On Mon,12/12/2016 5:32 AM, Catherine James wrote:
I hear a lot of recommendations here for antennas that are flat across the band
and very close to SWR of 1:1 to keep solid-state amps happy. That is
completely unrealistic on the low bands.
I have to re-tune my 160 meter dipole for even small excursions of a few tens
of kHz. A cage dipole would be broader-banded, but that is difficult to build
and install, especially for a 270 foot long antenna that hangs in the trees. I
certainly couldn't put one up in the treetops where my current wire dipole
lives, as it would get all tangled in the branches.
Excellent post, Catherine. You have hit the nail squarely on the head.
However -- even a dipole at 100 ft is "low" for 160M, so it's both
inefficient and radiates more at high angles than low.
A FAR better choice for something suspended between trees is a Tee
vertical, where a flat top wire provides top loading for the vertical
section, which does the radiation. Because antenna current splits
equally left and right into the top wires, radiation from the top
cancels, and you end up with a nice vertical radiator and a nice low
angle of radiation. My primary TX antenna for 160 is a Tee vertical hung
between trees, and I've broadbanded it by making the vertical section
two #10 wires spaced by about a foot. This approximately doubled the SWR
bandwidth.
Any end fed wire needs a counterpoise, either in the form of radials or
some wire to carry the return current. If you don't have room for a
radial system, K2AV's "Folded Counterpoise" is a very good alternative.
Lots of ideas about 160M antennas in these slides for a talk I've given
at Pacificon and to several ham clubs. http://k9yc.com/160MPacificon.pdf
AND -- there's another point that virtually EVERYONE who has commented
in this thread seem ignorant of. ANY distortion mechanism produces BOTH
harmonics and INTERMOD. On SSB, it shows up as splatter, and on CW it
shows up as clicks (remember that CW is 100% AM of a carrier by a
rectangular wave, and the rise and fall of ANY rectangular wave consists
of an infinite number of harmonics that excite IM.
An RF amplifier that is poorly matched to its load creates a lot more
distortion. Yes, we can filter the harmonics, but we can't filter the
IM. This is NOT a matter of making the load EQUAL to the source
impedance, but rather of providing to the output devices, solid or
hollow state, the load into which they work most efficiently and are
most linear. I'm sure that most readers of this list are old enough to
remember load lines. :)
So much of discussion and recommendation around antennas seems to unconsciously assume
that we are talking about the high bands. I've lost count of the number of discussions
where someone asked for a reco on an HF amp, and was told over and over, "don't
start with an amp, improve your antenna system, put up a beam, etc."
At this point in the cycle, I am spending more and more time on 160, less on 20
and 40, and essentially none at all on 10 and 15. Few hams can put up a beam on
the bands below 20. The longer the wavelength, the wider a given band will be
as a fraction of that wavelength, and the less broad-banded the antenna will be
without tuning. Tuning is a fact of life, and amps are more important on bands
where the ham cannot have a rotatable directional antenna.
Again, exactly right. I have high fan dipoles for 80 and 40 (two at
right angles to each other), and have switched stub matching networks
for the CW and SSB bands.
160 has been amazing lately.
Yes, it has, although what you can work depends a LOT on where you live.
Those near the Atlantic get nice openings to EU over an all water path.
From the west coast (I'm near San Francisco) we must go over the polar
path. I haven't even HEARD EU in three years, and I have a 550 ft
Beverage aimed to EU. :) OTOH, I've been monitoring the JT65/JT9
frequencies (USB, suppressed carrier frequency of 1838 kHz) for a couple
of weeks, letting the decoder run all night. In about 3 weeks, I've
decoded signals from more than 400 different stations, many from east of
Chicago, a few from EU, VK, and BA.
10 doesn't appear to have opened at all for the contest last weekend, at
least not here in New England.
That depends entirely on when you were in the shack. I worked 44 states
with 1500W and a 3-el SteppIR. The only states I missed were DE (N3DXX
was active, but not in the few hours the double-hop sporadic-E path was
open between us), WY, MO, IA, NE, SD, and ND. I also missed the VE
provinces east of VE3 and NT. I chose to only work CW. I also worked
20 countries, but no EU, AS, or AF. DX was double-hop to the Caribbean
and trans-equatorial to SA and OC.
And 160 is where you really, really want an amp!
Yes. But having done WAS on 160M in a weekend contest, first with legal
limit, then with 100W, I now need only VT and SC to finish it QRP.
I've been at that for four years.
73, Jim K9YC
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