KL7MJ wrote: ↑Fri Sep 08, 2023 12:30 am
Nice work Andrew!
I'm beginning to think that an EFRW is a great general purpose antenna, so long as you have a tuner. I have a 35.5/17 EFRW that does very well for me, but I think that the longer the antenna and radiator, the better.
My current antenna project is a travel EFRW using a pair of slinkies, with a 9:1 balun. It may not be great, but I hoping it will be good for use in a hotel room.
73,
Mike, KL7MJ
Hi Mike, thank you !
As for the EFRW, its main advantages imHo are the ease of installation, the coverage of all bands, the fact that even if shorter than a dipole/doublet it may still be used on lower frequencies (with reduced efficiency btw) and then, it's almost "stealth"; on the other hand the EFRW is, as many other antennas a compromise, so we should accept some limitation, but I think we may live with that
As for the tuner,, willing to spare some money, one may just build it, in such a case I suggest to look at this one
https://pa0fri.home.xs4all.nl/ATU/FRIma ... tcheng.htm
and in particular, at the schematic of the DL4CS version found further down the page, it doesn't go down to 160m but since it doesn't need a "band switch" it's easyy to build, compact and can be easily turned into a remote ATU just by using a pair of stepper motors

in such a case, the EFRW could be fed directly from the ATU (installed at the antenna) w/o using a 9:1
As for the length, longer isn't always better, set aside the losses due to wire resistance, we should consider that, at higher frequencies, where the radiator size may be several wavelengths, the antenna will become more and more directional toward its endpoint (which may be desirable or not), plus a very long antenna will present mechanical issues making the setup more complex, my usual "go to" to pick an EFRW lenght is this one
https://udel.edu/~mm/ham/randomWire/
and I believe that 203ft is the limit for an EFRW, and then we should consider how we'll be going to install it, a good way (example with a 137ft radiator) is placing the feedpoint at (say) 6ft from ground, going up to about 33ft (or more) and from there sloping down to about 17ft, the resulting "inverted L" setup will give pretty good radiation pattern
As for the "slinky", that's made of steel, so its radiation efficiency will be much lower than copper, not that it won't work, but we'd probaly loose quite some of our precious W as heath
