[600MRG] Rain amplitude modulation

[Neil Klagge]

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).

[cid:ii_jeu28v0m1_1622f4a70b955303]


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):
[cid:ii_jeu265b90_1622f4884bcf2c75]

73,
Ben N1VF
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/600mrg/attachments/20180316/8da41ede/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 62259 bytes
Desc: image.png
URL: <http://mailman.qth.net/pipermail/600mrg/attachments/20180316/8da41ede/attachment.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 81549 bytes
Desc: image.png
URL: <http://mailman.qth.net/pipermail/600mrg/attachments/20180316/8da41ede/attachment-0001.png>