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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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5th Jul 2020, 11:01 am | #21 |
Pentode
Join Date: May 2011
Location: Enniskillen, Fermanagh, UK.
Posts: 188
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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. Cliff. |
5th Jul 2020, 11:09 am | #22 | |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,340
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Re: Static on antennas
Quote:
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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5th Jul 2020, 2:55 pm | #23 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 693
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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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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
5th Jul 2020, 9:07 pm | #24 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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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 |
5th Jul 2020, 11:43 pm | #25 |
Nonode
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 2,181
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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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6th Jul 2020, 9:15 am | #26 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 693
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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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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
7th Jul 2020, 5:30 am | #27 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,894
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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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Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
7th Jul 2020, 9:34 am | #28 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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Re: Static on antennas
Thanks
Mike |
12th Jul 2020, 10:50 am | #29 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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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 |
12th Jul 2020, 3:42 pm | #30 |
Guest
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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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12th Jul 2020, 4:31 pm | #31 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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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 |
12th Jul 2020, 7:43 pm | #32 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,687
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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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Regds, Russell W. B. G4YLI. |
13th Jul 2020, 7:11 am | #33 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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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 |
13th Jul 2020, 9:03 am | #34 |
Octode
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,765
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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 |
13th Jul 2020, 9:36 am | #35 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,273
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Re: Static on antennas
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Kevin |
13th Jul 2020, 11:43 am | #36 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
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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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14th Jul 2020, 12:42 pm | #37 | |
Heptode
Join Date: May 2014
Location: Salisbury, Wiltshire, UK.
Posts: 998
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Re: Static on antennas
Quote:
D
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David, G4YVM. |
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