Anyone care to help with grounding?

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Anyone care to help with grounding?

Postby Dave In Herts » Sun Feb 23, 2020 4:10 pm

I'm new, taking my foundation exam (UK) next week so not transmitted a watt yet but have been listening for a year on HF with home built antennas. Have recently got a transceiver and built an EFHW80-10 antenna ready for play time :)

In discussion about my setup, I was asked about my grounding arrangements and said i didn't have any :) Naturally that caused an internet flare-up and a storm of advice on what to do and not to do, resulting in much confusion and some wasted money.

Early advice was to ensure i grounded the coax sheaths at the entry to my shack (1st floor room) to an earth rod, that rod had to bonded back to the main supply panel for UK regs.

That is underway now, waiting for an electrician to do the final bonding.

Yesterday advice changed and was advised to just ground the EFHW transformer at the feed point, I tried this today, sunk a ground rod and connected the transformer up.

The result was that i had a bad earth-loop hum on the PC (connected to the radio for FT8 etc) which wiped out my reception totally, I have now disconnected that earth rod and all is normal again.

Any chance someone could please advisements what is good/bad etc ? This subject seems to be secretive or filled with bad advice and is slightly putting me off radio now!

Even the RSGB (UK controlling body) offers no advice, which i find poor to say the least.

Thanks
M7DJK
Dave In Herts
 
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Mon Feb 24, 2020 2:20 pm

Thanks , got that one plus the "advanced" one from RSGB, however if you read it, it actually offers no advice on grounding at all - it just outlines the UK regulations and different supply types we may have.

There is no definitive data or information on how, where or why to even bother earthing a ham radio setup in them.
M7DJK
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Mon Feb 24, 2020 4:31 pm

Trying to make things easier to explain, i did some sketches...

This is my setup at present, note the lack of any grounding ;)
http://testsite.davekearley.co.uk/wp-content/uploads/Shack.pdf

Yesterday I added a rod on advice given and got terrible mains hum wiping out my FT8 reception...
http://testsite.davekearley.co.uk/wp-content/uploads/Shack-humming.pdf

So after spending a whole day reading and searching i have come up with this, it *seems* to meet regs re bonding but have no idea if its any good for my radio setup...
http://testsite.davekearley.co.uk/wp-content/uploads/Shack-proposed.pdf

Any ideas before i do the work?
M7DJK
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Re: Anyone care to help with grounding?

Postby radiostationx » Mon Feb 24, 2020 9:33 pm

Good Illustrations Dave,
RF ground used to be easy, laying a fan shaped pattern of wires along the ground or driving several earthing rods into the soil and connect them with thick copper cable or burying metal plates and doing same then back to shack with some thick earth to a copper bar (usually fabbed up from a bit of busbar) mounted on brackets near to radio. All the equipment ground terminals were then attached to the copper bar with short thick copper cable links.
Like electrical earthing it was/is good to have a large rf ground (sub subterranean counterpoise) with as short as poss earth cable to shack. This was "station earth" or "station ground" or "rf ground"..Totally independent of Electrical earth.

This has changed somewhat in recent decades because of changes made in domestic earthing. Gas pipes were used as earth because they were cast iron/steel but like water pipes they have changed to plastic so supplementary earth rods were fitted in most properties.

An electrical fault from your property or a neighbouring one could cause the fault current to flow into mains earth (rod) across to the counterpoise and on to your equipment and to you.

As the electricity would in theory reach the counterpoise due to its very low resistance (potentially lower resistance than mains earth).

Elecrical Earthing values change with soil conditions, soil types some are better than others at conducting electricity etc etc .

Your spark will identify the earthing system and test it with an earth loop impedance tester. Find out from him the type of system used in your house.
(He wont be able to identify neighbours systems though)

Not many will commit to advising on RF grounding because of the minefield of potential risks.
"Well the RSGB told me to do it"...In todays blame claim world I dont think so..

You have a dilemma working from a 1st floor room. To reach ground you would have to have a run of at least 10-15ft of copper cable,Aside from the Lightning strike risk..
This would form a perfect phantom antenna. Your coaxial runs, I take it you are using screened coaxial ?
I see in your diagram that you cross bonded the coax braids at the entry point, personally I would not do that and I would leave the jackets in tact.

The 49:1 unun I would try use without a ground,the ground wire for this again would be 10-15ft I take it ?

With all those coaxials around (not unusual for a radio amateur), have you put some ferrite beads on those in the shack ? I can see your PC is in the same room... Eradication of interference can be extremely challenging but its all about experimentation and gaining/exchanging knowledge from your experiments which is what amateur radio is all about.



Well done on taking the test btw Dave..keep the faith..all will be well and as said ,very good illustrations !
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Mon Feb 24, 2020 10:56 pm

Thanks,

Our supply is PME as are the whole estate most likely, built around 1985. Ground rods must be bonded to supply earth.

As this topic is taking input from multiple sources I have created an update diagram here...
http://testsite.davekearley.co.uk/wp-content/uploads/proposed-mk3.png

There was a lot of support for grounding the coax feeds at the point they cross the house wall boundary, even some data on electrical institute sites.

Yes the EFHW will only be grounded if it works better that way, seems to be a suck-it-and-see type thing with them.

The main bonding line from shack to rod will likely resonate around 17Mhz so somewhere between 17m and 20m bands, based on 1/4w but this is guesswork as i will have to measure the cable run and calculate it to be accurate. I have a diagram that uses coax for the earth with the rod end shorted and the shack end coupled with a capacitor, this can be any length and sounds useful if i have issues.

Yes i have plenty of ferrites fitted and some spares.
M7DJK
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Re: Anyone care to help with grounding?

Postby radiostationx » Tue Feb 25, 2020 1:50 am

Hi Dave,
I understand the logic in binding the coaxials at entry but I also see it causing issues as well because you would have 4 or 5 unbalanced feedlines coming to a common point (10mm binding ) so you would have 4 or 5 braids fanned out acting as phantom antennas with the potential of picking up stray signals . This is also a pitfall of antenna combiners.
I wouldnt worry to much about what the upstairs shack to rf gnd rod cable link 1/2 wave length is..mw can be picked up on 6ft of wire which isnt exactly the perfect antenna for that band.
It is likely noise generated by local household electronics will be your biggest enemy.
Lots of experimentation for you and your station in the coming weeks and months me thinks.

Slightly off topic..Back in the day before coaxes, a lot of amateurs used 75ohm balanced line (quite hard to find now), a bit like bell wire but better ones were made from festoon lighting chord which had impedance of around 72ohms it was cloth covered and the conductors were twisted..because the conductors are equal in size the currents that flow along it are more or less exactly equal and opposite in polarity so they cancel each other out. This type of feedline gave little in the way of receive interference. This method is used in CAT 5 and CAT 6 Ethernet cables where each of the 4 the pairs have twisted conductors to combat cross talk and unwanted signal interference, they (pairs)are also foil screened to add further immunity.
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Tue Feb 25, 2020 9:02 am

Interesting, thanks.

Re the combined braids - they combine any way about 6' further along at the antenna switches and ultimately at the star ground point so does the joint at 6' distance make any change, i cant see the electrical difference here?
M7DJK
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Re: Anyone care to help with grounding?

Postby radiostationx » Tue Feb 25, 2020 9:07 pm

Sorry Dave I mis understood your diagram slightly in the area of 2/1 and 4/1 so these are antenna switches...

Have you considered an artificial ground such as MFJ one ? (not that I want to promote mfj as the build quality of their stuff is usually crap)
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Re: Anyone care to help with grounding?

Postby Dave In Herts » Tue Feb 25, 2020 9:20 pm

I did see the MFJ item but i think i'll try the real ground first :smiles:

Yes the 2:1 and 4:1 are switches, they have metal bodies and can be grounded if needed.
M7DJK
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