[600MRG] Rain amplitude modulation

[Edward R Cole]

I found that I had to add two turns on my loading coil in winter as 
frozen soil had lower conductivity.  I attached leads to the two tap 
locations so I t only required moving my short antenna leader to the 
proper tap wire that uses a 1/4-20 brass stud.  I use about three 
foot of RG-213 center conductor as leader (shield un connected either 
end).  My antenna is back in the air and only awaiting retuning from 
495 to 473 KHz.

73, Ed - KL7uW

At 09:33 AM 3/16/2018, kl7aj at acsalaska.net wrote:

>By the way, don't ignore the REACTIVE component of the 
>impedance!   Ground conductivity is a COMPLEX number, containing 
>both a resistive AND a capacitive (dielectric constant) component, 
>the latter of which can affect reactance significantly.   The reason 
>for this is the REFLECTED signal (ground image) signal has a virtual 
>depth dependent on the dielectric constant.   A change in this has 
>the same effect as changing your antenna height....which, of course, 
>reflects in BOTH reactance and feedpoint resistance.   EVERYTHING 
>interacts with everything else.   This is why RF is so much fun. :)
>   ---
>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 15:54:23 +0000, Neil Klagge wrote:
>
>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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73, Ed - KL7UW
   http://www.kl7uw.com
Dubus-NA Business mail:
   dubususa at gmail.com 
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