Ok, Tried again tonight. This time was getting the signal on Channel 20 instead of 19.
I was using a battery backup supply to power the set, and even though the power socket was switched off, the Mains Earth was still coupled through the powersupply to the ground output on the 12v side.
Unplugging the plug from the wall socket caused the signal to disappear. If I held the power plug near another cable that was plugged in, then I get the signal again (with more attenuation).
So it is not coming through the antenna, but through the mains wiring.
The Utility (Eskom) has been changing all the Kwh meters to smart metering in the surrounding area. These meters communicate back to a Concentator at the Eskom Transformer, and they will also be communicating with a consumer display unit that plugs in in the customers house. The Meter is also wired to a relay transmitter, that will be communicating to a relay in the customer's D.B. in order to switch off Pool Pumps, Geysers, etc if the overall demand is too high. All this intercommunication is done through Power Line Communication.
I guess I am picking up some signalling from other clients on the same transformer.
Will be fun in the future, if there is no encryption, to decode the communications, and then inject my own signalling on the powerline, and play havoc with the Load Control Relays, and the Consumer display units (which I understand can display text, flashing lights,etc), that could entertain me for hours (and probably land me in a bucket load of trouble)
On a side note, the concentrator communicates back to the utility using a GSM modem.
Peter