Batboard

Problem: Loss of coverage with mobiles and portables

After many years of service my agencies MTR2000 VHF 100W running simplex (FB) operation was converted to a repeater (FB2). Prior to being converted to repeater operation I narrowbanded the site about 4 weeks prior with no change in coverage. The system is using wireline connections to a Zetron console via Verizon RTNA lines.

RX: 151.xxx
TX: 155.xxx

A brand new Telewave 4 cavity duplexer was ordered and tuned from Tessco. A new receive frequency was applied and granted by the FCC. After traveling to the site, which is in a dense antenna farm enviornment approximately 722ft AGL, the antenna relay and external preselector were removed. The system was re-wired to work with the duplexer and tested. The entire MTR including the receiver were given a check on the service monitor and passed with flying colors. Power level checks with a good old Bird watt meter had great results. My problem... The areas once covered by this system in simplex mode are now lost. Some areas suffering poor coverage are only 7 miles away! Other areas with line of sight using a portable 12 stories up are having issues with a clear static free reception by the receiver. During the conversion visit the RSS had the Receiver Preselector grayed out. Should I re-tune the external preselector and add it to the receiver line? Bad duplexer?

Any thoughts?

Thanks in Advance

JJ

You're going to have to check it out. Run the tests. If I had to guess, you have desense on the new rx freq. Not entirely unusual in VHF.

Well the band pass filter coupled with the duplexer did the trick. The receiver was getting hammered with a high noise floor from other stations in the area. I did discover the Motorola Pre-Selector sold with the MTR2000 as an option doesnt do much at all. Maybe 1.5db of isolation at most. Anyone needing better isolation and selectivity should use an external cavity for sure.
JJ

Did you re-tune the preselector? You should get better than 1.5dB out of it. Obviously, if you were issued a new receive frequency, that preselector should have been re-tuned for the new receive frequency.

IIRC there were 2 versions of the MTR 2000 receiver. One that had an on-board, varactor tuned preselector, and one that did not. It's likely the box is greyed out because you have the version that doesn't have the on-board preselector, and instead has the external unit.

And if your RX board does NOT have the on-board preselector, you definitely MUST USE the external one as that's the only tuned front-end circuit the receiver has. It's not necessarily an option unless the RX board has the varactor tuned stages.

The tuning procedure for the external preselector is not intuitive; you're not supposed to just peak it for the best signal, although some people do just that.

Bob M.

Bob, I just received an mtr, looks similar to what your talking about here. Rx module indicates trd 6411 which is no internal. It did at some time have an external that was removed when run as a base station. So to run this in a repeater config without either the internal or external.....impossible??? no rx front end.
Thanks
Gordon