[50mhz] Ground gain vs antenna polarization

[Paul Kelley N1BUG]

Hi Lance,

Thanks for that information. I recall reading somewhere long ago 
about reduced ground gain with vertical polarization but couldn't 
recall any details. I have no idea where I read it. It may have been 
the same study you mentioned. I'm afraid I have forgotten much from 
my EME days!

I think part of the situation with antennas of different heights on 
terrestrial modes is the angle of signal arrival. Since the peaks 
and nulls in the vertical pattern vary with antenna height due to 
ground reflections, it seems plausible one might have a signal in a 
null on a high antenna but in a peak for a lower antenna - or vice 
versa. But polarization may very well play a role, as you suggest.

Years ago I noticed a very pronounced "flutter" on meteor scatter 
signals at 144 MHz. It wasn't until many years later, running 
FSK441, that I clearly saw the rapid fading during longer bursts. It 
would be very interesting to know the cause. Perhaps it would be 
enlightening to do some meteor scatter with circular polarized 
antennas and see if the fading is still evident.

73,
Paul N1BUG



On 6/27/2011 3:15 PM, Lance Collister, W7GJ wrote:
> Hi Paul,
>
> I recall reading something from Europe about a study that showed
> vertically polarized signals with ideal ground gain were about 3
> dB less than horizontally polarized signals.  I also made a
> number of contacts with NL7Z on 6m EME when he was using his pair
> of 6 element side by side yagis, vertically polarized.  It was
> apparent that the main lobe of that array was higher than would
> have been expected for a horizontally polarized array.
>
> Which leads me to wonder about the difference in signal strength
> between incoming signals of different polarities, if an antenna's
> best reception of the different polarities is at different
> elevations.  Many people on 6m make remarks such as "he was Q5 on
> the lower antenna but I couldn't hear him at all on the higher
> antenna".
>
> I have been told that polarity makes no difference on ionospheric
> propagation because the signal is scattered into all polarities.
> However, I wonder whether some of what people are actually
> perceiving as differences in elevation of ground gain lobes
> between different height and gain antennas might also be due to
> differences in polarity between incoming signals.  Unfortunately,
> there are not many of us with huge rotating towers who could
> easily mount antennas of different polarities and switch between
> them.  If that were the case, the innovative receiver from HB9DRI
> might be a very interesting way to automatically maximize the
> incoming signals:
>
> http://www.linkrf.ch/
>
> I have recently begun using FSK441 to collect rare gridsquares
> out west, and was immediately struck by the very pronounced 1
> second fading that is clearly displayed on the SpecJT waterfall
> when longer bursts are received.  I don't know what is causing
> this rapid very regular QSB, but the first thing that came to
> mind was Faraday rotation.  The signal traces basically look like
> someone dipped a paint roller partially in a pan of paint, and
> then rolled it across the computer screen!  I think it would be
> very interesting if someone did some research to determine if
> the signals are in fact peaking up in the opposite polarity
> during the nulls during such a meteor burst.  I think it would
> also be very interesting to learn whether there is in fact a
> large difference in signal strength between "ionospherically
> propagated" 6m signals of difference polarities.
>
> Paul, I apologize if all this has already been discussed and
> covered somewhere.  I am just a student of this Magic Band, and
> find these anecdotal observations very intriguing.  GL and VY 73,
> Lance