On Sun, 05 Mar 2006 19:29:12 -0500, Mike Coslo
wrote:

Based on another thread a few weeks back in which Horizontal dipoles
were being compared to Vertical antennas, and from a little chiding from
Roy, W7EL, I decided to do some testing on my own personal versions of
the two.


Mike, this sounds interesting.

My setup is:

Icom IC-761
Antenna 1 - Homebrew OCF dipole at ~ 50 feet.
Antenna 2 - Butternut HF6V -ground mounted and 18 radials on the ground.


Question, does the magnitude of feedline radiation from the OCF
(presumably predominantly vertical) significantly affect qualification
of it as a horizontal antenna?

Another, are the antennas coupled significantly, eg is one within the
near field zone of the other? It is pretty hard to avoid in a
residential block on the low bands, and it will confuse the results
somewhat.


Part one of this experiment is to calibrate the S-meter. I found that
trying to calibrate the thing with on-air signals was a nuisance, and
probably wouldn't be as accurate, so I used a signal generator.

I started out with a +20 signal, then worked my way down.

+20 start
S9 -18 db
S8 -23 db
S7 -26 db
S6 -29 db
S5 -32 db
S4 -35 db
S3 -37 db
S2 -39 db
S1 -41 db

Not only is the shape of the scale an issue, but the granularity or
resolution, especially with LCD meters, or any meter where there are
discrete steps in the meter current (such as where a D/A converter
drives the meter movement).

If you want to move beyond S meters, you could try FSM
(www.vk1od.net/fsm) and organise some constant carriers at known
distances / radiation angles that you could make a series of
measurements of and produce summary statistics (median and inter
quartile range) for each antenna type.


All in all, I would have to say that the meter tracks very well from S8
to S4, and the only place that wasn't that great was from S9 to S8. But
considering the transient nature of the signals we are receiving, I
would have to day that the S-meter is of reasonably close accuracy.

With my newly calibrated S-meter I am ready to start looking at what the
two different antennas are doing for me. I have a coaxial switch to jump
back and forth between the two. My initial impressions are that there
are some surprises. The difference in noise levels varies by antenna by
band. On some bands the vertical is noisier, and on others it is the OCF
dipole. Especially intriguing is that on PSK mode, where I can see
several signals at one time, switching between antennas will attenuate
some signals, while other signals increase in strength. I think that my
vertical works better than I gave it credit for, but If I definitely
want *both* antennas.

I described a technique for assessing the relative performance of
mobile stations by having them transmit known constant carrier, each
station space about 200Hz and turning circles in a carpark near each
other, and to observe them at typical propagation distances with an
audio spectrum analyser, watching the relative strength of the
carriers.

Your PSK setup is affording you the same type of comparison, and
provides a ready (and recordable) assessment of the relative strength
of the stations under the two antenna scenarios. Be great if you could
orchestrate stations at known distances as part of an organised test.


Owen

Next installment will be the band to band comparison of the two antennas
with some numbers.

Installment three will be an investigation of that PSK signal strength
business.




- 73 de Mike KB3EIA -
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