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Static shock while connecting ground-wire to radio?

Posted: Sun Mar 01, 2020 7:49 pm
by JEL
I just got a fairly surprising electrical-shock while connecting a ground-wire to an antenna-connection, and have a question about it (And this is for radio-reception only, not transmitting)

It felt the same strength as those you can get from touching a TV-antenna plug (When connected to the TV-provider's wall-outlet)

Here's what I have done:

I have mounted an outside vertical loop antenna.
It's a rectangle with several turns. It's about 5 meters wide and 2 meters tall. The bottom-wire runs along the ground, but it's insulated copper-wire so no direct connection with the ground.

It's plugged to an antenna coax-cable, so that part is obviously bare to the elements (At least the shield)

No problems with any of that.

But then I layed out a 15 meter long copper-wire around the perimeter of my garden and buried the ending of the wire about 30 centimeters into the earth. This end-part of the wire is un-insulated (But not the main-run of the wire), so the bare copper sits directly into the earth about 30 cm down.

Now it gets dicey.

I then, without wearing gloves (Which I, from experience, normally do when handling anything electrical, but didn't think was necessary with this passive antenna-wiring), took the other end of the ground-wire (The part sitting at the end where I connect the antenna-cable to the radio) and wanted to connect it to the splitter so it connects to the shield-side of the antenna-cable.

Then I got electrocuted...
Not super-strong or anything, but enough to surprise me considerably and make me wonder if I have put my radio at risk (And possibly even my health)

Buit is this a good sign meaning the ground-wire is eating up the static-electricity, or a bad sign and something I should avoid using.

I have it connected at the moment and it lowers the noise-floor and enhances the SNR dramatically (And the radio still works, so I'm not sure what to think here)

I'm not overly concerned, because, as said, the TV-antenna does the same thing (I never touch those without gloves, because the shocks actually do feel annoyingly strong) so I'm thinking it's within the tolerable normal limits.

But still, this ground-wire is not connected to anything, just stuck into the earth, so obviously there is some fairly strong power coming from somewhere. Would that possibly be the vertical-loop antenna?

The vertical-loop antenna is made up of 100 meters of wire, turned into the rectangle with the dimensions I mentioned at the beginning of this post.
It's completely passive and I'm not using a balun or unun or anything like that. Just the wires connected to the radio's antenna-input.

But can a passive antenna like that really create such a huge electro-shock?
I always thought it was some kind of amplifier the TV-antenna used, which caused the shock, but perhaps I'm wrong about that.

Anyway, if anybody has some input regarding this, I'm very interested in hearing what you think.

Touching the antenna-wire and the ground-wire separately did not generate any kind of electric sensation. But when touching them both at the same time (When I wanted to connect them) I first felt a bit of jitter-sensation in the finger and then the full-on 'vibration'-like electro-shock.

I'm clearly an amature at this, but having had huge outdoor CB-antennae before I have never experienced any kind of electric-shock from any passive antenna before.

The radio is an Airspy HF+ discovery connected via USB to a PC, so I'm guessing that side is safe.

Pardon the long post here, but it's partly due to the very surprising shock I got :)

Re: Static shock while connecting ground-wire to radio?

Posted: Mon Mar 02, 2020 2:15 pm
by VE3EAR
I would be wary of connecting the antenna to your Airspy receiver directly, as it could easily be damaged by the "static" electricity. I recommend that you make up an isolation transformer, AKA a galvanic isolator, to protect your receiver.

You can make one from a toroid core removed from a computer power supply, and a two lengths of wire. Do a Google search and you'll find directions on how to make it and connect it between your antenna and the receiver.

73, Bruce, VE3EAR

Re: Static shock while connecting ground-wire to radio?

Posted: Mon Mar 02, 2020 2:44 pm
by JEL
Thanks. I should look into that I suppose.

I tried touching the wire today and there was nothing, and the radio runs at the moment with no issues and great reception.

I thought the ground-wire was there to take up the potential static-electricity though, and that the shock I got was from it balancing out the potential between the loop-antenna and the ground-wire.

It's connected on a Y-splitter (As per the instructions I found on a website about a loop-on-ground antenna)
(Antenna on 1, ground-wire on 1 (Only the shield), and radio on the last)

Re: Static shock while connecting ground-wire to radio?

Posted: Mon Mar 02, 2020 7:38 pm
by JEL
VE3EAR wrote:
Mon Mar 02, 2020 2:15 pm
Do a Google search and you'll find directions on how to make it and connect it between your antenna and the receiver.

73, Bruce, VE3EAR
Would something like this commercial product make sense (As an amature I think a DIY on this occasion may not be the best option. Not so much the building, but rather obtaining the proper items)

https://www.bonito.net/hamradio/en/galv ... or-gi1000/

It's a concept I have never come across before (But then, I have always only used commercial equipment earlier. It's only in the later years I have started tinkering with DIY antenna-setups :) )

The ground-wire I already installed on the T-splitter is not enough? (It's a long copper-wire, connected to the shield-side only, attached to the T-splitter where the antenna and the radio are also attached, and ends un-insulated ~30 cm (~1 foot) under the lawn (Buried directly into the ground-soil))

And given the loop is technically a short-circuit, although a 100 meter long wire, this ground-wire must electrically be connected to both the center-conductor and the shield.

I used an Ohm-meter (A multi-meter) and got a tone when testing the antenna-plug to see if center and shield is short-circuited.

But I still need the galvanic isolator?

Thanks again for your help Bruce.
jacob.

Re: Static shock while connecting ground-wire to radio?

Posted: Mon Mar 02, 2020 8:40 pm
by JEL
Short update; I just measured the antenna-plug and get voltages up to about 0.2 VAC and no detectable Amperes.

The multi-meter also has a light that lights up when held near a power-line (Used to search for power-cables hidden in walls and such. The normal ones for regular house-appliances and such. 220 Volts in Europe)... and that lights up when I hold it near the antenna-plug (I'm not sure what to take from that though, since I can also get it to light up by rubbing the meter across a wall, similar to what you would do with a balloon to build up a static charge)

Static electricity built up over time

Posted: Mon Mar 02, 2020 11:14 pm
by snn47
I guess you are experiencing static electricity built up over time. If you have a coax cable then the capacity, wich will vary with cable type and length, the static electricity will accumulate over time.

Did you have a thunderstorm building up in your area when you experienced this? The static electricity built up over time on a 10 m 1/4 Lamda ground plane was enough to generate sparcs over several milimeter at the end of ~10 m RG-213 open coax.

The voltage you meassure depends on the internal resistance of the voltmeter the lower the less voltage you meassure. If you have a bleeding resistor connected across center/outershield the static electricity builtup is limited to safe levels.

Re: Static electricity built up over time

Posted: Tue Mar 03, 2020 2:16 am
by JEL
snn47 wrote:
Mon Mar 02, 2020 11:14 pm
I guess you are experiencing static electricity built up over time. If you have a coax cable then the capacity, wich will vary with cable type and length, the static electricity will accumulate over time.

Did you have a thunderstorm building up in your area when you experienced this? The static electricity built up over time on a 10 m 1/4 Lamda ground plane was enough to generate sparcs over several milimeter at the end of ~10 m RG-213 open coax.
I mounted the antenna itself in the afternoon, so that part would only have been exposed to the elements for a few hours when this happened.

I do have a standard 10 meter sat-box coax-cable (75 Ohm) between the window and the antenna-wire though.
That cable had been out for a few days, since I had used it to test a different loop (A similar setup, except that wire was 'only' 25 meters long and only 1 turn, to test if it was worth building the 'big' on permanently)
I did not have the ground-wire on that one though, but used another loop (About 20 meters long and 1 turn) as the ground-wire during that test (Also placed outside).
So technically 2 loops, of similar size but different outside placements, in parallel.
I got no jolts from that.

It was only after the 'big' 100 meter long wire loop (Which is 6 turns) was mounted and I wanted to attach the open-ended ground-wire to the T-plug near the window (With the far end stuck into the soil) that I got zapped.

The weather has been stormy in the past week, but on the day I mounted the 'big' loop it was fairly calm. 5 degrees Celsius, sunny, but not much wind.
The 10 meter coax-cable had been out during the stormy week, but I handled that several times on the day I mounted the 'big' loop with no zaps.

snn47 wrote:
Mon Mar 02, 2020 11:14 pm
The voltage you meassure depends on the internal resistance of the voltmeter the lower the less voltage you meassure. If you have a bleeding resistor connected across center/outershield the static electricity builtup is limited to safe levels.
I have read about the bleeding resistor suggestion, but people say it doesn't make sense on a short-circuit loop, but only on non short-circuited antennae like loops with tuners and dipoles and such (I don't know what's up and down here though :) )


What is the point of the ground-wire though, if not to re-direct static into the soil?
I thought that was its purpose (Besides lightning-protection, if the antenna is placed up high in the air, which mine is not), so that part confuses me.

And also, why does the ground-wire lower the noise-floor and enhance the SNR so dramatically, if it isn't leading the static away from the radio?
I understand it must be part of the antenna, since it is connected electrically to it, I'm just not fully understanding why this setup does what it does (That's the fun of being an amature I suppose :) )

From the end of the coax, the connection from the center-connector goes through the 100 meter loop and back to the shield on the coax, where the 25 meter long ground-wire then continues around the garden and 30 cm into the soil.
That's how the electrical connection is in physical terms.
And from the coax to the radio it's just coax of course.

Perhaps I should just stick to indoors antennae or get a commercially made one, because I obviously don't like the idea of risking the radio by not having enough practical knowledge about DIY outdoor antenna-setups :)

Thanks for your input on this, and sorry for being a complete amature here :)

Re: Static shock while connecting ground-wire to radio?

Posted: Tue Mar 03, 2020 3:05 pm
by VE3EAR
Hi Jacob....I looked at the device you provided the link to and it appears to be just what you need to protect your receiver.
I understand your reluctance to build your own, so purchasing one is the option for you.

The two units I built used the toroid cores removed from computer SMPS and about 5 feet of a twisted pair of #22 gauge telephone wire. I put one end of the pair in my vice and the other end in my drill's chuck, then spun it to get about 3-4 twists per inch. I then wound that onto the toroid core until I had covered all of the core.

The pair was wound with two different colours of wire, so I connected the red wire to the antenna and the green wire to the receiver, using appropriate jacks/plugs. If you put it in a box, it must be a plastic box, otherwise you defeat the purpose!
I've used mine from well below the AM broadcast band right through to the 10M ham band.

73, Bruce, VE3EAR

Re: Static shock while connecting ground-wire to radio?

Posted: Tue Mar 03, 2020 4:11 pm
by JEL
Thank you very much Bruce :)

I will order the commercial one, just to be on the safe side (Being in Europe and not near any shops with personnel having expertise in this area of all things amature-radio, I would not feel too sure I was doing things correctly if I attempted to build it myself)

Anyway, I have been hunting some more with the multi-meter today... and discovered what I think is somewhat of an oddity.

I mentioned a few posts back that a multi-meter gave an indication of AC-currents being present in the antenna.

It turns out those readings do not actually come from the antenna, but from an unknown source in the house.

I tested all the outside antenna cables and wires and could not get any indication of AC-currents or even any significant voltage-readings (They showed up as zero in all the various combinations I tried; like center to ground, center to shield and so on)

I made a video of the multi-meter readings I got (Only on the inside, since I got no readings on the outside)
https://www.youtube.com/watch?v=e1rHhQ9O6bY

And the antenna-plug sits right next to the window, apparently close enough to fool me into thinking the multi-meter readings came from it when they in fact comes from somewhere else.

I have no idea what is happening here, but at least the antenna is not the problem I thought it was :) (I will still get the insulator though, because the jolt I felt did come from touching the antenna-wires and I don't suspect it could be a result of whatever causes this AC-current indication on the multi-meter. If it could somehow jump from the window into the antenna-cable I guess I would have also had a reading on the outside part of the antenna-cable, where I had no readings)

I think this may be a case for Miss Marple, because I'm just scratching my head at the moment trying to make sense of this :D

Re: Static shock while connecting ground-wire to radio?

Posted: Wed Mar 04, 2020 8:52 pm
by hotpaw2
Any insulated antenna can accumulate a static charge (from the wind, etc.). Just like rubbing your shoes on the carpet on a dry day can generate up to a few kiloVolts. Something like a 1 megOhm resistor from the antenna or antenna feed line to ground will help bleed off the voltage before it can build up.

I always touch any (non power supply) wire to ground (or grounded case) before connecting it to any electrical equipment, such as a radio, to bleed off any static charge. Not only antenna feeds, but mic and headset cables, scope probes, and etc. No telling who rubbed their shoes on the carpet or was petting the cat beforehand.