If you are talking about multi-band operation, you can expect the SWR to range up to above 60:1 on some bands, particularly where the radiator is near 1/2 wavelength. That's why ATU's designed for operation at the antenna are used for such applications. And, yes, they tend to be expensive.
The Stepper antenna adjusts its length to 1/4 wave on the band in use, AFAIK. That way it presents a decent match to coax on any band in its range. However, matching to a longer antenna up to 5/8 wave provides substantial low-angle gain over a 1/4 wave radiator. That's easily done with a matching network at the base. One way to accomplish that at a lower price than a commercial ATU at the antenna is to put in a matching network for each band, relay switched, at the base. On some bands only an inductor will be needed, with taps for each band selected by relays if you are adverse to going out to the antenna. On others capacitors may be involved (such as when the antenna is near 1/2 wave long and presents a very high impedance at the base). IN that case you might have a separate network that is switched in. It's not as "hammer simple" as buying an ATU and plugging it in, but it can be even more efficient and at a lot lower cost. For many of us, that's what makes Ham radio fun: doing for $1 what anyone with a fat wallet can do for $100. You can probably get away with one matching network setup per band, at least on 40 and up, and keep as low an SWR to the actual rig as you want using the rig's built in ATU. (That's what it is really for ;-) Just be sure the SWR on the coax isn't so high you have unacceptable losses. With an insulated pole like you have, another way to economically arrange a vertical covering several bands is to tape several radiators to it, insulated from each other, each 1/4 wave long for the band of interest. You can feed them in parallel with one run of coax, especially when dealing with harmonically-related bands (e.g. 40/20/10 meters) but it can be made to work on other combinations with a little pruning so that the SWR is low enough to avoid excessive coax losses. Then you let your rig's ATU do the final tweaking to keep your finals happy. You might do a little research on radials. The relationship of the number of radials to antenna efficiency is not linear. The more radials you have, the less adding more improves the efficiency. Also, the higher the feed point impedance, the less important near-field ground losses become. For example, a half wave radiator with a feed point impedance typically several thousand ohms is very efficient with no ground connection at all. OTOH a 1/8 or 1/16 wave radiator with a feedpoint impedance of less than an ohm requires the best possible ground for any reasonable efficiency. Ron AC7AC -----Original Message----- Recent discussion regarding verticals, internal antenna tuners and remote antenna tuners was very interesting. Based on that discussion, it seemed the "optimized" solution was a vertical, with good radials, and a remote tuner at the base (generalization). In the near term I want to try out (experiment with) a 33' vertical. At Frostfest this year I picked up 32' or so of fiberglass mast. I am going to tape a wire to this that is 34' long, twist the mast to wrap the slack up, much like a widely spaced helical. When setup at home, it would (eventually) have a good ground field (would start out with 16 radials and work my way up to 60'ish). The coax run when used at the house would be less than 40'. When setup for portable operation (connected to mount I have for my trailer hitch, to use when parked) it would have 4 radials of a length not yet determined and the coax run would be less than 20'. In both cases I would be using the tuner for the K2 (portable) or K3 (at home). In the long term, I am thinking about the SteppIR vertical (haven't decided which one). Same deal with the radials. It would inherit what I had down, or start at 16 and work up. http://www.steppir.com/files/vertical%20brochure.pdf Current plans are for ground mounting. I understand that as radials go, more is better. The radials would be black insulated wire on, or within 1" of the surface of the ground. They would not be cut to 33' or less if the space was not available. I am curious on the experience of the group with a similar vertical, tuner at the rig, and short coax run. I am also curious of the experience of the group with the SteppIR verticals. There is similar up front cost as the vertical / remote tuner solution (assuming a new weather proof tuner). Thanks for the always enlightening discussions. 73 Dave Wilburn NM4M ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
