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ka7niq wrote:
JIMMIE;735930 Wrote: On Mar 6, 12:24*pm, ka7niq wrote:- Cecil Moore;735465 Wrote: On Mar 5, 9:25*am, ka7niq wrote:-- I got to thinking WHY not take a hustler vertical with only ONE *Tuned "radial" for each band ...-- - You are trusting that each radial will be resonant on only one band akin to a fan vertical antenna. What may happen, for instance, is that the 40m radial may accept an appreciable amount of energy on 15m and direct the 15m signal up at a high take-off-angle - less than optimal for 15m operation. Other interactions are possible, e.g. 28MHz/4MHz=7, 18.14MHz/3.6MHz=5, etc. Any vertical radial resonant at 3/4WL, 5/4WL, 7/4WL, etc. will have a suboptimal effect on the take-off-angle. -- 73, Cecil, w5dxp.com- I never considered this Cecil. Would you think it better to use a wire trap dipole instead of the Hustler 4BTV and hang it vertical in the tree ? -- ka7niq- My experience with the Hustler 4BTV hasn't been good. Over two hamfest I bought 4 of them, lucky for me I was only buying then for the tubing and mount and paid around $10 each for them. I dont think any of them had a trap that wasnt bad. Jimmie I have decided against the use of the Hustler 4BTV. I am going to buy a CB antenna for use on 17 through 10 meters, keep the feed line short, and use it with a tuner. I have been reading that several Hams are doing exactly this with the Antron 99 and Sirio Gain Master CB antennas, with decent results. I do plan on a self supporting tower one day, but this will get me on the air, until then. If you put an autotuner at the base of a 1/4 wave 10m vertical (i.e. 2.5m long), and some random length radials, for 10,12,15,17, and 20, it will work fairly well. The feedpoint impedance of a half length antenna (i.e. 1/8 wavelength vertical) isn't so horribly different that losses will bite you. (for comparison.. I ran some models a while ago for a 20-odd foot vertical. resonant (Z=39 ohms) at 9.4 MHz, and at 4.7 MHz, the z was 14-271j. I just happened to have that data handy.. you're looking at a shorter antenna and higher frequencies, but the ratios are likely to be similar. W9CF's tuner calculator says a T network for the first case (Z=39 at 9.4MHz) would have 0.1 dB loss (3%), and for the second case, you'd have 1.7dB loss (33%) While it's not great to burn a third of your power in tuner/feedline losses, on the other hand, it's also not horrible. If you can put up something that's around 3-4 meters (10-13 feet) long, that will work even better. A piece of plastic pipe with some 12gauge wire inside it, for instance. or a 10 foot length of thinwall 1/2" conduit (sure, it's steel, but it's also got pretty good surface area.. without actually doing the calculation, it's probably comparable to a 12AWG wire in resistance) |
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