Hmmm. Interesting theory Vic. I agree that ambient noise probably
doesn't have any particular polarization. My dipoles clearly have less
noise pickup than my verticals. I do have a Cushcraft MV-6 compact
vertical on top of the garage which has a balun as part of its design
and it's noise level seems lower than the ground mounted verticals.
But, it also has negative gain compared to a dipole or a full-size vertical.
I was planning an experiment consisting of a full size vertical radiator
made of aluminum tubing and two horizontal ground planes made of
carefully tuned ham sticks. Now, I'll be sure to feed it through a good
current balun to insure the feedline is fully decoupled.
Another experiment on the summer agenda is a full-wave loop configured
as a vertical rectangle to produce a 50 ohm feed point. I've read that a
full wave loop is much better at rejecting noise and produces a lower
angle of radiation for a given height than a dipole. I'd love to put up
a quad, but $600 is a bit much right now. A full wave loop costs almost
nothing by comparison. I'm wondering if perhaps a delta loop could be
effective as a portable radiator for the KX3. An inverted triangle fed
from the bottom apex seems simple enough.
With summer finally here it is time to pull out the boxes of wire, coax
and insulators and see what sort of interesting things to build.
Doug -- K0DXV
On 6/26/14, 4:07 PM, Vic, K2VCO wrote:
I have a theory about this.
Compare a vertical to a dipole. One reason for additional noise is
that a vertical is omnidirectional, and noise comes from all
directions. The signal is coming from one direction, and if it is the
right direction, then the 2.2 dB gain from directivity of a dipole
improves the s/n ratio by that much. But subjectively the difference
seems greater than this. It's also true that the vertical is better
for signals off the side of the dipole.
As Brian said, most verticals appear to be far noisier in urban
environments where there is a lot of manmade noise. I believe that
this is /not/ because manmade noise tends to be vertically polarized,
as is often said.
I believe that it is because most verticals are not adequately
decoupled from the feedline. Therefore, manmade noise is picked up on
the outside of the feedline and flows directly into the antenna.
This is exactly the same problem that happens with a dipole without a
balun.
Therefore the solution to the problem may be a good choke 'balun' at
the vertical's feedpoint.
On 6/26/14 1:38 PM, Brian Hunt wrote:
The other thing I have encountered with verticals vs horizontal antennas
in an urban environment is that verticals are inherently noisier.
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