Hi Jim
The omission of the words ‘inverted vee’ in front of ‘dipole’ for Tom W8JI’s
antenna up 300 feet high was a slip of the keyboard at my end! I used to work
Tom regularly back when he had the antenna up and helped him with comparative
signal reports.
When he was doing signal comparisons, Tom never used to name the particular
antenna he was using at any one time, so as to remove the possibility of any
psychological bias that might occur if the station he was working happened to
favour a particular type of antenna. Each antenna Tom used was only referred
to as ‘Antenna 1’ or ‘Antenna 2’ and he told me he also used to switch the
designations around.
As you say, an inverted-vee dipole is definitely inferior to a flat-top dipole.
From memory, I recall John ON4UN found by modelling that a 90 degree inverted
vee in the broadside direction was around 1 to 1.5dB down on a flat top dipole
at the same height as the inverted vee’s apex – and the radiation angle of the
latter was slightly higher, owing to average height of the latter being less.
While 1 to 1.5dB might not mean much on the upper bands, on noisy 160m it might
make the difference in being above (or below) the noise at a DX station.
All that being said, my main point was that a combination of latitude
(reasonable high) and low soil conductivity in south-west VK6 mean that the
losses of predominantly vertically polarised antennas are such that a
predominantly horizontally-polarised antenna is better. My present
inverted-vee dipole has its apex at 90 feet, but I’d swap it like a shot for a
flat-top at 90’ if the yard-size here allowed.
Vy 73
Steve, VK6VZ (also G3ZZD and VY2LF)
## W8JI never had a dipole up 300 ft. He had an inverted VEE up 300
ft. I believe the enclosed angle was far less than 90 degrees.
You require 2 x 300 ft towers to string up a 160m dipole at a height of 300
ft. W8JI only had 1 x 300 ft tower at the time.
Tom, N6BT is adamant that a rotary dipole will outperform an inverted vee
by 6 db, with the apex of the Vee at the same height as the rotary dipole.
N6BT also claimed the rotary dipole would have a 14 db FS.... on DX signals.
## Years ago, I heard these 2 fellows on from Oregon. One of them had up his
new F12 160m rotary dipole, mounted on top of his 120 ft tower.
This 160m rotary dipole was aprx 102 ft long, and used LL wires both
above..and below the main trunk section. The fellow was using a MFJ-259
at the time, and those things wont work below 1800 khz. The rotary dipole
was resonant below 1800 khz. They finally got it sorted out..and resonated
it
at the low end of 160m band. 2:1 SWR BW was aprx 18 khz. IE: + /- 9
khz.. Relays have to be used to switch band segments about.
The very 1st DX station he worked was a 4X4 on CW..... go figure. Trying
to work EU from the west coast on 160M is a tough nut to crack.
## If using an inverted vee..and say oriented N-S..... then move the legs so
they are now E-W, I never saw any difference, minor at best, but that was on
80m,
and also 40m..... and in both cases, the re-orientation of the legs was done
fairly quickly. I believe the baluns I used at the time were flaky at best...
BN-86 junk.
## Other than the fellow in ORE, I never heard about anybody else using a
loaded rotary dipole on 160m. I have heard several rotary dipoles on both 80m
and also 40m.
The 80m rotary dipoles that I have heard on the air had pretty substantial
signals if oriented broadside in my direction. When the bands were lousy, and
signals were weak, the
fellows with the 80m rotary dipoles were way ahead of the fellows with the
inverted vees. I never did find out what the RX noise level was like with
the 160m rotary dipole
in Ore.
Jim VE7RF
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|