On 1/16/20 10:08 AM, VE6WZ_Steve wrote:
Over the years I have noticed my Beverage feed impedance will change during the
winter.
My station is configured to take analyzer sweeps in the shack of any of my 12
Beverage wires. All 12 wires show the same change in impedance compared to the
summer.
Two days ago I did some experiments to see if this was because the frozen
ground was limiting conductivity. In wet soil with the associated minerals and
salts, the ionic transfer contributes to conductivity, just like salt water.
When the ground is frozen solid, like a block of ice, it seems possible that
this ionic conduction could be diminished.
To test my theory, I add some radials to both the feed and termination and
rescan the Beverage.
Join me on the adventure to see how it worked out in this video as I brave the
-38 C winter cold. I also show some calculations of the effect of cold weather
on Beverage wire conductivity and the termination resistor. This is perhaps
the most interesting, because the term resistors I use are ceramic units which
have a significant negative temperature coefficient. I experiment to confirm
the changes in resistance with temperature.
this is quite interesting.. The epsilon of frozen soil is dramatically
lower than not frozen, and as you say, there's a difference in
resistivity. I've seen a fair amount of literature about sea ice vs sea
water, and I've been working with Lunar regolith simulants with various
amounts of ice content at HF frequencies recently.
What would be interesting is that as the soil freezes, the skin depth
will increase, so even though the top layer is frozen, at low
frequencies (where you're using a Beverage) there might be significant
RF in unfrozen soil. So the performance changes due to freezing might
not be as big as you might expect.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|