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ESD Precaution When Switching Antennas




 
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Author Topic: ESD Precaution When Switching Antennas  (Read 583 times)
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AJ1G
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« on: February 28, 2020, 01:42:37 PM »

While switching antenna cables back and forth between my inverted vee and 75 meter inverted L/40 meter quarter wave vertical into my IC-7100 in the shack this morning, I observed that the received audio background noise took an immediate drop and then slowly recovered each time I plugged an antenna into the HF antenna jack on the back of the radio.  It then dawned on me that the receiver was most likely responding to an ESD pulse off the center conductor of the antenna PL-259 as I was plugging it in!  With all the wind we are having today, I suspect some pretty healthy static charges are building up on the unterminated feed lines.  Neither the inverted V or the inverted L/ vertical feed lines are grounded at any point until they are connected to equipment in the shack.  Whenever lightning storms are predicted, the feedlines which come into the house through a notch in the casing of a garage rear window adjacent to the equipment in the shack in the basement aree disconnected and physically removed from the house, and left coiled up on the ground below the antennas in the yard.  Since the dipole shield  of the coax and the radials for the inverted L/quarter wave vertical are elevated (and should not be grounded to a ground rod at the feed point to minimize a flanking path to ground which will reduce antenna efficiency), the shield sides of the feed lines can also build up a static charge.

Iíll be sure to temporarily ground out the feed lines prior to connecting
them in the future.  Wondering if connecting the coiled up feed lines below the antennas in the yard to a fully grounded for both center conductor and shield SO-239 jack on a ground rod would be a good idea or bad idea for further lightning protection. Iím thinking that grounding them vice just leaving them coiled up on the ground will result in a higher and more damaging current surge in case of a direct strike?

Iím posting this because I donít recall the possibility of static charges on antennas causing damage when connecting them to a radio being discussed before. I recall hearing about some old school tube type military receivers and transceivers being pressed into service in Operation Desert Storm because modern solid state receiver front ends were getting fried due to ESD from antennas in sandstorms.
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Chris, AJ1G
Stonington, CT
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« Reply #1 on: February 28, 2020, 02:05:22 PM »

One easy insurance policy would be to connect a Tee to the output of the RiceBox, running the antenna feed straight through, then putting a PL259 with a 100K metal film resistor  on the leg of the Tee.  Up through 30 mhz the match effect would be negligible if  the leads are short.  Left in place it would minimize the chance of cockpit errors down the road.  I keep similar commercial surge suppressors in front of my rigs.  Some of my antenna coupling units provide a DC ground through a center tap and some don't.    You can always use an RF choke similar to what you'd use in a transmitter but that gets big and glommy.
Years ago a friend had a big inverted L off his 100 foot tower, and it came straight into the shack to a tuner on the wall.  Wind static would make half inch arcs to ground and once he lit a cigar off it.  I gave him a big honking pi-wound choke that chilled it out.
73 de Norm W1ITT
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KK4YY
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« Reply #2 on: February 28, 2020, 02:49:12 PM »

On a previous 75M dipole, I used a 5.6k ohm 2W resistor across the antenna feed point. The idea was to give static build-up a path to dissipate with negligible loss of transmitted power. Assuming an antenna impedance of 50 ohms, the resistor would dissipate about 1% of transmitted power, or 1W out of every 100W. I can only guess about how effective it may have been at reducing static build-up. But, I figured it was better than nothing.


Don
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Patrick J. / KD5OEI
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« Reply #3 on: February 28, 2020, 10:35:07 PM »

A couple of those 'long' spiral-wound-looking 10 Meg high voltage resistors does a decent job here. They have too much resistance for the 'spiral' resistance stuff to act like a coil, that is, I have never blown one up from RF, and there is no static electricity from this dipole as they drain the current off faster than it can accumulate. YMMV

Guess it depends on how much current your antenna can collect as to the minimum value of resistance needed, which on any given day would depend on wind, humidity, height, sharp points, any storms, and length of the wire among other things.

Certainly 5.6K is well below the value which would permit any significant charge to accumulate on any ham's antenna, except maybe during a big thunderstorm when the antenna ought be grounded anyway.

There's a good article in Scientific American, May 1957, "Experiments Which Show That the Earth Functions As an Electrostatic Machine". 

The item is also in the 1960 book of projects for the amateur scientist by C. L. Stong, out of print but on amazon as are reprints.
Today they sell a CDROM edition with all those and many, many more science experiments including the good (dangerous) ones and more modern ones.
Just reading the experiments has taught me a lot of practical stuff.

Just remember, your head is 200 Volts above your feet. Good thing your body is not an insulator!



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Carl WA1KPD
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« Reply #4 on: February 29, 2020, 10:34:54 AM »

At the CT QTH I ran a standard 160-meter dipole. 2 x I had to return the Flex for front end antenna switching problems. Turned out that diodes had been zapped. For 2 years now in Maine I have run 270 ft of wire center-fed bu OWL. Based on discussions with Rob W1AEX I added this Surge Protector  https://www.arraysolutions.com/as-309h. So far no problems!
73,
Carl
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Carl

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Patrick J. / KD5OEI
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« Reply #5 on: March 07, 2020, 12:08:16 AM »

That box looks pretty good. I like the gas tubes in there.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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« Reply #6 on: March 07, 2020, 02:44:07 PM »

Novice days - 1961 or so -
I definitely recall my dad's reaction when he looked at my operating desk where I had left the coax to my dipole disconnected. The periodic arc from the PL-259 center pin to the shell had caught his eye and ear....From then on I stuck a 1/4-20 bolt in there to short things out......
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AJ1G
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« Reply #7 on: March 08, 2020, 01:39:03 AM »

I recall stopping the Crystal Radio Club W2DMC Field Day operation at a former Nike missile site on top of the Hudson palisades in Orangeburg NY in 1973.  Someone had put  up a long wire vertical suspended from a weather balloon, and there were thunderstorms moving in. At one point I grabbed the wire to work on its connector and got a terrific jolt from it....just like Ben Franklin.

Iíve seen and heard about too many lightning strike disasters to think that lightning arresters and gas discharge tube protectors on feed lines that are allowed to remain in the house during thunderstorms is adequate protection.  Here the feed lines always go
out the window and as far away from the him house.  I also disconnect the feed lines to any mobile rigs in the vehicles.

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Chris, AJ1G
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« Reply #8 on: March 10, 2020, 12:40:28 AM »

The static dischargers and etc., should not be confused with disconnecting the antenna from the house/shack. Mine's always disconnected except when in use.
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Dave K6XYZ
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« Reply #9 on: March 10, 2020, 11:37:03 PM »

I use one of the 8" long Array Solutions 'static bleeders' on my Hy-Tower.
It DC grounds the antenna....no more arcing coax.
The bleeder impedance makes it invisible to RF.

Don....I had the same arcing problem back in 61'...something woke me up in the middle of the night....started looking for an arc in my Ranger...then I made the mistake of removing the coax connector....yikes.
No more sleep that night...and I didn't go to sleep in class the next day either!



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