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Topic Title: Ham radio grounding,pme system
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Created On: 08 June 2018 01:31 PM
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 10 June 2018 09:14 PM
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MrPaul

Posts: 13
Joined: 08 June 2018

Sorry Kelly,right I have just tried a different multi meter on the plug.when I out the prongs on the earth and negative it does nothing on the meter.is that right?
Regards
 10 June 2018 10:05 PM
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jonny705

Posts: 223
Joined: 26 September 2015

Just read this thread and no nothing about Ham radio myself but....

When I was still at school a neighbour had all these massive aerials around his house and I was always fascinated what they were for- I used to see the man, but he was Scottish and always seemed to be quite angry when he spoke
But one day got the courage to ask him and he invited me in to his, to me laboratory.

He had loads of electronic things scattered everywhere , cans of oil with wires coming out of them radios resistors on the floor soldering irons he reminded me of 'Doc" Brown the mad professor from back to the future.

He also had walls littered with post cards from people from all areas of the globe all friends he tuned into when the time /space /stars were in alignment - it wasn't easy.

Ricky became a lifelong friend and probably got me into electrical stuff as would show me his exam notes and I would take them home and read them -when I done my 2360 I knew a lot more than most there because of him.

I also realised you were pretty clever to pass ham course - I could not believe how hard it was.
It took enthusiasm, effort and an element of luck to speak to a lot of people he knew.

I also know another clever guy (avionics engineer) who has a transcript on compact cassette of when he spoke ( I think) to the Apollo astronauts, - I was not sure if he was pulling my leg ,but don't think so as looked it up and how cool is that ?

And if the satellite's /internet went down via whatever reason it's the one thing that will still work - try 'Skypin' then
 11 June 2018 12:49 AM
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mapj1

Posts: 11252
Joined: 22 July 2004

Hi Mr Paul,
Sorry Kelly,right I have just tried a different multi meter on the plug.when I out the prongs on the earth and negative it does nothing on the meter.is that right?
Regards

I suspect kelly has gone to bed, it may amuse you, but, I made that assumption too - thinking it was a Mr Kelly, not Kelly as the forename, I mean . To assume, making an ASS out of U and ME and all that.
But yes, you have showed that the output of your power supply is floating, that is to say is not connected to the mains earth directly, so no large current will flow if you leave your radio connected to a local earth rod a few volts different from the mains one.
As you don't seem that confident, I can assure you it will be OK like that, just take care not to bring earthed mains stuff near it, and unplug when not in use - though that is a good idea for anything with external wiring, ham radio or not.

If you still think you are getting mains born interference, you could try running off a battery and killing the mains to all or parts of the house and seeing if the noise floor drops. It may indicate you have more sensitivity to gain by adding filtering if there is some noisy kit in the building.
And, if you get stuck, please ask, it is far safer that way. I assume you are either only a listener for now, or setting up station for the first time, is that correct ?

-------------------------
regards Mike
 11 June 2018 01:05 AM
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mapj1

Posts: 11252
Joined: 22 July 2004

jonny705, sounds like you met a hardcore enthusiast - there are quite a few like this, but equally plenty who are a bit less home brew from first principles, and enjoy the social natter aspect..
Dont do yourself down, it's not that hard to get started on low power with the foundation licence, which gets you allowed on air with restrictions, or to use anyone else's (full power or home made) rig so long as they themselves have a full licence and are supervising. There is info on foundation licence here
I'd hope most sparks could do the safety bit with a bit of thought, it's the mugging up on the permitted bands, and legal limits etc that needs more revision, as it just has to be remembered. It is aimed at normal folk, with reasonable capabilities and some dedication, nothing superhuman. A few youngsters of scout age have passed the foundation for example.

mock entry level exams

Always fun for those of us who have a ticket already to try the tests, and realise what we have forgotten, or the rules have changed.
Then there are the intermediate and full licences, that are rather more challenging, but allow more freedom to experiment. Of course, like driving, it is after the pass the real learning begins.

-------------------------
regards Mike
 11 June 2018 06:45 AM
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MrPaul

Posts: 13
Joined: 08 June 2018

Hi there,yes I just listen I enjoy it.I like to receive all kinds of transmissions,its nice to know now that it's OK to have the receiver grounded now.its made a lot of difference on the low frequency's no more horrible mains noise.thanks to everyone for your help.
 11 June 2018 01:04 PM
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MrPaul

Posts: 13
Joined: 08 June 2018

Hi again,I just want to know if this is safe to do confusing.some say no dont do it some say its ok?? How can I check with a multi meter and what should it read?when I connect the multi meter prongs to the earth and negative and set the meter to resistance I get no reading on the meter.sorry to go on but I don't want to be in danger.
Regards
 11 June 2018 04:49 PM
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mapj1

Posts: 11252
Joined: 22 July 2004

It is not completely without risk, but the biggest risk by far is bringing in an antenna feeder cable from outside, and then not grounding the system correctly, as you had before.

Now you have earthed it, the residual risk is of the PME earth, i.e. all your 'mains earth' equipment, not being at quite the same voltage as the 'terra-firma earth' outside (the radio earth).

If there had been a direct connection between mains earth and radio earth at the power supply, then there would be a risk of a large diverted current, either setting fire to the mains cable, which is unlikely, or damaging the radio, more commonly, so an isolating supply, as you have, is preferred.

But, then the two earthing systems may be some voltage apart, and under serious,and mercifully rare, fault conditions, that voltage difference may become enough perhaps to give a dangerous shock.

Now, every metal lamp-post in your street will also be at the mains PME earth potential, so the risk is comparable to leaning on a lamp-post with your feet on the grass verge, and the available stats put this as a risk of about once in a thousand years, per substation, or a few hundred instances up and down the whole UK every year, and to be fair to the DNOs, mostly issues are found and fixed very quickly.

This level of risk compares very favourably with crossing the road, or driving (both thousands of deaths, tens of thousands of hospitalisations per year.).

Of course the risk is not quite zero, but what risk level are you prepared to accept ? those who ride a motorbike as a hobby take on a far greater risk.
And as a point of note many of those who plug a car into the mains to charge it take the same risk too, and probably don't realise it.

HSL report on the safety of charging cars from PME networks (dropbox link, ignore the adverts, you don't need to join) has some figures.

-------------------------
regards Mike
 11 June 2018 06:11 PM
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kellyselectric

Posts: 361
Joined: 22 July 2016

Hi guys yes I had gone to bed but have just read all the comments maybe I should use my full name that would get rid of the confusion just so you know its Kelly-Jayne im not going to change my profile but added it here for completness
 11 June 2018 06:21 PM
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AJJewsbury

Posts: 17180
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HSL report on the safety of charging cars from PME networks (dropbox link, ignore the adverts, you don't need to join) has some figures.

Thanks for that Mike - an interesting read. Odd they didn't seem to consider the likelihood of RCD failure when comparing with TT - I thought that some basic stats on that were pretty widely available and likely more significant than consumer's earth rods rotting away. I'm not sure they're not confused DNO consumers (which presumably included commercial and industrial as well as domestic) with residential properties at one point - although the difference to the final numbers isn't likely to be too significant.

- Andy.
 11 June 2018 09:04 PM
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jonny705

Posts: 223
Joined: 26 September 2015

Well Mike I just tried one of those exams and got 9 out of 26 wrong ,but in my defense there were about things that are unique to radio such as frequency questions, the local place to me is only i.6 miles away so I might puchbike it up at the next meeting and see what it is all about.

My friend Ricky sadly passed away , a couple of years back , but it might be a nice homage to him to get into it as he was the catalyst for my interest in electrical stuff really.
Also last year when i did all the PIR's on the caravan site there was a guy there into it , and i was asking all about it as the equipment looked quite different to what i remember to say the least- he also had a man cave out back full of electronic goodies - it must be in the blood
 12 June 2018 12:34 PM
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MrPaul

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Hi there all,how can I test the power supply to see if its safe to use with a grounded radio?
Regards
 12 June 2018 01:35 PM
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AJJewsbury

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Hi there all,how can I test the power supply to see if its safe to use with a grounded radio?

Basically you're trying to show that the ELV (e.g. 12V) side is isolated from the mains earth. You can do that in a couple of ways...

1. With the PSU unplugged from both the mains and the rig; and the multimeter on a low-resistance/continuity range check between the supply earth pin and the ELV 0V (or -ve) output - an open circuit confirms they're not connected. (But do check the meter & its leads by shorting the probes together to verify that you do get a low reading - thus proving a non-reading isn't due to the correct range not being selected or a multimeter lead not being plugged in properly).

2.. Alternatively plug the PSU into the mains but keep its output completely isolated from the radio equipment and then with the meter on a low voltage d.c. range (e.g. 0-20V if you have a 12V system) measure the voltage between each output and the supply earth - if both show 0V (or thereabouts) the output is again isolated from the supply earth. Again it's worth checking the meter - it should show 12V (or whatever you expect) between the + and - outputs.

But as others have pointed out above, while an isolated power supply avoids some of the most serious safety hazards - it can't alone provide complete safety. Please do make sure you understand the remaining hazards so you can appreciate how to avoid them becoming dangerous.
- Andy.
 12 June 2018 02:22 PM
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MrPaul

Posts: 13
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Hi there, if I set it to continuity on the meter and touch the prongs together I get a beep on the meter.if put one on the plug earth and one on the negative I get no bleep on the meter.
Regards
 12 June 2018 03:14 PM
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kellyselectric

Posts: 361
Joined: 22 July 2016

Hi Mrpaul do exactly as it says on thelast post above yours and your know for sure basically 1 meter probe to plug earth other one to PSU negative if theres no beep then its isolated as most of them are please read the post above your last follow the instructions carefully and slowly youll get it get it sorted honestly just follow the instructions
 13 June 2018 10:56 AM
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AJJewsbury

Posts: 17180
Joined: 13 August 2003

Personally I'd want a definite reading (or not) displayed rather than just relying on the bleep - it depends on the meter of course, but the bleep might have a particular threshold (on my old MM I think it's below 2k Ohms - but yours might differ) - you wouldn't want to come to the opposite conclusion just because the connection was there but had a resistance a fraction above the threshold. (I would have hoped for either a solid link -ve to PE, or completely isolated, but designs vary and there might be a higher resistance). Likewise if you don't get a reading on a low Ohms scale, try again on a higher range, just to be sure. The second option (voltage test) might be a bit more robust in that respect.

- Andy.
 13 June 2018 04:10 PM
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davezawadi

Posts: 4172
Joined: 26 June 2002

If you have an inverted L type antenna and no earth connection then no wonder you have a lot of noise pickup. Any risk can be largely removed by using a reasonable size of capacitor in series with your earth connection wire, for example a 0.1uF capacitor has a reactance of about 32k ohms at 50Hz, limiting the possible shock current to a very safe level whatever happens to the PME earth potential. It will not affect the RF signal frequencies significantly. A 400V working capacitor (or so) will not fail under fault conditions. The connection to the earth rod and incoming wire should be fully insulated.

G8FNR

-------------------------
David
BSc CEng MIET
david@ZawadiSoundAndLighting.co.uk
 13 June 2018 04:33 PM
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mapj1

Posts: 11252
Joined: 22 July 2004

If you are going to isolate antennas capacitively you need to do both aerial and earth, and as you have a floating DC supply, there should be a static bleed path, perhaps a few hundred k or a meg in shunt with the cap, if not there is nothing to stop it charging up to many hundreds of volts until the capacitor pops. If I were to do this, I'd put the caps and bleed, or bleeds, in a plastic box.

This technique is not really very suitable for those intending to transmit significant amounts of RF.

The cap should be designed for 'Y' service against mains - a randomly chosen 400VDC ceramic capacitor may not be enough, but a polyester or polypropylene one rated as class Y is actually intended to hold off mains and expects to be used in a place where a short could be dangerous.

In comparison a Class-X capacitor, is an "across the line " - the capacitor placed between phase and neutral - fails because of an overvoltage event, it is allowed to fail short. This failure, in turn, should cause a fuse or circuit breaker, to open. Therefore, a capacitor failing in this fashion between L-N, would not cause any electrical shock hazards, if it failed clear short or open.

A Class-Y capacitor, is intended for use as "line to ground" - if that capacitor fails short, this could lead to a fatal electric shock due to high voltage on the ground connection. Class-Y safety capacitors have a deliberate weak link, like a fuse, and are therefore designed to fail to an open state. usually at least.

-------------------------
regards Mike


Edited: 13 June 2018 at 04:55 PM by mapj1
 13 June 2018 09:37 PM
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AncientMariner

Posts: 861
Joined: 14 December 2004

Mike
Q6 on the mock exam. Any idea why 431.0 - 432.0 MHz is not allowed within 100km of Charing Cross?

From the RSGB map https://www.thersgb.org/services/licence-map/charing-cross.htm it covers out to Oxford, Cambridge and almost out to the south-east coast.

A nice round number too, in the days of miles, 62.1371 miles would have been too precise!
73s

Clive

-------------------------
Clive S Carver GCGI IEng MIET MITP
 13 June 2018 10:10 PM
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AncientMariner

Posts: 861
Joined: 14 December 2004

Ah.......

Well, in my GW8AOC days, I would have guessed a river view from Waterloo Bridge House, the then home of the Ministry of Posts and Telecommunications.

But guess that the current interest group may be nearer Vauxhall Bridge?

Back to G8AOC, xtal controlled AM 2m rig with a Mullard QQV03-20A tripler to give me a few watts on 432.108 MHz into a J-Beam antenna.

73s
Clive

-------------------------
Clive S Carver GCGI IEng MIET MITP
 14 June 2018 11:26 AM
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MrPaul

Posts: 13
Joined: 08 June 2018

Hi all again,would it be ok to just ground the braid on the back of the antenna connection and not ground the radio?I can strip the case off the coaxial cable and solder the ground wire to the braid.
Regards
IET » Wiring and the regulations » Ham radio grounding,pme system

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