See correction below in RED. Looks like the Reflector wouldn't pass the EZNEC attachment. I'll have to forward that in separate e-mails - not on the reflector
-----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Charlie Cunningham Sent: Friday, June 07, 2013 4:05 PM To: 'Jim GM'; 'topband'; Tom W8JI Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check Hi, Jim I'm most suspicious regarding your radial systems: * Are your radials resonant? For the purposes that you are attempting, they need to be, in order to maintain the phase relationship between the driven element and the parasite. * Are your radials elevated? * Do your radial systems overlap or pass close to each other?? You can have considerable unintended and competing coupling via the radials that can destroy the parasitic relationship between the driver and parasite. I am attaching and EZNEC file of a 5-element 80m array that I designed and built some years ago, for a friend, Jim, W4RS, when he was in Virginia. It was a wonderful "kick-ass" "knock-'em-dead" antenna for tough long-haul international DX paths and a real "pile-up buster"! If you have access to EZNEC you can have a look. It consists of a central GP with 4 parasites arranged around it in a square. Each of the parasites has a 6 ft shorted line of 450 ohm ladder line at the base. The inductance of the 6 ft shorted line tunes the parasite as a REFLECTOR director. Then the shorted line can be shorted an inch or so from the attach point at the vertical element and the radials, to switch it to director tuning. The result is that in the diagonal directions the array basically operates as vertical 3-element 1/2 yagi. In the N/S/E/W directions it operates as two horizontally stacked 3-element 1/2 yagis that share a common driver. If you have access to EZNEC. Please examine how I handled the resonant radials. The central GP driver has 4 elevated resonant radials that extend outward past the parasites. The parasites each have two resonant elevated radials that are at right angles to one another and are led away from the center of the array to minimize the radial coupling. The result was a "killer" 80m DX array that was the envy of a few serious 80m DXer down here in our area. If you want to play the beam steering, go into the "Transmission Lines" menu in EZNEC and switch them between 6 ft and 0.1 ft. You'll get the idea. The beam can be steered around 8 points of the compass rose. The beamwidth is wide enough to provide complete azimuth coverage at full gain. F/B is excellent! As for 40m, I've never tried that with parasitic GPs. I have built several vertical 40m yagis that employed vertical 1/2 wave elements that were supported by trees or overhead lines for really tough "new ones" with huge hungry pile-ups with excellent results in all cases. (Electromagnetics works -even for us "poor folks"!) The array that I've shared with you should be scalable to 40m. I've done that with EZNEC, but never built it. I don't have any real feel for parasitic arrays with buried radials, or "radials on the ground". I expect that such arrays might require some tricky tuning. BTW - in my experience, with elevated resonant radials, once we have 4 - we seem to be reaching a "point of diminishing returns" and increasing the number of resonant elevated radials doesn't seem to buy much! Anyway, good luck! I would expect that a 2-element 40m parasitic array, that has provision for switching the parasite between reflector and director tuning could be made to play pretty well! If you are 5m from the array, I would think that your measurements are pretty good except for elevation effects. Best regards, Charlie, K4OTV -----Original Message----- From: Topband [mailto:[email protected]] On Behalf Of Jim GM Sent: Friday, June 07, 2013 12:14 PM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check I think your too close to tell, or just coupling into every thing around there. Knowing you I am sure you have done every thing right. Try calling CQ during day light hours and see what signal strengths the Reverse beacons give you. http://www.reversebeacon.net/main.php Problem with doing this is the beacons may not re-spot you until your off the air for say 15 minutes or shift frequency. I do not know how they really tick. -- Jim K9TF All good topband ops know how to put up a beverage at night. _________________ Topband Reflector All good topband ops know how to put up a beverage at night. _________________ Topband Reflector All good topband ops know how to put up a beverage at night. _________________ Topband Reflector
