|Subject:||Re: [TowerTalk] Shields|
|Date:||Wed, 13 Oct 2004 23:33:51 +0000|
Actually, in my experience using hardline or 100% (or at least very good double) shielded cables in VHF-UHF repeater systems and cavity interconnects in duplexers does make a difference, not necessarily in notch depth but in generated noise that can bother receivers. I also see this "noise" issue when using many antenna designs that are perfect for simplex operation and stink in duplex operation with any power applied. It seems the oxidation between shield strands, which is always there even with brand new cable and worsens with age, creates minute noise-generating interfaces (or something). I've put up repeaters using brand new mil-spec RG213/U and running 100W output power with a very good duplexer had desense problems resulting in poor receiver performance. Replacing absolutely nothing in the system except the transmission line, going from 213 to 9913 or hardline or some other 100% shielded cable, completely eliminates the noise -- it's gone. This has happened to me so many times it cannot be coincidence.
<snip bit on clamped vs welded antenna construction>
With all the energy floating around hilltops, any diode action anywhere is bound to bring grief. Certainly sounds like the mechanism here & going to better shielded cable might have simply gotten rid of a bunch of diodes & not really improved things because of the greater amount of shielding.
Ditto for the antennas. I can just imagine what sort of nasty joints there are on some of our repeater antennas here, as it has been hard to spend the money on the better ones & everything lives in a very moist, salty & dirty atmosphere that eats into just about anything in short order.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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