On Mon,7/18/2016 12:25 AM, rick@dj0ip.de wrote:
Roger, then let's stay with resonant antennas.
The feedpoint impedance is not only dependant on the impedance of the antenna
but also on the transformation of impedance due to the specific length of
feedline . . . which varies from one band to another.
Rick,
You miss the point. In general, multiband antennas are NOT resonant, and
they do NOT match the feedline within reasonable ratios. That's Gary's
point, and it's mine as well. There are lots of ways to make a single
antenna resonate on multiple bands. Fan dipoles, trap dipoles, even some
loaded dipole designs, and combinations of fans and loaded dipoles.
Barry at Hypower Antenna Co (it's a basement enterprise, I never
remember his call, but a good guy) sells a loaded dipole for 80 that is
also resonant on 40, and to which a 20M fan element can easily be added.
I've very successfully used a 160/80/40 version of that design at
several QTHs. See my website for construction details on fan dipoles,
buy the coils from Barry. Loaded antennas in general are not very
broadband, so you'll need a tuner. Also, in a fan dipole, the higher
frequency element has about half the SWR bandwidth of a non-fan dipole,
but 40M is not a very wide band, and neither is 20M (thinking percentage
bandwidth, which is what matters).
I've VERY successfully used 20/15/10 fan dipoles, both in Chicago (only
30 ft high) and here in W6 (100 ft or so) before I had a SteppIR.
Also, consider this -- we're on the downside of the solar cycle, 10M is
a lot less open, 15M not a lot better. It was a down part of the cycle
when I moved to W6, and I lived 3 years in W6 before I made a Q on 10M
beyond single hop Sporadic E, and nearly that long on 15M. You guys in
EU can work another country single-hop Sporadic-E on 10M, but here in
W6, we need the F-layer to work anything but K, VE and XE. :)
73, Jim K9YC
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