new owner of a Rigol DSA815TG spectrum analyzer here. I have never used one before and my first project is tuning a mobile UHF duplexer that has had the "golden screwdriver" applied to it in the past. I seem to be able to get a little better than -100dB of isolation from it. I just want to make sure I am doing this correctly.

The duplexer has three ports, marked LOW, ANT and HIGH. Let's say I want to do a 5mHz positive offset with 442 being the RX frequency and 447 being the TX frequency. I connect the TG output to the ANT. To set the RX side of the duplexer I would connect the analyzer input to the side marked LOW, terminate the HIGH side with a 50 ohm terminator and set the frequency to 447,  then tune for greatest isolation. Then connect the analyzer input to the HIGH side, set the frequency to 442 and tune for greatest isolation. Correct?

This is FUN!
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K4JJL

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RE: Tuning a mobile duplexer
« Reply #1 on: January 24, 2019, 06:30:03 AM »

Sounds like you got it.  I put labels on the TX and RX ports with the pass and reject frequencies.  Helps me keep it all straight as I'm moving the cables around and keying the freqs in my service monitor.
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KK6RPX

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RE: Tuning a mobile duplexer
« Reply #2 on: January 24, 2019, 06:43:06 AM »

Thanks for the reply! Now I just need to figure out how to tune the band pass of a TKR-830 but I can't seem to find a manual or any service info for this repeater. I'll put up a post about that.
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NA4IT

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N2AYM

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RE: Tuning a mobile duplexer
« Reply #4 on: January 24, 2019, 07:53:14 AM »

Thanks for the reply! Now I just need to figure out how to tune the band pass of a TKR-830 but I can't seem to find a manual or any service info for this repeater. I'll put up a post about that.


It is possibly similar to the 850 just a lower power version.
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KK6RPX

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RE: Tuning a mobile duplexer
« Reply #5 on: January 24, 2019, 10:11:13 AM »

Thanks to both of you, the link is useful and I'll go find the manual for the 850.
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KA5IPF

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RE: Tuning a mobile duplexer
« Reply #6 on: January 24, 2019, 12:48:55 PM »

Thanks for the reply! Now I just need to figure out how to tune the band pass of a TKR-830 but I can't seem to find a manual or any service info for this repeater. I'll put up a post about that.


If it's like the front end on a TKR750 it's broad as a barn door.
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PY2HR

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RE: Tuning a mobile duplexer
« Reply #7 on: July 20, 2019, 12:15:45 PM »

Hi All,

Proud new owner of a Rigol DSA815TG spectrum analyzer here. I have never used one before and my first project is tuning a mobile UHF duplexer that has had the "golden screwdriver" applied to it in the past. I seem to be able to get a little better than -100dB of isolation from it. I just want to make sure I am doing this correctly.

The duplexer has three ports, marked LOW, ANT and HIGH. Let's say I want to do a 5mHz positive offset with 442 being the RX frequency and 447 being the TX frequency. I connect the TG output to the ANT. To set the RX side of the duplexer I would connect the analyzer input to the side marked LOW, terminate the HIGH side with a 50 ohm terminator and set the frequency to 447,  then tune for greatest isolation. Then connect the analyzer input to the HIGH side, set the frequency to 442 and tune for greatest isolation. Correct?

This is FUN!


Could you use Rigol DSA815TG?

Att.
PY2HR Moises C.
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KK6RPX

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RE: Tuning a mobile duplexer
« Reply #8 on: July 20, 2019, 12:47:05 PM »

That is exactly what I was using.

I also learned how to normalize so the actual isolation I was getting was about 75dB. I am using it on a GMRS repeater setup and it works OK.
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W9IQ

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RE: Tuning a mobile duplexer
« Reply #9 on: July 20, 2019, 01:55:55 PM »

The repeater-builder site has good tuning information for your UHF notch filters:

http://www.repeater-builder.com/antenna/notch-duplexer-tuning.html

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KB8VUL

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RE: Tuning a mobile duplexer
« Reply #10 on: July 22, 2019, 10:17:35 PM »

On a side note to testing after tuning a duplexer.  If you have a service monitor that will generate a known signal level into the receiver, you can set it to about -90dbm and get the receiver to hear you and key up.  Once the repeater is up decrease the signal level into the receiver and see if the receiver sits and quits hearing you dekeys the repeater and then hears the signal again and keys back up without increasing the signal level.  If the duplexer isn't tuned right the repeater receiver will ping-pong going up and down as the transmitter desenses the receiver due to poor isolation.
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NJ1K

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RE: Tuning a mobile duplexer
« Reply #11 on: August 02, 2019, 10:04:33 AM »

When I tune duplexers I usually place a 6 dB pad at the duplexer on both input and output so that the tracking generator as well as the spectrum analyzer both see a 50 ohm termination. It helps reduce reflections that can skew your results.

You may have already done this. 
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W9CN

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RE: Tuning a mobile duplexer
« Reply #12 on: August 04, 2019, 09:43:50 AM »

Telewave video on how to correctly tune one of their pass reject filter.

https://www.youtube.com/watch?v=tD1upx4-DDI

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W9CN

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RE: Tuning a mobile duplexer
« Reply #13 on: August 04, 2019, 09:48:10 AM »

Sinclair Video on tuning a duplexer

https://www.youtube.com/watch?v=U7QZzzB2LZU
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