Aerial photography - Ancient Gallery

This installation was located in an area where ‘ghosting’, or multipath reception, was a problem. The large array with three long elements was for Band I channel 2, vertical polarisation. The middle element was driven, with a reflector to the rear, these two together forming the familiar ‘H’ aerial. The addition of a director improved the forward gain and thus the directivity. Some three element band I aerials had a folded dipole for better cable matching.

Near the top of the mast was a Group ‘A’ UHF array, horizontally polarised. This was an example of the 1960s Antiference design that had a balun hanging under the dipole, with the cable swinging in the breeze. Note that the UHF array was directed in roughly the opposite direction to the VHF arrays. This would be because the ghosting at UHF from the local transmitter was intolerable, forcing the use of a more remote UHF station. This was quite a common situation. One of the first things we learnt when UHF came along was that in a given location, the ghosting at UHF would always be much, much, worse than at VHF. The UHF array is really much too close to the VHF elements, but that sort of compromise was common in those days.

The Band III aerial (for channel 10, vertical) was unusual, because stacked pairs normally had 8 or 11 elements on each side. In this case there were five. Note the parallel wires used to form a transmission line. The feeder cable was connected centrally across them. Stacked arrays were often used to combat ghosting. Because of the large physical size of VHF aerials it wasn’t possible to improve directivity by adding large numbers of elements, so exploiting the phase cancellation properties of a stacked pair was a much-used technique.

It’s interesting that the neighbour manages with a much more modest installation. The ‘dipole and five’ was just about the least ‘ghost-resistant’ array ever made!

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