Late last year I decided to tweak up the AA4VU UHF repeater using an IFR 1500 service monitor. I was dissatisfied with the performance of the repeater, even though I had tuned the duplexer and front end of the receiver prior to installation. I decided to try a different tactic, and decided to use a return loss bridge between the IFR & the repeater gear. With the RX frequency programmed into the IFR and watching the analyzer display, I tuned the receiver front end for best match (highest return loss or deepest notch on the screen). It made a terrific difference...we gained several dB of sensitivity. Then I turned to the TX & RX cans and again tuned for best match; first the RX path then the TX path, each time with the opposite set of cans terminated into 50 ohms. I also looked into the output of the transmitter and tweaked it for 50 ohms at the TX frequency (powered off) As a last step, I reconnected the repeater and looked into the system from the antenna port. I touched up the RX & TX paths just to ensure best match. By the time I was finished, we gained ~12-15 dB of sensitivity.
On my way home that night, I was able to get into and hear the repeater from a distance of 10-12 miles further than previously.
At 05:04 PM 3/22/2005, you wrote:
I used to tune them that way also, and thought I did well, but after I got access to a Spectrum Analyzer with tracking generator, I find it much easier and more accurate. Maybe because the pattern is visual when you are tuning with the tracking generator and analyzer. I've taken duplexers I tuned the old way and put them on the service monitor and found I could get 8 or 10 db better with the analyzer. You use what you have, and I sure would use the analyzer/generator combination if I had it.
Gary - K7NEY
- ----- Original Message -----
- From: Michal Smialowski
- To: [email protected]
- Sent: Tuesday, March 22, 2005 10:55 AM
- Subject: [Repeater-Builder] Spectrum Analyzer
- I have always tuned duplexers just using a signal generator and a radio receiver. Peaking the passband and then going for the deepest notch for the reject. Although this seems to work, the results haven't been spectacular. I realize that there are many variables to consider. My question is, does using a spectrum analyzer and a sweep generator ( I am guessing here) make the process better, and if it does, how so ie what is the principle behind it?
- Thanks
- Mike Smialowski
- VE7SML
- Smithers BC Canada
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Robin Midgett K4IDC
2004-2005 President, SVHFS
2005 SVHFS Conference
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