Radio LoRa Antenna lightning/surge protection.

[jurajpe]

Hi. I started to use a Helium miner, effectively a raspberry pi small system that does what it does and connects to: EU868 frequency lora 3dbi 50ohm antenna. Also it has wifi/ethernet and of course power. Small box consuming about 15w.
Usually these come with a small antenna that is meant to be inside. However to increase the performance one can place the lora radio antenna outside. I want to do exactly that. I would like to kindly ask a couple of questions:
1. Is lightning protection of the antenna and bracket needed? I am in the UK london and I know that not all buildings need lightning protection. So I scrapped that. There is a large church near by and many other higher objects more likely to be struck.
2. My antenna will be at the eaves height of a house. I have no access to get it any higher. I want the bracket to be plastic/glass fibre.
3. I am slightly worried about the static buildup only really. I cannot access a ground wire. There is none on the facade. However all pipes (water/gas) inside and outside are grounded.
I want to fit a arrestor like this one:
https://www.ebay.co.uk/itm/400W-Coa...2349624.m46890.l49286&mkrid=710-127635-2958-0
but not sure where along the antenna cable. As the cable enters the building? Or inside? And where can I ground it? Can I open a socket and wire it to there for example to a existing internal grounding loop?
I want to call a electrician to do this but those I spoke to were not familiar with the antenna issues. thank you for any advice

 

[RandomGrinch]

Do not connect it to an electrical socket!
Here are some example installation instructions for a GPS antenna and arrestor. Note the section for grounding recommendations. Ideally you need a separate, dedicated and external route to ground (if the electrical equipment connected to the aerial is class 1 it should be bonded to the same earth - probably not relevant to an RPi).
But, there are plenty of TV aerials around without this sort of dedicated protection, so you may be over thinking!

 

[ericmark]

I went to a lecture on this, it is of interest to every radio ham. A lighting strike is going to take out equipment, there is no way to protect, so step one is to reduce the likely hood of a lighting strike, so do not mount on sharp corners like gable ends, or on soot lined chimneys, which is where most aerials are mounted. And do not earth.

The DTi did a book "How to improve Television and Radio reception" now out of print, but they did publish the plans for a braid breaker that would allow TV signals to pass but not DC so you will not get a belt from aerial but neither is it held at ground polarity so does not attract lighting.

Most radio rallies would have the kits of parts for sale, but this was a long time ago.

However TV plates do come in two types, internal which allows DC to pass to power digi eyes or mast head amplifiers, and those with capacitors in for use to aerials that have capacitors in.

Since a thunder storm often includes wind, lighting often hits the ground near some thing high.

It is a long time ago when I studied for my RAE, and the TV is clearly receive only, I know we used an array of large resistors and a spark gap, but the main idea was to disconnect the radio in a storm and the resistors was so you did not get a shock reconnecting after. With satellite dishes they can be mounted much lower, half way down the wall, so unlikely to get hit.

And that is what I would do, I would mount aerial a little lower maybe in the loft space, if worried about lighting strikes. I have lost a video recorder due to near miss, but it protected my TV.

I only now use hand held radios, so not worried about lighting strikes, when in Hong Kong I made an aerial from 300Ω ribbon cables in the form of a slim jim, and selotaped it to the window, that was OK at 30 watt, would not want to go much higher.

I think you are limited to 10 mW on the 863.0 - 865.0 MHz band, although for some uses allowed up to 500 mW, I have not read the EU868 spec, but with many of the licence free devices you are not permitted to make your own equipment. And there are rules to stop you increasing the distance covered, also I found for my VSWR meter to work I needed at least 1 watt, so making your own aerial is a bit of guess work.

Aerials are odd in the way they work, the rubber duck as the CB people called it, at PMR 466 frequency can be changed by using silicon sealant to glue on the end, I found if I cut a little too much off, extra silicon sealant would get it back to spec, and most of the meters I used would not reach 868 Mhz.

But the aerial is so small I think rather unlikely to be affected by an electric storm in the UK, but best place to find out info is your local radio club, every club seems to have some one who is a fount of knowledge.

 

[RandomGrinch]

Really interesting post @ericmarc, I didn't know about the silicon sealant. It reminded me of the many times I have seen people chewing on the end of their handheld CB aerials. I'm now wondering how that affected signal attenuation!
And a friend of mine has this small antenna in their back garden!

I've been meaning to have a chat about it..

 

[jurajpe]

Thank you for your replies. Yes I might be overthinking. The only thing I can really do is to instal the arrestor and ground it. But I have no access to a ground loop, pit externally. Yes the power is limited to the antenna. I will check it and compare to your post. For now I will leave it. I will install the antenna just under the eaves. I found a surge protector that does not require ground wire, and should be used as a additional protection means, so I use that and let it be. I am fully aware what the ideal setup should be and also that the risk in london in particular is slim. But as I have no access to the facade and ground on that side of the house it is kind of futile. But I very much apreciate your inputs!!!

 

[JohnW2]

1. Is lightning protection of the antenna and bracket needed? I am in the UK london and I know that not all buildings need lightning protection. ....
2. My antenna will be at the eaves height of a house. I have no access to get it any higher. ...

Thank you for your replies. Yes I might be overthinking. ....

Yes, I would say that you are 'overthinking'. As has been implied, the 'need' for lightning protection is probably less than exists for the countless (undoubtedly millions) of domestic TV aerials, given that many/most of them are higher and more potentially exposed to lightning than you propose - and it is exceedingly rare for any of them to have any sort of explicit protection against lightning.

Kind Regards, John

 

[bernardgreen]

Protecting equipment from damage by lightning strikes is a black art

Read more: https://www.diynot.com/diy/threads/lightning-keeps-wiping-our-router-and-phone.526414/#ixzz757cehVIu

 

[FrodoOne]

Hi. I started to use a Helium miner, effectively a raspberry pi small system that does what it does and connects to: EU868 frequency lora 3dbi 50ohm antenna. Also it has wifi/ethernet and of course power. Small box consuming about 15w.
Usually these come with a small antenna that is meant to be inside. However to increase the performance one can place the lora radio antenna outside. I want to do exactly that. I would like to kindly ask a couple of questions:
1. Is lightning protection of the antenna and bracket needed? I am in the UK london and I know that not all buildings need lightning protection. So I scrapped that. There is a large church near by and many other higher objects more likely to be struck.
2. My antenna will be at the eaves height of a house. I have no access to get it any higher. I want the bracket to be plastic/glass fibre.
3. I am slightly worried about the static buildup only really. I cannot access a ground wire. There is none on the facade. However all pipes (water/gas) inside and outside are grounded.
I want to fit a arrestor like this one:
https://www.ebay.co.uk/itm/400W-Coa...2349624.m46890.l49286&mkrid=710-127635-2958-0
but not sure where along the antenna cable. As the cable enters the building? Or inside? And where can I ground it? Can I open a socket and wire it to there for example to a existing internal grounding loop?
I want to call a electrician to do this but those I spoke to were not familiar with the antenna issues. thank you for any advice

Without an over-building (sort of Faraday Cage) you CANNOT protect from any lightning strike.
However, you may be able to protect from "Static Buildup".

The device to which you have referred looks like a more expensive version of a "Grounding Block", such as are required in the USA on their Antennae Installations. (https://us-browse.startpage.com/av/...d635b24e1b092a5d28227fda2425098ca6dcd0ed237c1)

These are readily available, including those on https://www.ebay.co.uk/sch/i.html?_...0.l1313&_nkw=antenna+grounding+block&_sacat=0 many of which seem to be quite overpriced on that site.

 

[bernardgreen]

Usually these come with a small antenna that is meant to be inside. However to increase the performance one can place the lora radio antenna outside. I want to do exactly that.

Are you sure that the extra gain of the LoRa antenna will not raise the ERP ( Effective Radiated Power ) of the transmitter to a level above the maximum permitted EPR

Page 16 of https://www.ofcom.org.uk/__data/assets/pdf_file/0028/84970/ir-2030.pdf

IR2030/1/15
Non-specific short-range devices 868 – 869.7 MHz
Maximum transmit power / Power spectral density / Field strength 25 mW e.r.p
Duty cycle TX On-Off <0.1%