Re: Need K3 dB Measurements on new 160M Antenna

Posted by Don Nelson on Aug 29, 2010; 12:16pm
URL: http://elecraft.85.s1.nabble.com/Need-K3-dB-Measurements-on-new-160M-Antenna-tp5468244p5474860.html



Geoff,

To do good antenna testing you need an anechoic chamber or better
operate in deep space. My primary interest in radio are the microwave
bands. I do set up antenna ranges for 10 GHz (3cm), In doing so, I find
the wind blowing tree leaves will have a non trivial affect on the
observed signal even though the trees are "out of the way." I find that
I need to place the reference antenna and the antenna under test in
exactly the same place (x y and z position) to get true A/B comparisons.
This is demonstrated by taking two known antenna and see how repeatable
the observations can be.

Scaling these realizations up to HF antenna causes me to throw up my
hands. Yes we do the best we can testing antenna, but we have to be
realistic about the data we collect. When anyone makes claims about
their antenna I listen carefully for the details on how the antenna was
tested.

Maybe we should ask ARRL to fund a synchronous satellite over the US
with a beacon on each of the HF bands so that we can point our antenna
up and make more valid comparisons.

Don, N0YE





On 8/29/2010 5:22 AM, Geoffrey Mackenzie-Kennedy wrote:

> David,
>
> 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.
>
> Unless the vertical patterns of the A and B antennas are very similar in
> shape and lobe take off angle, it can be seen that changes in the angle of
> arrival of the test signal would introduce errors to the results of "on-air"
> tests.
>
> I have no experience with 160m, but on 40m for example the change in the
> angle of arrival of short path signals from the East Coast and Midwest can
> be large, and can change rapidly. Sometimes my dipole 70ft AGL which is
> end-on to the States, a "cloud`warmer" in that direction, will outperform a
> 40m beam pointed at the States - a disturbing result if taken to be the true
> performance of the beam.
>
> IMHO "on air " antenna tests need to be repeated many times over a fairly
> long period, preferably with the same stations.
>
> 73,
> Geoff
> GM4ESD
>
>
> David Cutter wrote on Sunday, August 29, 2010 6:36 AM
>
>> I would try a chart recorder in this arrangement; there's no mistaking
>> which
>> channel is which.  Of course use a modern version using pc sound card then
>> you can squash up or expand the results for examination.
>>
>> David
>> G3UNA
>>> Alas, after years of doing A/B manual coax switch tests, I have given
>>> up on that exposing anything better than 10 db differences on anything
>>> other than stable local signals.  And that is suspect because it is
>>> often ground wave, which bears no resemblance to sky wave.
>
>
>
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