Ground Spike necessary ?

Everything Ham Radio in here, Frequencies, Equipment, Repairs, Mods, Licensing and More

Re: Ground Spike necessary ?

Postby lars » Tue Mar 28, 2017 9:03 am

A digression, really, but --

About thirty years ago there was a fashionable theory that a properly-shaped lightning rod had a deterrent effect on lightning strikes. This was (apparently) due to poorly-defined "ion streams" in the air above the rod, when in the vicinity of a charged cloud. Only (apparently) well-earthed and properly shaped conductors had this effect, which is why standing with your golf club in the air in the middle of a field during a storm still isn't a good idea.

I don't know if this theory has much traction these days; but it remains the case that the mechanism of lightening strikes is not at all well understood, so it seems to me that it's at least possible that something of this sort goes on. If true, it might explain why tall radio masts are struck by lightening less often than might be expected.
lars
 
Posts: 142
Joined: Fri Jun 10, 2016 9:03 am

Re: Ground Spike necessary ?

Postby ur5by9 » Tue Mar 28, 2017 10:14 pm

This topic does make for an interesting read, My intentions were when setting up my shack for the first time in 2 years to look at my mast and determine if a ground spike was necessary.
then my thoughts turned to my radio equipment which all has earth tags on the rear of the radio's, This make me consider also earthing my equipment.

In all fairness living in Scotland where lightening is not a regular occurrence I was only going over a check list to run a nice clean station.
My mast antenna is only for 10m as I have a long wire doublet for the lower HF bands.
I have a separate VHF / UHF vertical at a static height, I also use this antenna for scanning.

I maybe over complicating things in anticipation to get the Shack running.
User avatar
ur5by9
 
Posts: 22
Joined: Sun Mar 05, 2017 3:53 pm
Location: Nr Edinburgh

Re: Ground Spike necessary ?

Postby G4RMT » Wed Mar 29, 2017 7:27 am

Perhaps we should all consider this more than we do. One colleague of mine is only interested in one thing - his house. If he loses the equipment, he is insured, but the house, despite being insured, is his home and he does not want to have to move and start again - which most big fires usually mean.

His fear is that the external metalwork creates a path into his house, and once there, it does the damage. Joining all the grounds together makes the access even better.

In audio and video entertainment where I work, ground loops are one of our big problems. PA systems hum and the big video walls have hum bars running up and down them when people ground things randomly to 'ensure safety'.

At events, festivals and theatres we had a long term problem with the front of house mixers - if they derived their power locally, from a handy socket, very often terrible hum was the result. The earth in the audience and the earth on stage were many metres apart, and both a different reference voltage - sometimes you'd have more than 5v difference, and this 50Hz voltage would 'leak' into the sensitive audio kit and huge hums were the result. The solution was to run a very long cable from stage to the back so the audio system all got it's power and grounding from the same place. Now it's not a problem anymore because we have a fibre optic cable doing the job, but for years this has been a real pain. Worse - unskilled people would remove the earth wire from the plug, to cure the problem. Then things would go wrong and microphones would become live - nasty.

We started with lightning, but the problems of grounding in the shack are the same - multiple earths can cause unintentional problems.
G4RMT
 
Posts: 1105
Joined: Sat Feb 07, 2015 5:45 pm

Re: Ground Spike necessary ?

Postby ur5by9 » Wed Mar 29, 2017 11:24 am

Interesting way to describe this and one which I understand :)

Back in the 90's I also worked on Sound and Light and also encountered the issues your explained.

The lighting mas mostly Martin varieties Mac 500's and 1220 scanners DMX control using a masterpiece, Audio was MC2 Amplifiers and ATC drivers as it was more a club environment
the mixers were generally cloud and a set up of Technics turntables.

Non the less my gained experience in the field lets get understand your explanation of earthing systems.
User avatar
ur5by9
 
Posts: 22
Joined: Sun Mar 05, 2017 3:53 pm
Location: Nr Edinburgh

Re: Ground Spike necessary ?

Postby lars » Wed Mar 29, 2017 12:20 pm

My experience is that, in the audio world, safety earthing and performance-related earthing are often in opposition. I guess this has become less of a problem with increased use of digital transmission, but with long analogue signal runs it used to be a total bear. Back in my student days, one of my class-mates died -- literally died -- on stage, because some dickhead had disconnected the safety earth from a microphone amplifier.

Earthing for safety is pretty straightforward, at least in principle -- just earth the hell out of everything. But so far as performance is concerned, I've never found earthing to be anything other than a black art. The principles we studied in elec. eng. classes never seemed to apply in any rational way, and ever minor changes could have huge, inexplicable effects. My limited experience with RF has been much the same. I'm not convinced that anybody really understands RF earthing -- even the ARRL handbook has vague and conflicting advice.

In the end, I think we have to be safe. I've learned the hard way -- but not as hard as some -- that compromising safety earthing for the sake of performance is a stupid idea.
lars
 
Posts: 142
Joined: Fri Jun 10, 2016 9:03 am

Re: Ground Spike necessary ?

Postby m0lsx » Wed Mar 29, 2017 1:01 pm

lars wrote: I'm not convinced that anybody really understands RF earthing -- even the ARRL handbook has vague and conflicting advice. .


It is certainly something of a black art, in part due to the fact that there are so many variables.
Buy a database from Kimmy JS19 via http://ukscanningdirectory.co.uk/
Or do Google search of this forum via https://www.google.com/cse/home?cx=partner-pub-6291336405621919:2662881632
73 De Alan (M0LSX.)
http://www.qrz.com/db/M0LSX"
User avatar
m0lsx
 
Posts: 5368
Joined: Wed Nov 21, 2012 9:14 pm
Location: Norwich. TG21.

Re: Ground Spike necessary ?

Postby G4RMT » Wed Mar 29, 2017 9:09 pm

Indeed - only recently we explained to somebody that a dead short on the meter on the aerial terminal does not mean the aerial is fault. I've always found the notion that RF can work into a dead short extremely difficult to quantify' Logic just fails here. RF is AC current, so a short should be a short until in inductance and capacitance get in the way!
G4RMT
 
Posts: 1105
Joined: Sat Feb 07, 2015 5:45 pm

Previous

Return to Amateur Radio

Who is online

Users browsing this forum: Google [Bot] and 0 guests