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40m dipole sparking in shack
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by KD4FOV on January 23, 2005
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Hello all,
During this weekends blizzard in the NE, I ran across something very interesting. During the heavy snowfall my shack developed a "spark" sound that occured every minute or so. I located the unlikely source. It was my 40 meter dipole that was just lying on a table unconnected and ungrounded. I summize it was the heavy snow causing a static build-up. I shorted the shield and center and grounded them both. This stopped the sparking. Has anyone seen this before? I wonder what the potential voltage was before it arced over?
73 de KD4FOV
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RE: 40m dipole sparking in shack
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by N4SL on January 23, 2005
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Hi, yes you are correct, while it's snowing heavily your antennas will accumulate a huge charge from "precipitation static".
I feed all my antennas with open wire line that enter via large dual knife switches. Sometimes it'll actually arc over the full 2", sometimes nearly continuously!
I assume when you said "...40m dipole, laying on the table.." you meant the connector on the coax that leads up to the antenna which is hanging in the air. If not, RUN LIKE HELL your house if full of ghosts.
So, ground your antennas you aren't using.
Some folks put these spark arrester things which are sorta like spark plugs that flash-over when the static charge gets too high.
73, Steve N4SL Snohomish, WA
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RE: 40m dipole sparking in shack
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by AA4PB on January 23, 2005
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Preciptation static build up is a fairly common occurance. It can also happen from wind, especially blowing dust over the antenna.
It probably takes several thousand volts to arc over the connector but the current is not very high. Grounding the antenna when not in use is one solution. You can also permanently place a large value resistor (like 1 meg) across the antenna to prevent the charge from ever building to the point where it will arc over. The large resistance will have no affect on the signals since it is so large when compared to 50 ohms. This assumes that the shield is grounded just before it enters the house as it should be for lightning protection.
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RE: 40m dipole sparking in shack
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by W5HTW on January 23, 2005
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Been bit many times by static electricity. Ground your antennas.
Think about this. If that antenna was still connected to a tuner, or a radio, it could be a very expensive repair job. I've had static take out the front end in a radio, and blow the diodes in the tuner that are used for the SWR bridge.
And it doesn't take snow. Wind, dry air, (low humidity) and a long wire and you have the makings of a radio-blowing discharge.
One of the most spectacular I witnessed, which was followed immediately by a long string of pervasive cursing, was when the engineer reached into the old 10 KW shortwave AM transmitter, which was disconnected from power and completely grounded. However, it was still connected to the antenna - a 1600 foot long, three wire rhombic at 100 feet. The arc from the antenna coil to his wrist was a good seven inches. And it DID leave a mark, though he was not seriously hurt.
Not even when he threw the tool box across the room.
Ed
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RE: 40m dipole sparking in shack
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by WX0B on January 23, 2005
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One of the better ways to deal with this is use a ligthtning arrestor that has a static bleed choke built into it.
Most do not. I am amazed at the number of hams that do not do anything about lightning protection, and static discharge. But are very vociferous when their $3,000 radio gets zapped.
Learn more about lightning protection and static discharge techniques here.
http://www.arraysolutions.com/Products/ice/
Read the special publications section about coaxial arrestors.
There are also arrestors for ladder line fans too which safely discharge static.
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RE: 40m dipole sparking in shack
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by KB9CRY on January 23, 2005
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If I may offer an additional comment to this comment:
So, ground your antennas you aren't using.
The static buildup and discharge that was noticed will also be happening to an antenna that is in use, as well as those that are not is use. Since you can't ground the antenna that is in use the only way to protect your front end from static discharge is to install an arrestor that will constantly drain away charge and still allow it to be used. As stated before, go to the ICE website via Array Solutions and also go to the Polyphaser.com website. Both companies sell essentially the same devices and both have tons of technical info that all amateurs should read and be knowledgable on. Personally I use ICE devices; believe me, they work. Phil KB9CRY
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RE: 40m dipole sparking in shack
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by AA4PB on January 23, 2005
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The static buildup and discharge that was noticed will also be happening to an antenna that is in use, as well as those that are not is use
---------------------------------------------------
It depends on the receiver design. If the receiver input offers a relatively low DC resistance to ground then the static charge will never build up while connected. However, if the receiver input is DC floating and connected to a FET or something then it can result in taking out the front end. Most receivers have some sort of DC path to ground to protect against this however, the safe thing to do is to protect it with a discharge unit, resistor, choke or something.
Don't forget, if static can build up enough to arc over the connector guess what happens when you have a nearby lightning strike that couples energy into the antenna or feedline?
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RE: 40m dipole sparking in shack
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by W0OX on January 23, 2005
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Many moons ago ( when I had brown hair ) and a crystal for 3730.. My buddy Bill and I made a long wire to use with our home brew tuner and his DX100..it was just short of four miles long. We connected all the electric fence on the farm. When the summer thunder boomers were approaching ..we had some big arcs (yes we then would toss the end out the window)Didnt work much DX but we sure played hell with the phone lines out in the country
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RE: 40m dipole sparking in shack
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by WA6BFH on January 23, 2005
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Yes, several years ago, during a Southern California “Santa Ana Wind Storm” I heard the unmistakable noise of high voltage leaking and discharge. The highest voltage I had on at the time in the shack (I thought) was 120 Volts AC -- way to low for such sound effects!
Then, my Astron VS-35M went into crow-bar protect. I reached forward to kill its power switch, and while my hand was still 5 or 6 inches from the power supply, an ark jumped to my hand that made it numb for several minutes. Also, the regulator chip was thus and truly! Fortunately the only damage was to that on “IC” in the supply. All the radios were good.
The closest thing to ground, for the leakage path of static voltage being developed across my antenna was in the power supply. The antenna that I used at the time worked as four separate half-waves for 70, and 135 centimeters, as for 2, 6, and 20 meters. The antenna also worked as a ¼ wavelength Ground Plane for 40 Meters, and ¾ wavelengths for 15 Meters. Five coax runs came into the shack but, there was no earth ground. After I fixed the power supply, I made a grounding path to protect for such high voltage bleed -off.
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RE: 40m dipole sparking in shack
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by WB6BYU on January 24, 2005
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A 10K or larger wire-wound power resistor (perhaps 10 watts)
makes a good static bleed when connected between each
feedline and ground.
The third wire of your power supply line cord should
ground the power supply chassis, and the rig connected
to it. This SHOULD be adequate to relieve any static
pickup on the antenna, as long as the center conductor
is at DC ground somehow. Otherwise, any ground wire,
even if it is too long to act as an RF ground, should
work.
I had a portable station in Alaska once where the variable
capacitor in the antenna tuner started arcing over every
few seconds or so. I solved it by running a wire out
the window and wrapping the end around a BBQ skewer
stuck in the ground. The resistance was low enough
to drain off the static charge, at least temporarily.
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