Protection agains lightning strikes

Useful information regarding antennas for SDR products.
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Fabian_Pruitt
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Joined: Mon Jun 17, 2019 8:30 am

Protection agains lightning strikes

Post by Fabian_Pruitt » Mon Jun 17, 2019 9:00 am

Hi
As a complete newcomer to SDR, I started with a 'Nooelec' dongle with one of those tiny 6in whip antennas which did nothing to bring in any signals what so ever. Just got a load of varying static and pretty graphics. Not to be put off by this I bought an SDRPlay RSP1A and a Discone antenna. I intend to mount this on a 20ft pole on the side of my bungalow but am unsure about what I should do about lightning strikes.

Are there any forum members who have erected one of these antennas and what did they do to protect it against lightning. I don't want to go through the trouble of erecting the Ariel only to find I should have added a length of copper cable to the top of it or added anti lightning gadget between the end of the coax cable and the RSP1A.

I'm fully committed to continuing with this hobby so I've joined the RSGB and made inquiries about taking the 'Foundation' exam in the near future. I'd like to get the RSP1A set up as soon as possible so I can get a better idea of what I need to know before going in for the exam.

Any help here would be great.

Thanks a lot.

Michael.
(Fabian_Pruitt)
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Michael
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glovisol
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Location: Piedmont, Italy

Re: Protection agains lightning strikes

Post by glovisol » Mon Jun 17, 2019 6:48 pm

Hi Michael,

You can get an idea about my experience with a Discone antenna here:

https://www.sdrplay.com/community/viewt ... f=8&t=4109

As far as my experience goes, for low noise recepton it is best to leave the antenna floating: you connct a coaxial cable to the antenna and you go to a metal box anywhere along the coaxial cable path. Inside the box you connect a choke between the coaxial cable inner and the shield. This choke will effectively short circuit the cable for lightning or other transients. You also connect another choke from the coax cable shield and a good ground (stake, water pipe?). In this way you will discharge static transients to ground but you will not allow ground to bring noise to the receiver.

glovisol

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JJ_in_TN
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Re: Protection agains lightning strikes

Post by JJ_in_TN » Mon Jun 17, 2019 7:07 pm

You have asked for help on an immense topic. Ham radio operators have been grappling with that question for decades.
For starters there are many, many good resources you could familiarize yourself with, such as http://www.arrl.org/lightning-protection or https://www.polyphaser.com/.

How much money and effort are you willing to expend to reach what you consider "adequate" protection? If you have an antenna that is quite a bit lower than surrounding structures connected to an RSP-1A you may not want to worry about it. Mitigation may cost more than the equipment you are protecting. Glovisol has some good suggestions for dealing with transients and static.

In the event of an actual direct strike, assess the damage and file for the insurance.

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Fabian_Pruitt
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Re: Protection agains lightning strikes

Post by Fabian_Pruitt » Mon Jun 17, 2019 9:23 pm

Firstly, thank you both for taking the time to reply. I must confess this is my first venture into the world of radio and at 73 I've left it a bit late. But I am a computer user and was fascinated when I came across the videos about the SDRPlay. I must admit I posted this request in haste because I've come to realise that I already have 2 ariels up on my roof and they haven't been hit by lightning in 20yrs. So what's the chances of my Discone antenna going the same way. Hardly any I should think.

I'll print out both your replies and I'll have a look at that other article glovisol which looks very interesting. I'll look into this further and think about setting up a choke in the coax as you suggested.

Thanks again for the posts.
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Michael
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Mike2459
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Re: Protection agains lightning strikes

Post by Mike2459 » Tue Jun 18, 2019 12:52 am

Here in the US home antenna installations are covered under Article 810 of the National Electric Code. It specifies that antenna masts be grounded and coaxial cable shields be grounded to the electrical system ground. It specifies the use of antenna discharge units (Polyphasers) in antenna leadins.

https://www.ecmweb.com/code-basics/arti ... -equipment

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Fabian_Pruitt
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Re: Protection agains lightning strikes

Post by Fabian_Pruitt » Tue Jun 18, 2019 8:49 am

Hi Mike
I read the article 810 about grounding your antenna which I found interesting. A friend who's been a radio operator for 40yrs said the 810 article was well over the top and not to pay too much attention to it because we ground our antenna masts as a matter of course here in the Uk. It isn't so much a law here as common sense practise. I'm only relating what he told me as I'm the new guy on the block and find this subject somewhat overwhelming.

As I said in a previous post, I have two aerials (TV) on my roof which aren't grounded in any way as do every house in the country. But I've never heard of lightning striking any of them. certainly not in my lifetime anyway. Perhaps it's somewhat nieve of me, but any time a storm was forecast I'd uncouple the coax connector and secure it outside along with the Ariel mast so it was completely separated from the house.

I do appreciate members taking time to explain all these precautions and procedures when setting up masts and Ariels and hope they're not offended by my somewhat negative outlook regarding this information. I hope to learn all these features of our hobby over the coming months.

Thanks again for your help.

Michael
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Michael
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