Power lines as TX aerials.

[colly0410]

Been reading BBC R&D Report 1962-07 on using power lines for TX'ing at VHF: it says that the system has been used successfully on medium waves in Sweden & Japan. Ooer, I've never heard of it, has anyone else?

[Pye Man]

I read something about the Swedish system on the other forum. Regret can't remember the details.

[turretslug]

Looking from the other direction, I've wondered how much 50Hz field strength is around us as a result of the countrywide network of high-amplitude radiator wires?

I thought, using power lines for transmission would entail some slightly fraught isolation problems- but what was once the world's tallest structure was isolated to 120kV at its base, so hardly insurmountable!

[Herald1360]

Is that for "transmitting" , ie radiating, or for signal distribution?

Certainly at HF, power lines do both quite well as anyone trying to listen on HF nowadays will know to their chagrin.

[Niall]

There are a few factors here. Presumably the commercial broadcasting was done with the cooperation of the power company and steps would be taken to limit and control the amount of power line actually used by filtering at the desired end point.

From an ad hoc point of view, a reference point would be those "internet over mains" things which hams and swls hate, which have to have notch filtering in appropriate bands to stop them radiating there. As they are legal, there must be a defined level of RF which is allowed to be coupled into the mains. It would be interesting to know what the maximum is, and how well it would work injecting a modulated RF signal at that level. It would only work if the site was fed from an overhead line, and would be affected by the frequency used depending on what happened at the pole transformer.

[turretslug]

It's easy to see why this might have occurred to people- an aerial system is an expensive piece of infrastructure and occupies (or at least looms over) a lot of land. Seeing power lines marching over otherwise empty countryside certainly gives rise to "take as much as you want, sir" ideas- particularly for MF/LF broadcasting. Separating 100's of RF kW and 100's of mains kV and combining with lightning protection would be a challenge (nowadays, journalists would say, just like a giant ADSL filter....) and possibly the priciest bit- but the components and technology involved wouldn't be much different to those in a typical high-power helix hut anyway. Interesting "might have been" musing and scope for some Frankenstinian megalomania....