I am considering putting my ham rig my bedroom.  The property is PME fed.  I thought I would use an mains isolation transformer 240v - 240v  1.5Kw and isolate the earth at output sockets.  There is a radiator in the bedroom which is fairly close to where the station will be.


The antenna has an earth rod installed well outside the PME field of anywhere.  The station has an earth bar to which all metalwork of the station is connected.


This is like a fully isolated TT supply with no connection  to the MET and fully isolated (by TX) line connections.


Your comments would be appreciated.


Mike. GW6UWW

If your central heating has metal pipework, and there is no bonding in the property between the station earth bar and the PME system, you can expect a touch voltage between the earthing system of the station and the radiator. This voltage can be anything from a few Volts, to perhaps 10s of Volts, and is a result of diverted neutral currents in the PME supply. Certainly on occasion, the voltage could be enough to be felt, and potentially enough to cause a serious electric shock for children or persons with some medical conditions, especially if they are hot and sweaty and there is a large contact area.



If there is an electrical fault in your installation, or a broken Neutral of the PME supply, the voltage can become hazardous - in the latter instance, perhaps for some considerable time.


The same is true of any metalwork connected to the protective earthing in the main house installation - such as metal plate switches, etc., and fixing screws of accessories - and of course anything connected to the protective earth of the primary side of your isolating transformer.


In practice, two things could be done about the radiator:

• Wooden radiator cover, and remove the antenna connection when you need to clean or work on the radiator.

• Fit plastic sections of pipework in the feed and return from the radiator

Everything else - cover up with insulation or replace with a non-conducting equivalent product - or move out of reach

Thanks for the reply Andy.  After I had posted, it had suddenly dawned on me that the two earth systems would still be within reach of each other!  My thought was that with the radio supply mains being fed through an isolation TX it would be a safer option.  Also, it means that the aerial system, which is connected to the radio, has its own earth stake and I did not want to have any link to the noisy PME earth.  An rf filter in the mains feed to the radio would rf isolate from the house wiring.  The radiator is 4 feet from the radio.  The radiator, which is on the central heating boiler system, could be boxed in?  To make things a little clearer,  Isolation TX fed from house ring.  Ring main earth removed from TX outlet socket.  Line fed from TX via rf filter to radio.  Metal work at station earthed to aerial system?

Mike.

I think our posts have got out of step, sorry about that.  Yes, it is a thought about insulating the feeds to the radiator and or boxing it in.  The earth system from the antenna does have a means of disconnection and lightening protection so no problem there.  It has always been a worry of mine about lost neutrals which is one of the reasons I am not keen on PME.  On the other hand, if TT systems are not maintained??!!  Thanks for the replies.

Kind regards,

Mike.

I also have worries about getting RF into the mains via bonding. If you don't mind the isolation transformer, this will give you the best of all worlds and you can freely connect the equipment to the RF Earth rod. The secondary of the isolating transformer will need to be made into a TN-S supply by earthing one end of the secondary to the RF earth (Earth neutral bond), and you may wish to fit an RCD to the secondary for additional safety. If the transformer has a screen connection this should connect to the RF Earth helping to prevent RF from getting into the mains supply. However you still have some degree of two Earthing systems in the shack, and bonding them together via an RF choke (wound with largeish wire and suitable ferrites) might be a good solution, or perhaps preventing contact with radiators etc with insulating cases.. Obviously the transformer must feed all the sockets in the room, again to prevent access to both Earthing systems at once. Even a 100W rig can cause TVI or network disruption over quite an area if the SWR is not good inside the shack, so the connections to the ATU and Earth rod need to be as short as possible.


On another note, you really need to get your wire higher if possible, as the radiation angle will be very high if it is low. Verticals can be very good in this situation and can be hidden quite well, or even fitted to the Chimney with radials on the roof as the ground plane, and both can be loaded with inductors to get virtual extra length.


73, G8FNR

Hi David,  I shall be boxing in the radiator to remove the touch problem.  I agree with you over the Earth-Neutral bond and it was already on the list.  As far as the TVI goes, I like to try and run on minimal Watts, also, antennas are external to the building.  The bedroom is quite large and the position of the rig is in a remote corner at least 12 foot from any other earth.  Double insulated bedside lamp and battery powered hoover.  Both of us are OLDIES now so no kids!

73, Mike GW6UWW

Ha that GW6 reminds me of the old television transmission licences, G6ANT/T for example. Time passes.....

Oh and JP. Vertical aerials are pretty good, particularly if you make it perhaps 60 feet or so, and have a good Earth system. They also don't show much if the top 20 or 30 feet is a thin fibreglass thing, which used to be on sale as a car accessory. It doesn't matter if it blows in the wind, still works fine. A friend of mine who sadly passed away, G3SXY, used to have similar and it was excellent on all bands, particularly around Europe on 80m. A long long wire is good too, but few have the space. G3LYW used to have a couple of hundred metres, high up, and a few (8) PL509s in parallel on top band, it was called the "dog feeding unit" when in use for some reason, lost in the mists of time! So that's 8A at 500V into the PA. Hmm......Very loud though.

One ship that I was on, GXIC, had a 10 metre vertical whip mounted on the ships monkey island which was about 110 feet above the water line. The base of the whip fed into the auto- ATU for the Skanti TRP-8750 good for 600-750 watts. 1.6 - 30 MHz. The only problem was that on radio-telex the international spec for radio-telex did not require equipment to be able to tolerate the propagation delay if you were the other side of the world, which we often were - New Zealand.  But saying that, I could work BT's Portishead Radio on 12 MHz Radio Telex using that whip with the power set to about 10 watts. Similarly on full power I could trigger Niton Radio's Radio Telex system on around 3 MHz, but never managed a two-way communication; again that was using the same whip and ATU.

Clive