Yep, rain static. I used to get this often when I operated mobile HF in
Florida. Whenever the rain drops were charged, the noise was always
proportional to the speed of the car. At about 60 mph I could sometimes
get S9+30dB in a 500 HZ bandwidth. When the rain drops were not charged,
there was little to no noise.
I never noticed the same thing on 2 meters, but I did notice an even
more curious effect. A lightning strike within a couple of miles would
sometimes cause the noise to jump to S9+ immediately after the strike,
and then gradually decrease to an insignificant level over a 30 to 45
second interval. I never did completely figure that one out. I'm sure it
had something to do with charge equalization between the ground and the
clouds plus corona possibly, but I'm not sure of any of the details.
Brad Pioveson W9FX wrote:
>On Christmas eve, I sneaked into the shack for a few minutes to seek shelter
>from the grandkids, and, I turned on the 2 meter rig - an FT-847 - the VFO
>of which was sitting on a beacon frequency I often monitor. Whoa! Talk
>about noise! What I heard and observed on the rig's S-meter was really
>something. The noise was semi-random, but, even the digital S-meter never
>managed to drop below S-9. There were pronounced peaks of a few tenths of a
>millisecond in duration, and, these, at three-to-five per second intervals.
>The noise was audible from 138 thru 155 Mhz - which is the limit of what
>knob-spinning I engaged in.
>My first thought was, of course, some new type of line noise had invaded the
>neighborhood, so, I twirled the antenna - a modified Cushcraft 3219 yagi -
>to determine the noise source's direction. It was the same around the
>compass with no peaks. Next, I hosed up the HF rig and listened on 40, 30,
>20, 17, 15, 12 and 10 meters. No noise to be heard, save for the usual
>low-level line noise I'm plagued with. Finally, I hooked up the 50 MHz
>antenna to the FT-847 - the antenna being a 2 ele quad. No noise there,
>For a moment or two, I was truly bewildered, and, wondered if the rig,
>itself, might be the culprit... I need to add, here, that the weather was
>abominable at this time - moderate to heavy rain, the drops seemingly
>abnormally large, and, it was cold - near freezing, but, enough above that
>temp so that no ice was forming. The wind was pretty gusty. In short, it
>was a miserably cold, wet winter day.
>So, as I sat pondering the new RFI situation, it occurred to me that what I
>might have been experiencing is what, from time to time, I have seen
>discussed on this reflector: Rain Static (?)
>This theory was later supported by the immediate cessation of the RFI
>coincident with the cessation of the rain.
>So, all of the above is presented to ask the question: Does what I describe
>accurately depict what one might find in a rain static situation? And, if I
>may ask a follow-up question: I've had this old CC yagi up for many years -
>it's probably well into it's 25th year. I've never heard anything like this
>RFI before...from any antenna, much less, this particular array. What might
>have changed, d'ya think? Oh - and, the antenna 'plays' as well as it ever
>has - no changes in the measured parameters, at least from the rig end of
>the coax cable.
>73, Brad, W9FX
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