[600MRG] Rain amplitude modulation

Fri Mar 16 23:15:14 EDT 2018

Glad folks found this interesting.

I think Merv nailed it - my ground system is pretty terrible. Probably
10-12 short radials, and really only spread out over one quarter of the
circle... I imagine a better radial field would reduce the variation a lot
(and also just bring the baseline impedance down substantially - 200 ohms
is pretty high!).

There is ~5-6 ohms variation in X as well in the dataset from yesterday
(not sure which direction as the AD8302 doesn't say, and I didn't do any
manual tuning around to figure it out). I also don't trust this measurement
very much because I haven't attempted any calibration of the phase detector
(only magnitude has been measured/calibrated). On my TODO list but haven't
got around to it yet.

As Ike mentioned, I do see a 10-15% difference in input/output power to the
transmitter depending on the conditions (TPO seems to drop when impedance
drops, which is a bit counterintuitve.. maybe has to do w/ change in X? Not
sure. Would sort of think it'd go the other way..). Been thinking about
adding some relays on the matching transformer to be able to adjust.

I remembered I have some inground sprinklers in the backyard I never turn
on... hmmm sounds like next experiment...

Have a good weekend all! :)

73,
Ben

On Fri, Mar 16, 2018 at 1:47 PM, Laurence KL7 L <
hellozerohellozero at hotmail.com> wrote:

> hi Ed - 474 wspr 2 rx is online  in wasilla +24 between tx sessions
>
> Laurence KL7L
>
> On Mar 16, 2018, at 8:21 PM, Edward R Cole <kl7uw at acsalaska.net> wrote:
>
> 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).
>
> [image: []]
>
>
> 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):
> [image: []]
>
> 73,
> Ben N1VF
> ______________________________________________________________
> 600MRG mailing list
> Home: http://mailman.qth.net/mailman/listinfo/600mrg
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:600MRG at mailman.qth.net <600MRG at mailman.qth.net>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
> ______________________________________________________________
> 600MRG mailing list
> Home: http://mailman.qth.net/mailman/listinfo/600mrg
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:600MRG at mailman.qth.net <600MRG at mailman.qth.net>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
> 73, Ed - KL7UW
>   http://www.kl7uw.com
> Dubus-NA Business mail:
>   dubususa at gmail.com
>
> ______________________________________________________________
> 600MRG mailing list
> Home: http://mailman.qth.net/mailman/listinfo/600mrg
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:600MRG at mailman.qth.net <600MRG at mailman.qth.net>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
> ______________________________________________________________
> 600MRG mailing list
> Home: http://mailman.qth.net/mailman/listinfo/600mrg
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:600MRG at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/600mrg/attachments/20180316/3ff38588/attachment.html>