----- Original Message ----- From: "Rick Karlquist" <rich...@karlquist.com> To: "W0UCE" <w0...@nc.rr.com> Cc: <topband@contesting.com>; <cw...@yahoogroups.com> Sent: Thursday, December 08, 2011 9:41 PM Subject: Re: Topband: K2AV 160m Folded Counterpoise Antenna - New Details Posted
> W0UCE wrote: > >> * The ONLY means of achieving the required degree of Isolation is to >> use the Isolation Transformer as specified by K2AV >> * Tests using 1:1 Baluns and Line Isolators have ALL FAILED - you >> waste RF Power, Time and Money unless the specified xfmr is installed >> * DO NOT attempt to use Insulated Window Line for the FCP - We already >> tried it and it does not work - too lossy >> * Use #12 Bare wire for the FCP elements - Moisture gathers on >> insulated wire and detunes the FCP > > I haven't built this system, but the suggestions above make sense. > I have been trying to encourage using transformers instead of baluns > on 160 meters for years, but it's a tough sell to overcome the balun > habit. The tendency for loss in the open wire line also makes > sense. It is well known that window line is lossy when wet. > What is new here is that the Q is so high that you can't even > use insulated wire for open wire line. It would be interesting > to see if teflon insulated wire worked OK. The electric field > is maximum right at the conductor surface, so the insulation has > a considerable effect on characteristic impedance, thus I could > imagine it would affect loss too. I am feeding my vertical > using 850 feet of open wire line with XHHW insulation (whatever > that is made out of). It would be interesting to measure the > loss on a rainy day and see how much it increased. It's only > a few tenths of a dB when dry (the wires are 4 AWG aluminum). > > Rick N6RK Using a 120VAC 60Hz source and a 10A load the loss in 850' of #4 copper is 5.1V or 4.2% With aluminum it is 7.3V and 6.1%. It only gets worse at RF and once you reach about 3dB loss the input VSWR flattens out until it appears to equal the line impedance. Ground losses in a vertical have the same effect. Adding a pad between the signal source and DUT in the lab is the standard procedure to eliminate a matching problem. Carl KM1H _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK