Thanks for asking for details so that you may provide a better answer. First, the site is currently my home at 6300 feet over-looking all of southern California but is not a repeater site. There is a commercial site up the street and one two doors down, but neither currently affects me in the least. A commercial site 2 miles away with a paging transmitter on 152.840 does cause a slight amount of noise, but a PAR Electronics intermod filter does wonders! It has an insertion loss of about .5dB. I just pulled up the 2m machine right next door while listening to .52 and not a bit of notable desense.
The repeater is built using two Vertex VX-4100 commercial radios. They are nice because they have DB15's that bring out the connections. The specs are also excellent. Cabling is with shielded DB9 and DB15 cables into an Arcom RC210. The duplexer is a newly refurbished WA-COM 642 6 cavity Bp/Br duplexer and has a total loss of only 1.38dB. Why then a preamp? Just to recover what I can from the LMR-400 and the cavities. The cable length is so short that hard line isn't justified. My target audience is hand-helds operating in the mountain area that needs to be covered for emergency services. We have major forest fires every year. I will limit my TX power so that I am not blasting areas of little concern off the mountain, but I need hot receive. I am experimenting with a 5dB gain Hustler G6-144b and a 9dB Comet. It is very much proof positive that gain is achieved by narrowing the aperature. Once we determine which antenna works the best we'll go commercial on that. Probably a bi-directional antenna pattern will work the best. As I said, I do have a Decibel DB-4002 cavity but hesitate adding more loss to the system. --- In [email protected], "Joe Burkleo" <joeburk...@...> wrote: > > Bob, > Which preamp you use to work properly in your situation depends on > several details. > > We need a lot more information from you to make any firm > recommendations. There are cases where a lower gain preamp will > actually produce more measurable results. If for example the site has > a higher than normal noise floor a lower gain preamp will often times > amplify more of the signal and less of the extra site noise, where a > higher gain preamp may amplify both the noise and signal, giving you a > signal with more noise than you would like. > > The choice of preamp also depends on what equipment you are using and > what the power level of the transmitter is, and what type of cabling > is used for intercabling within the repeater, and also what type of > feedline to the antenna you are using. > > In general on a site with a high noise level I prefer to use Angle > Linear preamps, or if you are using a Micor or Mastr II repeaters, the > factory preamps can be a help as they are only about 10 db gain. > > As was mentioned, a pass cavity (the deeper the skirts the better), > after the duplexer in front of the preamp, is a must, especially on a > noisy site. > > If you can give us a little more information, some of us can get you a > little closer to where you want to be. > > From my past experience with them, I would not use a Ham-Tronics > preamp on a noisy commercial site. > > Joe - WA7JAW > > [email protected], "Bob Ricci" <bob@> wrote: > > > > Hamtronics has a preamp with a helical resonator with a 18dB preamp. I > > am at a high elevation with noise all around me. Advanced R3esearch has > > a 24dB preamp with a low NF and 1dB compression point. Either would be > > behind a WACOM 642 6 cavity duplxer. > > > > Which would be the better approach? The ultimate goal is to improve > > reception of handhelds in a mountainous region. > > >
