[600MRG] [DETECTED AS SPAM] Re: Rain amplitude modulation

[kl7aj at acsalaska.net]

Hi Merv, et al:

    I worked in broadcasting for (eesh...I hate to even think how long...HI).... up here in the world's worst ground conditions.   The change in conductivity between summer and winter was tremendous....a full time job just keeping a two-tower array in line.   In general, it's the amount of salt in the ground (not necessarily sodium chloride) that determines just how much the conductivity changes.  When it's dry, the conductivity is zilch; when it's wet the salt goes into solution and becomes electrolytic.   If there aren't many salts in the ground, then the conductivity stays lousy all year. :)


 

---
Eric P. Nichols, KL7AJ
AlasKit Educational and Scientific Resources
3763 Lyle Avenue
North Pole, AK 99705
(907) 488-0483
(907) 371-7120
http://alaskit.co




On Fri, 16 Mar 2018 07:16:28 -1000, Merv Schweigert via 600MRG <600mrg at mailman.qth.net> wrote:
 

Any reflection perhaps on the quality of the ground system in use for so much
change in R at the antenna with ground moisture?

Merv K9FD
 




Tnx Ben. That was quite revealing. I did not know it could have that much of an effect.

 

Neil, w0yse

 


Sent from Neil's iPad....





From: 600mrg-bounces at mailman.qth.net <600mrg-bounces at mailman.qth.net> on behalf of Ben Gelb <ben at gelbnet.com>
Sent: Friday, March 16, 2018 7:58:33 AM
To: Posting 600m 600mrg
Subject: [600MRG] Rain amplitude modulation

 




We've been getting some rain in the SF Bay Area finally, which has presented a fun opportunity to observe fluctuations in ground losses during rain events. Below are some plots from last night of the R component of my antenna impedance (captured while WSPRing) as well as some precipitation data from a local weather station.

 

I retuned the antenna a few weeks back to present right around 50 ohms to the TX. Last night it ranged from about 35 ohms to 48 ohms (or really 140 to 192 ohms before the transformer). Rr is estimated at about 0.2 ohms, so that variation is really all variation in ground loss (and I guess a pretty large corresponding change in antenna efficiency).

 

Maybe a really clever WSPR listener could estimate the rate of rainfall at my QTH based on changes in signal strength... hi.

 

Hopefully the plot images come through... or everyone is going to wonder what I'm talking about!

 

My measured feedpoint resistance (stepped down from loading coil by 4:1 ratio).

 


 

 

Rainfall data from the Weather Underground station in my neighborhood (wraps at 12 midnight, so you have to use your imagination to fix the line, but there's a big step from the downpour around midnight):

 
73,

Ben N1VF


 

 
 

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