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Old February 7th 20, 02:49 PM posted to rec.radio.amateur.moderated,rec.radio.amateur.antenna
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Default [KB9VBR] Does Snow Affect Vertical Antenna Performance


KB9VBR J-Pole Antennas

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Does Snow Affect Vertical Antenna Performance

Posted: 06 Feb 2020 08:09 AM PST
https://www.jpole-antenna.com/2020/0...a-performance/

Last weekend we received one of many of the winter storms we usually get
this time of year. This one dumped about 6 inches of snow on us. So when I
posted a picture of my Wolf River Coil in the backyard with the snow
creeping up to it‚ Andy asked the following question:

Have you noticed the snow changing the tuning points? Mine has required me
to tune longer, as the swr dip had moved after snow. A benefit is that Ive
had lower swr after tuning, than I did without snow. Maybe include this in
a Q&A if there is a correlation between snow and the ground
conductivity/swr?



That’s a really good question. We know that ground conductivity can affect
the performance of your radial system. Different types of soil will offer
different performance characteristics. If the soil is moist‚ the ground
will offer better performance. For example rich moist soil has more
conductivity than dry‚ hard‚ or sandy soil. And of course water has
extremely good conductivity. That’s why if you are operating radio on the
beach you’ll want to throw your ground radials into the water. But what
about snow? Does burying your radials in snow make a difference? I thought
I would do a couple of tests to find out.
Last November I set this Wolf River Silver Bullet 1000 coil in my backyard.
The antenna is on a short fence post and I’m using three ground radials of
32 feet each in length. When I set up the coil I recorded some measurements
with my Rig Experts antenna analyzer so I thought I’d take a new reading
now to see if there is a difference. In order to make sure the collar is in
the same position as my previous readings- I used this jig to readjust the
collar. I made the jig last fall when i tuned the antenna so it was easy to
go back to the same spot as my previous test. So lets go inside and see
what the numbers say.
The premise is that the snow will cause the tuning to go long and it
appears that may be the case- although in my case the amount is very
slight. We can see between the two scans that the curve shifted a bit up in
frequency and the SWR increased a little. But the SWR increase was slight
and still under 1.5:1. Moving on to the impedance and reactance- both
scans: the dry ground and snow covered ground are virtually identical. So
even though there is a slight increase in SWR and shift of the resonance of
the antenna‚ it is very small and in most cases you wouldn’t notice the
difference.
I tried searching for any research that would give me any explanation of
what’s happening. My copy of the ARRL Antenna book wasn’t helpful as it had
no information pertaining to snow. I found some anecdotal information in a
few ham radio based forums and a mention in the ITU’s Handbook on Ground
Wave Propagation that said: and I paraphrase: In some cases there may be
seasonal variations in surface wave propagation- to freezing conditions
where water becomes ice‚ or to thick snow cover where these may cause
changes in the effective ground conductivity. All of these change may
affect the intensity of the surface wave field. In particular such seasonal
changes may result in a reduction in strength in summer. So snow could
possibly enhance winter propagation- but I think there are too many
variables in the type and consistency of snow that would make it difficult
to reliably say snow increases propagation.
Now I will admit that my ground radials are made of insulated wire so the
snow really isn’t in contact with the bare conductor of the radial. I don’t
think this would make much of a difference though as snow‚ especially dry
snow‚ is a poor conductor. So I think the bottom line is that the snow
covering the radials doesn’t make much of a difference in the overall
performance of the antenna.
So bottom line- Snow can affect your SWR and tuning and it may give you
some ground wave propagation effect. But other than that‚ radio waves seems
to be blind to its presence. Of course if your antenna’s radiators are iced
up- this could be an issue; otherwise head outside and go play radio in the
snow.
What do you think? Have you had a similar experience with snow covered
ground radials? Am I off base in my assumptions? Leave a comment below. If
you could link to some resources on this subject that I may of missed‚ that
would be greatly appreciated. We’ll follow up on this in the next Your
Questions answered video.



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