At 2/4/2009 13:08, you 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.
Neither. I recommend an Angle Linear preamp (http://www.anglelinear.com) with a cavity filter ahead of it. Angle linear has those too, but you can probably find a surplus cavity for much cheaper at a hamfest or eBay. Helical resonators are either lossy or don't offer much out-of-band rejection. They are really best suited for space-constrained installations. Full 1/4 wave or 3/4 wave cavity filters are large in comparison but offer high Q with minimal passband loss. Bob NO6B
