On Sun,3/19/2017 7:25 PM, Steve Lott wrote:
Ed and Jim
I am also building an 80m Rhombic on the back 24 acres of property
progress is slow, it won't be high but hopefully it will be an asset in
ARRL SS from North Texas
If you're on the west coast or KH6/KL7, a gain antenna pointed east is
an asset for SS. If you're in the middle of the country, it's a
liability, and a dipole is better.
at least one person has told me the Rhombic is a waste of my time and I
should just use Inverted Vee's at 60 feet of height
I agree that a Rhombic is a pretty limited antenna on 80M. Instead, I
would consider a flat dipole as high as you can possibly get it,
spending the bucks needed for those poles for tall towers instead. Take
a look at http://k9yc.com/AntennaPlanning.pdf which shows the value
in dB of height of horizontal antennas. My 80M antennas are dipoles at
140 ft (I have redwoods), and the one broadside to the NE has a
reflector giving it gain to EU and the east coast. My ground
conductivity is pretty bad, so the only band where verticals outperform
dipoles is 160M -- even at 140 ft, a horizontal antenna is low on 160.
:) I had one for a while, and with a LOT of A/B comparisons the
vertical nearly always beat it.
I have the Telephones poles installed now just need to find the time to get
the wire strung tune it and run a thousand feet of ladder line to the back 24
acre lot from the Shack
I currently have One Four Square installed for 40m
it is on The Eastern side of the property and Northern Half
I plan on the 80m Four square Due west of the 40m array
with a separation of 600 feet
As that Antenna Planning link clearly shows, the gain of a vertically
polarized antenna is strongly dependent on the quality of the soil, both
under the antenna and in the far field. A 4-square will have significant
gain over a single vertical installed at the same spot, but if you have
poor ground conductivity, a high dipole may outperform it, because
horizontal antennas are NOT affected by ground quality, they are
affected only by their height and the terrain.
The only other Current antenna in use for Transmit is an Eight element
Sterba Curtain Array
hung with broadsides to NE and SW hung between two, not quite high enough
telephone poles.
Bottom edge of the array would touch the ground but is propped up on
insulated posts
It seems to work rather well on 20m, but right now I have little to compare
it with
Have you modeled it? I suspect that those very low elements are
worm-warmers, burning the part of transmitter power fed to them.
Ed,
You mention 1/2 inch cable TV hardline and I have a spool of that but have
not seriously planned for it's use
did you do anything to reduce the impedance mismatch from 52 ohm line
I know it's not a lot of mis match, so maybe you just don't worry about it ?
I use that stuff to feed monobanders for 20 and 15. The hard line is
carefully cut to multiples of a half wave, which approximately makes
them disappear from a mismatch point of view (the approximation is their
loss). See k9yc.com/Coax-Stubs.pdf
I further optimize it by measuring the feedpoint Z of each antenna,
importing that in SimSmith, and tweaking the length of the 50 ohm
section between the antenna and the 75 ohm section to optimize the match
over the band. In at least one of those antennas, I used a stub in the
50 ohm section. See http://k9yc.com/PacificonSmithChart.pdf for the
general technique.
You'll need a good way to measure antenna impedance. I strongly
recommend the VNWA 3e, designed by EE prof DG8SAQ, built and sold by SDR
Kits in the UK. Excellent bang for the buck, especially with Britain's
Brexit mess, far superior to other products from US mfrs.
http://sdr-kits.net/VNWA3_Description.html
73, Jim K9YC
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