Hi Guy
Thanks for the reply - most interesting and helpful. I like your conversion idea for the 450' ohm ladder line - like open wire line here too. I did have an 160m inverted-L antenna here with a Moxon-type counterpoise about ten years ago and it was a very useful antenna. However, your counterpoise idea looks like a definite improvement and it would be good to have a choice of polarization here again. Most of my 160m DX has been worked with a cloud-warmer inverted-vee dipole antenna just before sunrise or just after sunset, but the old inverterted L was better on middle distances, particularly out into the Pacific, and there are some countries that I still need out there. I shall have some fun building one of your counterpoises in the New Year (and an inverted-L to go with it)! Vy 73 Steve, VK6VZ _____ From: [email protected] [mailto:[email protected]] On Behalf Of Guy Olinger K2AV Sent: Saturday, 10 December 2011 1:04 AM To: Steve Ireland Cc: [email protected]; [email protected] Subject: Re: Topband: Length of inverted-L antenna for use with K2AV counterpoise Steve, the length of the wire is your choice, with consequences in the tuning realm. The simple solution is to only use the wire on 160, and VARY THE LENGTH of the wire to achieve a minimum SWR or zero reactance at 1.825, or your choice of center of resonance. If the length is fixed (your choice) and the radiator is really short you will need a series inductor, and really long a series capacitor, with a feed Z that depends on the length and configuration of the wire. For the simple solution, neither the series inductor or cap is used, and the length is pruned for resonance, just like a dipole. This resonant length will vary, depending heavily on the environment, type of dirt, just like a dipole. It will also produce a Z that is decent for transmission across 50 ohm coax, and if not close enough to 50 ohms as is, is easily handled by whatever tuner may be in the shack. Obviously we don't have reports from several hundred people who have done this, but the simple solution seems to work out something a little longer than a quarter wave, though it is clear from the small sample so far, that this varies a lot on how one is able to get the wire up. Mine is 3/8 wave, up 90 and out 105, and I use a series vacuum cap to tune it. I also use a 4:1 isolation transformer to up-convert the 90 resonant Z to 360 ohms to match 424 feet of Wireman #554 "450" window line. This is obviously not the "simple" solution. What you do in addition to the isolation transformer and the FCP is just as variable as it ever was. 73, Guy. _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
