Re: VHF MTR2000 Poor Receive Performance
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I think we need to redefine 'deaf'. What are the current 12dB SINAD 1) at the receiver port, and 2) at the antenna port of the duplexer? (Those values were previously reported as 0.40 and 0.53 uV respectively.)
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Originally the problem was reported as " basically deaf to 5 watt portables barely a mile from my house, mobiles work a bit further" and about 1 dB of desense was reported. We need to make sure we're comparing apples to apples. At this point, portable or mobile coverage and anything to do with the antenna system (except the duplexer) needs to be OUT of the equation. Measurements all need to be made using the same test cables and the same signal generator/service monitor. Anything else introduces errors/uncertainties. The receiver itself (with no TX engaged) needs to be baselined to see if it meets specs (0.35 uV for 12 dB SINAD I believe), and if it does not, that needs to be addressed. Adding in the duplexer, sensitivity should decrease only by the amount of loss previously recorded in the Pass. If the Pass is measured as 'X' and the receiver sensitivity decreases by more-than-'X', than something is amiss at the Circle K and investigation needs to determine the cause. Sometimes it's helpful to take a day off, go poke .45 caliber holes in paper, then come back to it with a fresh mind, starting over at square one. My 2-cents worth. Mike WM4B -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of MILLIN SEE Sent: Tuesday, November 1, 2022 8:09 PM To: [email protected] Subject: Re: [repeater-builder] VHF MTR2000 Poor Receive Performance Sounds like your forcing that duplexer outside it's parameter. Millin ----- Original Message ----- From: Jared Smudde <computerwhiz02@...> To: [email protected] Sent: Tue, 01 Nov 2022 16:55:15 -0600 (MDT) Subject: Re: [repeater-builder] VHF MTR2000 Poor Receive Performance So the transmit side cavities all have 29db-32db of return loss at pass frequency, 30db of notch rejection and 0.4db of IL at the pass frequencies. I went to the receive cavity causing trouble and slid the tuning rod all the way up and cleaned the rod with some fine sandpaper and wiped it down with denatured alcohol. I then took the rod and ran it up and down the cavity several times all while rotating the rod at the same time. I was able to get the return loss to 30DB on the cavity. Probably had to clean some varnish off of the rod and tuning fingers. I reattached the harness and each side had about 1.67db of insertion loss and I was able to get the notch over 105db on each side. I hooked up the repeater and was met with disappointment, repeater is still deaf with no improvement. |
Mike Besemer - WM4B