[KeithsTV]

Using the heated rear window as an aerial dates back to at least the late 70s when you could get a unit that you connected in the power feed to the heating element and it isolated it from the RF point of view and connected it via a matching network to the aerial input of the radio. That really only worked for LW & MW. A different approach was needed for VHF as descibed in a WW article in 1986 (I believe) This required a different form of the heating elements with the feed connections on one side of the car to allow the diplexer to connect to it. The VHF signals were split off and amplified the re-combined with the LW & MW signals before being fed to the radio.

In the article the authors measured the impedances at band 2 frequencies of different cars heated rear windows and the Ford Orion, which was the first car to be fitted with this system, came out as 50ohms. It was I believe an expensive way of fitting an aerial but it did mean no holes had to be made in the wings.

I had a hire car once with this system and whenever the HRW was switched on there was tremendous interference on the radio. I checked and there was a break in one of the elements. I mentioned it when the car was returned and a few weeks later I got the same hire car and the rear screen had been replaced. The radio actually worked when the HRW was on.

Ford fitted it to the Granada, Sierra, Escort and Orion in the mid to late 80s but reverted to roof aerials for their 90s models, presumably due to the cost.

Keith