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Re: [TowerTalk] Rain Induced Voltage

To: "Dennis OConnor" <>,<>
Subject: Re: [TowerTalk] Rain Induced Voltage
From: "K8RI on TowerTalk" <>
Date: Fri, 1 Dec 2006 15:12:42 -0500
List-post: <>
Good old precipitation static. I think it's sorta like a giant Vandergraph 
generator and there is no convective activity within a distance to induce 
anything more than QRN.  Tops are only 5 to 10,000 in most of the area with 
the occasional 15,000. Midland, Gratiot, and Saginaw counties are less than 

Now that we have wet snow and wind I'd bet the voltage level and rate of 
charge has picked up substantially.
Winds are showing as 30 to 35 at times.

Some years back. Actually it was a lot of years back when I was just 
building the place over at Breckenridge. I had a temporary 40 meter vertical 
mounted on a pop bottle for a base insulator. One day we were getting heavy 
snow along with lots of wind.   I heard this very loud popping sound. When I 
went into the room where the radio station was located (coax was 
disconnected) it sounded more like a small caliber rifle shot.  I spotted 
the arc at the PL259.  It was a big, fat, blue arc that extended well out 
from the connector and put any ignition system I've ever worked with to 
shame and it was doing it at a rate of about 1 to 2 per second.

For those who have never experienced it (I know Dennis has) it can be 
Those with grounded antennas such as my VHF and UHF yagis you may hear some 
but it doesn't generally show up as more than a couple of volts on the coax. 
But antennas like my half sloper on 160 are something else if not grounded. 

There's usually not much current available after the initial discharge and a 
VOM has a low enough resistance to bleed off most of the charge which 
prevents the voltage from climbing.

However for those who are an advocate of disconnecting things, if you do so 
with an ungrounded antenna system such as a dipole where the only electrical 
ground it through the chassis of the rig don't just throw the coax on the 
floor.  That coax is likely to become *hot* as in electrically hot becoming 
many thousands of volts above ground. Hot enough that it can be like 
grabbing an electric fence or the ignition wires on a car. I'd mention the 
old telephone magnetos but I doubt many remember them. <:-))

Actually it's possible at times for those cables to become hundreds of 
thousands of volts above ground and if the antenna is large and the coax 
long there can be enough capacitance for a substantial charge.

> This morning in Michigan we are having a mix of sleet and freezing rain... 
> I was up early so I wandered out to >the shack about 5AM to see if any 
> Pacific DX was coming in on 80 or 160...  When I energized the antenna

That's before I went to bed.  I lose track of time out in the shop...or 
working on computer, or reading, or...

>switch I was greeted by the sound of a frying/popping noise at about 4-5 
>cycles per second and an S-meter >completely pinned to the right...  I know 
>that sound quite well and instantly cut the power to the antenna >switching 
>box...  I unscrewed the coax to the one antenna that is not link coupled - 
>meaning I have a DC >connection to the actual antenna - a 160 meter 
>dipole...  Using the tip of my pocket knife I can draw an arc >between the 
>shell and the center pin on the PL-259... The VOM reads from 5 to 7 volts 
>DC across the >connector continuous into a 1 megohm load...  There is no 
>convective activity in the area, no thunder or >lightning, and no thunder 
>storms predicted...  The voltage appears to be induced by the rain drops 
>dripping off >the antenna wire removing
> electrons and leaving a static charge with the  ungrounded side of the 
> antenna <coax center pin) left positively charged...

Coming out of Kansas in some really rough weather all of my radios quit. 
First to go was the DME, then VOR/RNAV. Even the ADF (LF) and 
communications (VHF) went out. I turned the master off, then back on. 
Everything worked again.  A few minutes later I had to do it again.  I had 
to explain to ATC why they were losing my transponder return occasionally. 
Apparently the charge or discharge was enough to saturate the inputs of the 
receivers to the point where they could no longer hear the stations. 
Admittedly the wind was a tad faster, but I think it's still the same 

My station antennas for 160, 75, and 40, go through a remote switch. Each 
has a current balun at the antenna and the shield is grounded at the switch 
in addition to where it comes in the house where it also goes through a 
polyphaser. When unpowered all of those lines are shorted to ground at the 
remote switch.

> I know we have genteely discussed this before <called a scrum in some 
> circles>, but since it is fresh in my mind, I thought I would bring it up 
> again <also known as stirring the pot>...

Still we do well to remember how much voltage Mother Nature can develop even 
without thunderstorms. <:-))

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
> denny / k8do
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