Oh, I agree that it works acceptably well right out of the box, and I've made contacts with it. I've also noticed little to no difference changing the polarization by rotating it. I wonder if the proximity to the ground, and the person holding it, is why the polarization doesn't seem to matter too much. I know for a fact that polarization *does* matter if you're using a Yagi up on a tower. I get better signal strength from my omni on 2 meters than from my 9-element horizontally polarized M2 Yagi when pointed at the same repeater. And at a previous job, one of my responsibilities was to aim satellite antennas, and "peak and cross-pole" them. I've seen well over 20dB difference from being on the "wrong" polarization. Theoretically, it's infinite, but due to how the feeds are made, and other factors, it's never "infinite". As for Al's software program being "wrong", it might not be the software, but how it was used. I'm not knocking Al; he's provided a great, unique product for the Amateur community. If I were better versed in the use of antenna-modeling programs, I'd measure out the antenna and check it for myself, but I'm not, so I go by what other antenna experts that I respect have said. I suppose an easy way to get a rough idea on this would be to see where the SWR is lowest in the 70cm band. My antenna analyzer doesn't go that high in frequency, so I can't do that. Britain's article was in the Summer 2006 issue of "CQ VHF", where he states that the antenna has been measured at several conferences, and has showed gains of around 4dBi at 435MHz, well short of what 7 elements should give. For example, an M2 6-element, end-mounted 70cm antenna is rated at 11dBi, and a Gulf Alpha 8-element, end-mounted 70cm is rated at 13dBi. His NEC evaluation based on the element length and spacing showed forward gain *should* peak at around 457 MHz, and that his NEC model suggested the boom correction factor for insulated vs directly mounted elements was not applied, and that the elements appeared to be about 1/2" short. And as the Arrow Antenna website states, "This Antenna has not been tested for gain. No need, it works." Can't argue with that! For the small cost of a box of 1/4" threaded spacers, I think it's worth making the elements longer. Jim KQ6EA --- On Sun, 8/16/09, Clint Bradford <[email protected]> wrote:
From: Clint Bradford <[email protected]> Subject: [amsat-bb] Re: Arrow Antennas To: [email protected], [email protected] Date: Sunday, August 16, 2009, 1:19 PM > ... Why are we modifying the Arrow? > ... Because someone's analysis says the element length is all wrong ... So Al Lowe's software program which he used to design these is all wrong? Sorry to get defensive on Al's behalf. This thread just "feels" like a re-hash of an "engineer's view vs. real world results" argument. Like when I was told here - by engineers - that it mattered how I twisted my Arrow while working the sats. "Ya gotta take polarization into account, Clint - there's a 22db difference when you turn your antenna 90 degrees - a tremendous performance hit if you don't take this into account ... " Yet in the real world of demonstrating workin' the birds, there's no such performance degradation. I have hundreds of witnesses to this fact: Capture SO-50 and AO-51 with the Arrow and operate TX and RX while twisting the antenna in different angles doesn't change the great reception and transmission quality. If you are in the market for an Arrow, I simply suggest that you use it as offered to you. You will be pleased with its 2M and 440 amateur bands performance. And leave the modding of the elements w-a-y on the bottom of your "things to do" lists. Clint Bradford ---------------------------------- Clint Bradford, K6LCS http://www.clintbradford.com _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
