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Old 5th Jul 2020, 11:01 am   #21
Gi4CZW Cliff
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Default Re: Static on antennas

Hello Mike and all. I had an issue with lightening and find this thread interesting.
Five IRF520's plus replacing them is a price. Flashing neon, when static high, would need you to be looking at the detector. I remember a static/lightening alarm circuit, but can't place it so far. Temp. solution is a double pole knife switch fitted near to shack door, so you throw it, on exit-entry. Do I remember the Rupert Bear strip on back page of Daily Express showing a row of Jars, a number of which would glow to indicate the strength of the static ?
stay safe.
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Old 5th Jul 2020, 11:09 am   #22
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Default Re: Static on antennas

Quote:
Originally Posted by crackle View Post
.. I have shown the resistor across the bottom of the balanced feeder where it joins the coax.

So you did, it registered as being up at the other end of the feedline for some reason, must get more sleep
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Old 5th Jul 2020, 2:55 pm   #23
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Default Re: Static on antennas

The 40W output of the tranceiver corresponds to approx. 63V pk into 50 ohms. As the IRF520 is has a breakdown voltage of 100V, you should be able to find a suitable bi-directional transorb (say 80V) that will deal with lightning induced static pulse but not be activated by the transmitted output.
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Old 5th Jul 2020, 9:07 pm   #24
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Default Re: Static on antennas

Hi Keith
Is this the sort of thing https://uk.farnell.com/stmicroelectr...-r6/dp/1689205
I am confused by the different voltages, which one is the important one

Reverse Stand-Off Voltage Vrwm: 68V
Clamping Voltage Vc Max: 121V
Breakdown Voltage Min: 75.6V

Thanks
Mike
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Old 5th Jul 2020, 11:43 pm   #25
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Default Re: Static on antennas

Food for thought. Must be some modern equivalent,but the older telecomms members (GPO/po) will remember carbons on the frame to stop lightening strikes. As said- I'd expect modren electronic/digital exchanges needed something more conductive. (GDT?).Would something like this cause problems on RF as low as10/11 m.
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Old 6th Jul 2020, 9:15 am   #26
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Default Re: Static on antennas

Hi Mike,
The BZW50-68B might be marginal as it will just start to conduct at 68V (min). The TX might exceed this if loaded into something other than 50 ohms resistive. You'd probably be better off with the 82V part, albeit with slightly less protection.



There's quite a good article on TVS devices at:
https://www.google.com/url?sa=t&rct=...4ijfARBGfrTNS4


Keith
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Old 7th Jul 2020, 5:30 am   #27
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Default Re: Static on antennas

If thinking of using TVS diodes, look at their capacitance values in the data sheets. It can be a problem on RF signals. Same with ordinary zeners.

MOVs can be lower capacitance, and GDTs lowest of all.

David
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Old 7th Jul 2020, 9:34 am   #28
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Default Re: Static on antennas

Thanks
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Old 12th Jul 2020, 10:50 am   #29
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Default Re: Static on antennas

I am planning to install another deeper earth for my antennas in the garden. (8 foot if I can manage to get it that far in)

Has anyone done this and give any tips, I have purchased 2 5/8th rods, a threaded joiner and a nut to drive the first rod in with.

I have also made a 1:1 balun to connect the coax to the dipole feeder. This to me seems the best way to give a DC ground to both halves of the dipole.

I also purchased 2 lightning arresters for the 10m vertical and the dipole.
Does any one have a cut away drawing of one of these, I would be intrigued to know what was inside and how it protects from lightning. Is it in effect just a spark gap from the centre conductor to earth?
Anyway it will be a little extra comfort to have them.

Below is a plan for my new earth termination box that will be about 8m up the garden attached to the fence.
The new deep earth will be bonded to the original 4 foot earth rod I put in by the tree that the 10m vertical pole is strapped to. In the recent hot spell the ground was very dry around that short earth rod and the efficiency of it was rather suspect.

I would welcome any observations on my plan.
Thanks
Mike
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Old 12th Jul 2020, 3:42 pm   #30
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Default Re: Static on antennas

I wanted to put 7 8' ground rods in my garden and got 14 rods 7 couplers, 7 "top bits" and an SDS drill "hammery bit" (borrowed the drill proper). Rod one went in 4' no trouble, connected second rod and about 6" in it struck chalk then it took 20 minutes of SDSing to get it down. I gave up the 8' malarky and now the other 12 rods are only in 4'. I suppose I must have a fairly good earth.
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Old 12th Jul 2020, 4:31 pm   #31
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Default Re: Static on antennas

With a bit of luck I think the Essex clay may be a bit deeper than 4 foot.
I have heard of people using a hammer drill to drive the rods in. But I only have a standard drill with hammer action.

Mike
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Old 12th Jul 2020, 7:43 pm   #32
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Default Re: Static on antennas

If you're putting radials in they needn't be deep at all. The further out your rods are from each other, the deeper the ground they will penetrate and the better your earth will be. But a bit depends on the topology of what's under there.
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Old 13th Jul 2020, 7:11 am   #33
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Default Re: Static on antennas

This project is primarily to take all steps to help eliminate static spikes from entering the shack. It is believed that it is static build up that has already caused one of my rigs to blow its OP mosfets 5 times now.
I believe this is the cause because at the same time, during nearby thunder storms, we have been hearing a clicking sound coming through the TV amp and speakers. It is believed this is static building up on the dipole antenna and arcing across the first tuning capacitor of my T match tuner. The resultant very high voltage discharge to earth is probably travelling around the ring main to the MET at the fuse box. As a result of the recent extremely dry spell and my existing 4 foot earth rods having poor efficiency due to the dry ground.
I am hoping that at 8 foot down the ground will be more conductive.

Mike
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Old 13th Jul 2020, 9:03 am   #34
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Default Re: Static on antennas

I installed an 8 foot ground rod last year. I used rods and couplers etc from Screwfix, probably the same stuff you have. I also have thick clay soil.

I used a combination of 2 different driving methods, which id highly recommend:

- SDS hammer drill (the big type you can break concrete with) - You can get special attachments, but I lashed something up, (sticking a chisel point into an extra coupler I swapped out for a good one for the 2nd rod). I found this got me 70-80% of the way very quickly indeed!

- Sledge Hammer - For some reason the SDS drill stopped being effective towards the end, possibly the amount of rod in the soil served to dampen the vibrations from the drill. But driving the rest of it in with the sledge hammer was pretty easy.

All in all, I think I did it within 30 minutes in total and it was easier than I thought.

I did find the coupling starts to "untwist" as you drive the rods in, I regularly tightened it up, and also did at the end.

Best Regards
Adam
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Old 13th Jul 2020, 9:36 am   #35
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Default Re: Static on antennas

Here's Mr Carlson's video about static on aerials

https://www.youtube.com/watch?v=-_MsOjQEC3k
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Old 13th Jul 2020, 11:43 am   #36
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Default Re: Static on antennas

Interesting.

Possibly he was right about the spark at the radio being RF related, maybe caused by a flashover to ground somewhere further "up the line" in the aerial system generating damped oscillations a la spark transmitter?
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Old 14th Jul 2020, 12:42 pm   #37
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Default Re: Static on antennas

Quote:
Originally Posted by G6Tanuki View Post
In times when I've experienced static-buildup-on-antennas I've been happy to fit a low-wattage high-value *wirewound* resistor or two from the static-afflicted parts to the RF ground.

Something like 10KOhms 5 Watts.

The wirewound-ness provides a HF/VHF-choke effect, so it doesn't cause significant waste of RF power or 'RF unbalance' - and a resistor of 10K to the local RF-ground won't cause any significant risk-currents if your DNO's neutral/grounding arrangement fails so the neutral/ground 'floats' towards the supply-phase voltage.
I always thought common wisdom said NOT wirewound resistors.

D
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