Below...
> On Thursday, Mar 8, 2012, at Thursday, 12:14 PM, Gary Hinson wrote: > > > ... and thank YOU Jim for your encouraging words. I do have the space > for > > several quadrillion radials but not the energy to cut them all into the > > ground below sheep/cattle/deer foot level. So I'm waiting for the > postman > > to deliver some cores from Amidon, and I'll give an FCP a go. > > > > One thing is not v clear on W0UCE's site is the antenna: he shows an > > inverted L coupled directly in - it looks v simple but my inv-L will be > > different so aside from trimming the length and maybe configuration of > the > > L, are there any other tricks to achieving system resonance? I have > tall > > fir trees to hang the antenna from, so mine will be close to a quarter > wave > > vertical I hope. > > > > 73 > > Gary ZL2iFB www.G4iFB.com Hopefully a short simple addition to the discussion. Jim is using the 80m version of the "simple" arrangement: FCP plus required isolation transformer (IsoT) plus quarter-wave-ish radiator that is pruned to center the best impedance range at the desired operating frequency, and has the mechanical simplicity of a balun in the middle of an inverted vee. The FCP, being 5/16 on its only band (not multiband) is quite capacitively reactive. The IsoT has quite a bit of leftover inductive reactance on its band. The parts in the IsoT were chosen for efficiency, and in addition, under the antenna load, to have an inductive reactance that is close to the FCP, with the opposite sign. The turns count on both the 160 and 80m versions are specifically picked to allow you to put up a close-to-quarter-wave radiator that can be pruned to a zero reactance and an R in the 50-ish range as seen ON THE SHACK SIDE of the IsoT. Most are putting up inverted L's as radiators, for residential-plot-specific reasons, where trees are, etc. But you can put up any radiator you want. The different X and R curves for various "typical" 1/4 wave inverted L's and other radiators mean that sometimes you may have to start adding things to the IsoT to tune R and X. This gets into understanding tuning networks. There are some remarkably useful complex configurations using IsoT's and FCP's, but you won't work them just reading SWR, and you'll need to be looking at them as complex LCR networks. If you put the behavior of the IsoT under load into a model, you have to use an LC network plus a transformer widget to describe it. So in truth the antenna per se -- the 1/4-wave-ish radiator over the FCP -- is NOT a resonant antenna. You are using a required isolation device with INDUCTIVE non-resonant network characteristics that have been picked to be the opposite of typical L-wire/FCP CAPACITIVE non-resonant characteristics. For many, just pruning the L gets it close enough. Others have lengthened the L to make it inductive and put a transmitting cap in series. The details are at http://www.w0uce.net/K2AVantennas.html 73, Guy. ______________________________________________________________ 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
