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THE TRANSMISSION GALLERY

HUGHENDEN

Photos by Martin Brown Page last updated: 2017-03-15

New transmit aerials - March 2017

In preparation for 700 MHz clearance in 2018, the transmit aerials at Hughenden were replaced on 14th March 2017. The UHF channel assignments here are expected to be changed from the current lower band V allocation. Although UHF log periodics aerials are wideband, the precise alignment of a 4 tier array of crossed logs is frequency dependent, as mb21 contributor TCPD explains:

The log periodic antennas themselves are wideband, however there are other things to consider in the design of the complete array. Vertical spacing of the tiers is different for Band 4, lower and upper Band 5 which affects the gain and VRP. The crossover point in crossed log array is near the front for high channels and near the back for low channels: affects the HRP. Some of the components used in the distribution system (2,3,4 and 6way splitters) are not wideband. Arrays where the logs are crossed at more than 120 degrees are particularly critical. Because the antennas are almost firing at each other, the coupling between them is greater. Move down in frequency on a band 5 array and they really are firing at each other because the active part moves from the front to the back, and also the tiers are too close together. So while in some cases the changes in performance from a frequency change might be acceptable, in other cases they just won't work at all.




Eight new log periodics and steelwork, gleaming in the March sunshine.


Left: Roger Pipers Picture from Nov 2007. Right: My Picture from March 2017.



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