Hi Fred, Loss *anywhere* would broaden the antenna. Famously the B&W folded dipole, fed at the center of one wire, and terminated with an RF resistor at the center of the other, has for decades been serving commercial installations with widely separated operating frequencies not connected by any fortunate harmonic relationship. That antenna has roughly an intentional 3 dB loss at a designed position in the antenna. See https://www.bwantennas.com/images/fdipole.gif for a drawing.
In the case of your EFHW, the broadening loss is the dielectric loss in the fence itself, and in the ground very close underneath. The B&W folded dipole as a solution sticks in the craw of a lot of hams, because we always think there is some way to navigate the problems and keep the 3 dB for ourselves. The thought of heating up the air with half the power out from out two kilo-buck brick-on-key PileUpBuster brand amp just bothers us no end. And where the power to the antenna cannot be increased by 3 dB to compensate, if we regularly work the barely open paths on the low bands for new DX and contest multipliers, that 3 dB can make a huge difference. BUT... If we are just dodging the HOA, vs creating a remote site, or not operating at all, what you describe seems quite reasonable. One half wave on 80, two on 40, three on 30m, four on 20m, etc. allow a rather simple feed mechanism, and any sloppiness will be mitigated to some degree in the unavoidable dielectric loss of the fence and ground. In the past, particularly with tetrode final tube(s), a pi network would absorb ugly antenna impedances just by load and tune, easily servicing impedances that would croak transistor amps. Back in 1959 I regularly worked the traffic nets end-feeding 120 feet of wandering wire up about 20 feet against a ground pipe, fed with about 30 feet of coax directly from an 807 tetrode and a pi network. I was not loud, but I won a BPL medallion. A later addition of a home brew 250TH amp improved things quite a bit for the folks on the other end, but the antenna was as much as I could ever do from that location. 73, Guy K2AV On Thu, Aug 4, 2016 at 6:22 PM, Fred Jensen <k6...@foothill.net> wrote: > Ummm ... my HP48GX says 102' is very very close to 3 half-waves at 14 MHz > which sounds sort of resonant-ish. Maybe a little known bug in my > calculator? > > On a similar path, I decided to try out the 80-10 EFHW from MyAntennas as > an HOA Stealth antenna strung along the top of a 6' fence. It's 130' long, > has a 6 turn series inductor wound on a Sch 40 PVC fitting a short distance > out from a heavy-ish box with an SO-239. I figured there might be a 50 ohm > resistor in the box a la the famous B&W folded dipole that graces many > National Guard Armories. > > The impedance sweep when I got it yielded close enough to 50+j0 ohms on > all bands ... except 60 m that my K3/100 is happy without the KAT3. It > also revealed nearly infinite impedance between the bands, sort of ruling > out the resistor [I've come to believe it's a transformer, maybe of the > "auto" variety]. > > It works surprisingly well. On 80 and 40 it's pretty NVIS, which happens > to be what I'm looking for. Above 40, the pattern starts to become more > complex and much less vertical if I can believe EZNEC. 6' AGL is obviously > not optimal ... except for our HOA and the CC&R's ... but I'm very > surprised at how well it does, especially at the bottom of the cycle. > > This list seems to have a number of antenna experts aboard [and maybe a > few who play antenna experts on TV] ... would anyone like to 'splain to me > how it achieves low SWR on all bands? I could probably ferret that out > with enough time, but if someone already knows ... > > 73, > > Fred K6DGW > Sparks NV > Washoe County DM09dn > > On 8/4/2016 1:41 PM, Wes Stewart wrote: > > It's a pity that too many newcomers, as well as many oldsters, are >> enamored by this piece of wire. First, a 102' length is not resonant on >> 20-meters, so in common jargon, it's *n >> > ______________________________________________________________ > 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 > Message delivered to k2av....@gmail.com > ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
