Hi all,
For many years I’ve had a trapped 80m/160m inverted vee with the apex
at about 94’ on a tower that’s loaded with various yagis. The vee is
oriented so that it’s broadside to the NE and SW (wires running SE to
NW). The tower is on a steep hill, so the wire that runs to the uphill
side is only about
17 feet off the ground, while the wire on the downhill side is about
27 feet off the ground (maybe more).
The traps are Rayco KW-80C, which is cut for 3.625 MHz, setup for
two-band operation. On each side, the 80m portion above the trap is
cut to 68 feet and the portion below the trap is cut to ~47’, for an
overall length of ~115 feet per leg.
As you would expect, the bandwidth on both bands is narrow. Since I
operate almost exclusively on CW, and have an 80m delta loop with
better radiation angle and bandwidth, I only use the 80m portion of
the trapped vee for an SDR that monitors the band (due to switching
limitations, the SDR can’t use the delta loop).
The lower wires have been trimmed to center the antenna at 1.830 MHz
on 160m. The 2:1 bandwidth is about 40 KHz, and around 70 KHz between
the 3:1 marks. So the antenna is useful on most of the CW portion of
the band. It hears OK when the atmosphere is quiet, but normally I use a 520’
dual-direction NE-SW beverage for listening. As expected, the
effectiveness of the transmit portion is limited. I’ve worked at least
100 countries with it, and in a typical contest I can work EU and
SA/Caribbean if conditions are good. But I’m usually well behind the
top stations in multipliers – maybe a little better than half what they have.
Again, no surprise.
Recently I started thinking that maybe I should ditch the traps and
convert the antenna to a full-size 160m inverted vee. The overall
length and height of the ends above ground will be comparable. But
when I compared the 160m inverted vee to the 80m/160m trapped inverted
vee in EZNEC+, there was only marginal difference. They’re both cloud
warmers at DX angles, and the SWR bandwidths were the same. I found
this somewhat surprising, given trap losses and such. I would have
expected a more noticeable difference in gain, angle and especially
bandwidth. So, my first question is, am I reading the
EZNEC+ results right, and there’s no real advantage to converting the
antenna, especially in light of losing it for SDR use on 80m?
Second question came up while I was reading some articles about 160m
antennas and came across one that said more radiation comes off the
wires of an inverted vee than broadside. I was under the impression
that inverted vees are omnidirectional, and if there was any
directivity it would be broadside, like a dipole. I happened to orient
my trapped inv vee so it’s broadside to EU (NE/SW) on the tiny chance
there could be some directivity in that direction. But if the article
is right, or if the radiation is truly omnidirectional, then I’m
better off orienting the legs NE/SW (broadside
NW/SE) because the slope of the land would allow for the uphill leg to
be considerably higher off the ground (it would run mostly over flat
ground), though it’s not clear to me what advantage that might confer.
However, there’s a more definite advantage because the legs of the
inverted vee would be much farther away from my beverage. Right now,
one leg comes within about
20 feet of it. If I reorient the antenna it would be over 100 feet away.
Comments?
Finally, another option would be to ditch the traps and one leg, and
slope the other leg towards EU as a ¼-wave vertical on 160m (with lots
of ground-mounted radials, of course.) Unfortunately, that would have
to be the uphill leg, so the vertical would be somewhat flatter than
if I could point it SW. Would such a vertical be superior to what I
have now or the dedicated inverted vee?
73, Dick WC1M
_________________
Topband Reflector Archives - http://www.contesting.com/_topband