Re: Need K3 dB Measurements on new 160M Antenna

Posted by Alan Bloom on Aug 29, 2010; 6:34pm
URL: http://elecraft.85.s1.nabble.com/Need-K3-dB-Measurements-on-new-160M-Antenna-tp5468244p5475575.html

In a previous life I was a radio operator at W1AW for several years.  I
think it was about 1974 when the new 120-foot tower was installed.  We
wanted to compare the big (700 feet long as I recall) rhombic we had
previously used on 20 meters for the bulletin and code practice
transmissions with the new stacked Yagis on the 120-foot tower.  Both
antennas were pointed due west from Newington, CT.

So for a week or so a special CW bulletin was sent asking for reports of
the relative signal strength of the two antennas.  CW bulletins are sent
several times a day so we covered the different propagation conditions.
The test consisted of several iterations of sending "antenna A" or
"antenna B" followed by several seconds of key-down.  The antenna
assignment changed randomly between bulletins so people wouldn't know
which was which.  Listeners then sent in QSL cards with their signal
reports.

I was assigned the task of analyzing the data.  There was some variation
among stations, but we had enough reports to get consistent results.  I
plotted the relative signal strengths on a map of the United States.

The result was that, right on the bore-sight of the antennas (the
great-circle path from Newington to southern California) the two
antennas were just about identical.  However, as you moved up the
Pacific coastline, the stacked beams started to do better than the
rhombic.  By the time you got up to Oregon and Washington state, the
beams were consistently an S-unit or two better.

It makes sense.  For a given gain, stacked Yagis have a much broader
horizontal beamwidth than a rhombic.  It was nice to see theory
confirmed by measurement.

Al N1AL



On Sun, 2010-08-29 at 10:49 -0700, Jim Brown wrote:
> On Sun, 29 Aug 2010 12:22:22 +0100, Geoffrey Mackenzie-Kennedy wrote:
>
> >The question remains IMHO whether the data taken from short term "on-air"
> >tests over distances which involve ionospheric propagation is useful in the
> >first place.
>
> Clearly any such testing requires the averaging of a large number of samples,
> and careful comparative tests. That is exactly what I am trying to do -- a
> large number of samples, carefully taken and carefully averaged.


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