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Earthing and the radio amateur

Stewart Mason
I've recently joined the IET forums. I replied to a  topic regarding amateur radio and PME on the old forum. Unfortunately I cant access the old forum anymore so I thought it would be best to start a new topic.


So. On the bench there is a transceiver with a metal case. Next to the transceiver there is a antenna tuning unit which is connected to a antenna system which is using an earth rod. Am I right in saying there is a chance of a potential difference between the two metal cases of the equipment regardless if it is a TT, TNS or TNCS?


What would be the ideal solution?  Put the shack on it's own TT supply and bond all the radio equipment back to the MET of the TT and if a earth rod is used for the antennas connect that back to the MET also?


If the TT system was not an option what would be best if the supply was a PME and you didn't want to use balanced antennas removing the use of an earth rod? 


To be honest I've never really given PME's and amateur radio much thought which in hindsight was probably a mistake. I do remember when I did my training an earth rod was recommended for the radios.


Apologies for being so random.


Stewart M0SDM
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  • 0
    John


    A 9:1 unun can be effective when used with a random wire antenna (i.e. one which is not a half wavelength at any frequency you want to work).


    However, the advantage of an end fed half wave antenna is that the feed point impedance is much higher (hence the 49:1 unun) and the VSWR is therefore less susceptible to influence by the proximity of the ground or buildings. This was a factor in my choice as I don't have much height to play with. My wire is indeed a half wavelength at 7MHz but as you can see from the graph it also has good VSWR at 14, 21 and 28MHz. My transceiver is a vintage Yaesu FT-840 which does not have a built in tuner, hence the external LDG. Your built in tuner should have  no trouble with the VSWRs that I'm getting. I haven't tried the antenna at 5MHz but I believe that by adding a 110uH loading coil and an additional 2 metres of wire it should tune up at 80 metres. That's a project for another day.


    The radiation pattern is definitely biased upwards, which explains my good contacts with central and eastern Europe, but also the fact that the nearest QSO I've had was 350 miles away in Scotland. I haven't heard any English amateurs yet!


    The coaxial line choke needs to be good quality. I used this one, and modified it by adding an earth lug to the box which is connected internally to the coax shield on the TX side of the choke:

    https://www.hamgoodies.co.uk/g5rv-choke-balun-400w


    This is the line choke I made for the bonding wire from the rf ground rod to the main earth terminal. The toroids are type 43 from the RSGB shop with 4 turns:

    8dc67703804bbb3c724a169e74255e60-huge-line-filter-1.jpg


    I hope that helps.


    Mike G8GYW
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  • 0
    John


    A 9:1 unun can be effective when used with a random wire antenna (i.e. one which is not a half wavelength at any frequency you want to work).


    However, the advantage of an end fed half wave antenna is that the feed point impedance is much higher (hence the 49:1 unun) and the VSWR is therefore less susceptible to influence by the proximity of the ground or buildings. This was a factor in my choice as I don't have much height to play with. My wire is indeed a half wavelength at 7MHz but as you can see from the graph it also has good VSWR at 14, 21 and 28MHz. My transceiver is a vintage Yaesu FT-840 which does not have a built in tuner, hence the external LDG. Your built in tuner should have  no trouble with the VSWRs that I'm getting. I haven't tried the antenna at 5MHz but I believe that by adding a 110uH loading coil and an additional 2 metres of wire it should tune up at 80 metres. That's a project for another day.


    The radiation pattern is definitely biased upwards, which explains my good contacts with central and eastern Europe, but also the fact that the nearest QSO I've had was 350 miles away in Scotland. I haven't heard any English amateurs yet!


    The coaxial line choke needs to be good quality. I used this one, and modified it by adding an earth lug to the box which is connected internally to the coax shield on the TX side of the choke:

    https://www.hamgoodies.co.uk/g5rv-choke-balun-400w


    This is the line choke I made for the bonding wire from the rf ground rod to the main earth terminal. The toroids are type 43 from the RSGB shop with 4 turns:

    8dc67703804bbb3c724a169e74255e60-huge-line-filter-1.jpg


    I hope that helps.


    Mike G8GYW
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