ARCHIVE: Australian Ham Radio Discussion Forum ( AHRDF )

Hello to you all,
An article on how I approached an earthing system for my station operating bench, which was based on some rough notes I had put together for my personal web space, was published in AR magazine back in the March-April 2023 edition.  I have tidied up my notes and posted them here in the hope I can get some feedback from others on improvements on my basic concepts.

A sometimes forgotten part of a ham’s shack is the earthing system, I must admit I had only made half hearted attempts at a good station earth in the past.  Which is odd as my previous work life had a large component of making sure all gear was properly earthed.  I am not sure if it was the cost of heavy copper cable and copper bar stock that put me off the scent but I just always seemed to find a reason not to do it.

About 18 months ago I had a light globe moment, why try and use all these fancy earth bars when I had some left-over copper GAS pipe (19mm O/D) in the shed.  A scheme was hatched to use commonly available parts from a hardware store to make a shack earthing system that could be flexible to use and not break the bank.

My operating area is in an L shaped desk so I bought a 19 mm copper elbow to combine with my scrap 19mm pipe, some heavy duty solder and borrowed a small gas torch as my old BIRKO soldering iron was not up to the task, plus a handful of copper saddles to fit the 19mm pipe but not in the traditional way.

Now the method I settled on to attach each bit of the radio gear was to us the copper saddles soldered along each leg of my L shape of pipe as the connection points for flying leads to each piece of radio gear, with the pipe mounted on the back of the desk and earth leads passing through existing holes to the gear.  I firstly measured, cut and soldered my two pieces of 19mm copper tube into the 90 deg bend so I could take it to the shack and mark on it where I needed the connection points to be.  Some areas of the shack had lots of gear grouped close together so multiple copper saddles (attached in the opposite direction to what you would to secure the pipe to the desk) were needed in those spots.

Looking back at it I should have used a pop rivet through each saddle to help locate it on the pipe as soldering of the multiple copper saddles in some areas became tricky when I could not control the heat from the gas flame.  This resulted in a number of oddly angled saddles as they slipped around the pipe when the heat was on.  Note to self, do not do it like that again.
Clean up each saddle and the locations on the pipe where they are to go, then I tinned each of the inside surface of the saddles and then tinned each location on the pipe where the saddles went,  This was a bit messy but effective.  As I mentioned earlier a pop rivet through the U of the saddle and the pipe probably would have been a good way to keep each saddle in the right spot when the heat was applied.

At the end of the copper pipe nearest to my wall (exit point), I flattened the copper pipe using my vice and hammer to create a TAB that I could drill an 8mm hole to attach my cable out to the copper coated earth spike (bought from bunnings) just outside the shack wall.
For the flying lead used between the rear of the radio gear and the earth system, the cable chosen was from the RS components catalogue as it has a high stand count in the cable (84 strands of 0.3mm) to ensure the cable is super flexible with a cross section of 6mm squared , which was one of my main criteria for the cable.  In retrospect this is where I blew my budget as I could have settled on a lower spec cable but once again my previous work experiences drove this choice for flexibility, size and colour.  Our old Quality Assurance person at Jindalee would have been happy with my cable choice for once.

The cable from the end of the copper pipe to the earthing rod was a bit of a fluke, I was given a short length of left over cable from a commercial transmitter’s earth connection install and had hidden it away for a one day project, this proved to be ideal for the purpose BUT on the flip side I could have used multiple runs of the more common household earth cable in a bundle, there is nothing that says it has to be ONE cable.  For the main connecting LUG to the earth rod, I visited my local car parts people and bought a heavy duty crimp lug to fit the cable I had.  If you chose the multi cable bundle then you could use a similar cable lug or many smaller crimp lugs, there is no strict best way here, it is all about getting a low resistance connection.  You must remember this earth is not there to carry high current, just to provide a low impedance path between the radio gear and provide a common earth point for the shack equipment.


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I had a similar idea nearly 10 years ago, copper pipe with lugs added, heavy gauge wire as flyleads.  I agree that it is the RF impedance to earth that becomes a concern, more-so if you are running any unbalanced antennas such as a longwire or a vertical.

I opted for a different approach with a similar overall concept.  I have used 30x30x1.5mm aluminium angle along the back of the shack bench with a Vee cut in one face to allow it to be bent to 90 degrees and thus also allow it to go along just one side of the table top as well as the back. It is screwed into the back edge after all of the interconnection points (for flyleads) have been made and tightened.

A series of 6.5mm countersunk holes plus a swag of 1/4" screws were fed through the angle material and a star washer and 1/4" nut applied on the top side to tighten it up.  My flyleads to the radio gear were simply lengths of RG-213 stripped of the outer sheath after the inner was removed. A Philips #2 screwdriver used to make a hole when flattened, then the last 40-50mm soldered.  That provided a hole that fit over the 1/4" screws, and a wingnut and flat washer was added to the top of each, some screws had multiple flyleads too.  The earthing fly-cables were made as short as possible and the 'far' end was treated similarly, a hole plus flatten plus solder.  I did NOT flatten the coax braid as I wanted the lowest possible inductance.  The 'semi-flexible lead' clamped to yet-another earth rod/spike from Bunnings and fed into the shack and up to the aluminium angle was a piece of LDF4-50 solid (but bendable) coax outer, clamped not soldered.

I think the aluminium angle came from Bunnings, along with the 1.4M earth rod/spike, the LDF4-50 was about 1.2 metres long initially and was cut to size (a junkbox item for me).  The RG-213 was all pre-loved cable and essentially junkbox. I used 1/4" screw hardware simply because I had an excess supply (Bunnings was selling off imperial size screw stuff cheaply at the time ! ). The only soldering involved was the flattened braid where the screw hole was created, easy to do with either a gas or electric iron.

I typically do not have RF feedback or "hot chassis" syndrome, except if I have removed the earthing lead to do something and have forgotten to re-attach it at the back of the radio (etc..).  I have the radios, power supplies, rotator controllers, and even the computer gear all attached via flyleads to the earth bus.  There is still some need to utilise clip-on toroids in some places to minimise RF into audio and computer cabling but that is now a standard process for most operators.

My approach probably cost less than 5PJ's, easier to construct and is probably as effective, the most critical detail being the 'cable' length between the earth rod and the common angle 'earth bus' has to be as short as is absolutely possible.

When I moved to the house here I noted that outside the room I'd selected to be the "shack" the copper mains water pipe came up from the ground and into a hole in the brickwork to feed the house water system.

So from a common point of the radio gear I ran a short heavy gauge cable out through the wall and clamped it to this water pipe.

Heavy AC 50Hz hum on TX audio from just about everything was the result.

So in a garden bed that ran along that wall I drove in a couple of copper earth stakes around a metre apart linked together with heavy gauge cable, connected the shack earth cable to one of the stakes and the AC hum issue disappeared.

My wire HF antenna is off the other end of the house so the shack isn’t close by. My only experience with RF getting in to mike audio was with another wire antenna that ran a tad closer, and that was solved by a tip from Heil Sound re earthing of Kenwood microphones.

See “RFI Removal from Microphone Inputs” here:

https://heilhamradio.com/faqs/

(02-07-2023, 04:08 PM)VK3RX Wrote: [ -> ]When I moved to the house here I noted that outside the room I'd selected to be the "shack" the copper mains water pipe came up from the ground and into a hole in the brickwork to feed the house water system.

So from a common point of the radio gear I ran a short heavy gauge cable out through the wall and clamped it to this water pipe.

Heavy AC 50Hz hum on TX audio from just about everything was the result.

So in a garden bed that ran along that wall I drove in a couple of copper earth stakes around a metre apart linked together with heavy gauge cable, connected the shack earth cable to one of the stakes and the AC hum issue disappeared.

My wire HF antenna is off the other end of the house so the shack isn’t close by. My only experience with RF getting in to mike audio was with another wire antenna that ran a tad closer, and that was solved by a tip from Heil Sound re earthing of Kenwood microphones.

See “RFI Removal from Microphone Inputs” here:

https://heilhamradio.com/faqs/

Hi

Unfortunately there are a few old myths floating around on the issue of earthing.

Some old notes of mine I dug up on earthing. 


It is intended to provide some food for thought on the earthing issue and is not intended to cover all aspects of earthing.

 1          An earth electrode does not behave like a simple resistor.  It is more like complex web of many resistors connected to various different locations.
 2          Earth resistance is measured with an earth resistivity meter (3 or 4 terminals, type dependant).  A normal ohm meter is not suitable for this.
 3          Connecting two electrodes in parallel will not normally halve the earth resistance.  Two earth electrodes spaced their length apart reduces the earth resistance to about 60% of a single one.  Closer electrode spacings result less of a reduction as they begin to act more and more like a single electrode.  The old earthing practice of having an earthing bed of closely spaced electrodes (still found on some sites) was flawed as it does not provide the lower earth resistance envisaged.
 4          Earthing installations normally cater for mains power and lightning requirements and not RF needs. 
 5          Local soil enhancement using water or soil additives will usually produce only minimal reduction in the earth resistance unless implemented over a large area.  They are generally not worth the effort.  If only localised they are in effect a poor substitute for a thicker electrode which does in itself not produce much of an improvement.  The electrode diameter needs to be increased by a factor of around 20 to halve its earth resistance.  However doubling the total length of the electrode is better but does not quite achieve halve the earth resistance.   This all assumes consistent earth resistivity.
 
Mains earthing

The normal earth rod (13mm dia, 1440mm long) at a house premise is for mains earthing purposes.  It relies on all the other earth electrodes in the surrounding area for it to work effectively.  It forms part of the MEN (Multiple Earthed Neutral) system. It caters for 50Hz.  It is not very effective for lightning protection where were the energy is in the form of a short pulse of energy mainly in the 100kHz range associated with a very high voltage and current.  At HF in the MHz range it is even less effective. As the frequency goes up lead length and inductance becomes somewhat important.  The earthing system may possibly even start to behave like the high impedance end of a half wave dipole!

Earth resistance is determined by a number of factors.  The soil resistivity is a major player.  In Perth (Sandgroper Country), the sand behaves more like an insulator than conductor and it is somewhat difficult to achieve a low earth resistance.  The soil resistivity depends on the texture of the soil and this varies with depth and location.  In some instances deep earth electrodes have even finish up partly in the air in voids underground!
 
A Perth site I was involved with in providing lightning protection had experienced repeated lighting strikes.  These resulted in major problems in site operations and high operation costs.  The new earthing system involved installing two loops in the ground one 3 Km long and another one 2 Km long inside it with 7 interconnections.  All using bare 70mm2 copper cable.   Connected to the loops were 59 electrodes (45 x 2.4M long and 15 x 14M long).  Yes, it was a big expensive earthing system!
 
The measured earth resistances were as follows:

 2.4M electrodes
 Ranged from 6 to 980 ohms with the median value 395 ohms, average 406 ohms.

 14M electrodes
 Ranged from 6 to 650 ohms with the median value 180 ohms, average 228 ohms.
 
The few low resistance readings obtained are suspect and probably due to localised area effects.
As can be seen obtaining a low earth resistance in the Perth area is somewhat difficult!
 
So if you expect to get a good, low RF earth resistance using a short spike in the ground you will be sadly disappointed (unless it is in seawater)! 
 
Someone did once say “life was not meant to be easy”.
 
73
 Igor

(03-07-2023, 07:29 PM)VK6ZFG Wrote: [ -> ]The normal earth rod (13mm dia, 1440mm long) at a house premise is for mains earthing purposes.  It relies on all the other earth electrodes in the surrounding area for it to work effectively.  It forms part of the MEN (Multiple Earthed Neutral) system. It caters for 50Hz.  It is not very effective for lightning protection where were the energy is in the form of a short pulse of energy mainly in the 100kHz range associated with a very high voltage and current.  At HF in the MHz range it is even less effective. As the frequency goes up lead length and inductance becomes somewhat important.  The earthing system may possibly even start to behave like the high impedance end of a half wave dipole!

Hi Igor,

I was planning on using a earth stake as well actually - soil type is predominantly clay based in my area, and seems to stay wet most of the year. I hadn't considered that the earthing system might end up as part of the antenna, though thinking about it, of course it could.

What would be a better solution in your experience?

Hi Scott

I would go ahead with the earth stake. It will provide an earthing path. You are fortunate in the soil type you have as it has a lower resistivity and as a result it is easier to obtain a low earth resistance then say in sand.

An alternative to earth rod electrodes is strip electrodes. In simple terms it is an electrode laid horizontally a short distance below ground level. They are not as effective as vertical electrodes as they can only make use of the soil below their level. However they provide an alternative option that can be useful suitable in circumstances where vertical electrode are not very suitable or viable. One can of course use a combination of both. One option is to run a number of strip electrode radials out from an earth stake. If so, the strip electrodes need to go some distance away from the earth electrode so as to get away from the proximity of the vertical electrode. Possible use for old guy wires?

Basically you have to contend with the earth system resistance/impedance and the resistance/impedance of the cable used to get to it. The way RF sees the earthing systems is likely to be different to that seen by lightning as the frequencies involved are somewhat different. Impedance will be of greater importance with RF as the cable length comes into play with regards to wavelength.

From the point of view of lighting protection you have to deal with a short pulse of extremely high current origination from a extremely very high voltage source. The high voltage means it can jump over locations that present obstacles to it. The high voltage and very high current involved means that you are dealing with a short pulse of very high energy. This requires heavy cabling and strong fixing for the cabling to cope with the heat and forces involved in the event of a direct lightning strike.

Peter's article deals with achieving the connection to the actual earthing point from the RF point of view.

The important thing is to have all the electronic equipment earthed together so that the potential difference between it is kept as low as possible. During a lighting strike any difference between the equipment will translate into a voltage difference and if high can have an detrimental impact on the equipment. Now if the equipment location is some distance from the earthing electrode system the equipment will go up in voltage with reference to the local earth. If this is low it is not a problem but can be if it is referenced to a remote earth as the local earth voltage will rise above the "real" earth point due to its earth resistance as the remote earth will be at the "real" earth potential.

73

Igor