THE TRANSMISSION GALLERY
|Photos by Martin Brown||Page last updated: 2017-10-10|
|On the 18th November 2014, the old UHF stack was removed by helicopter lift, and replaced with a new disaster recovery (for Crystal Palace), UHF aerial. Once operational, this new aerial will permit Croydon to transmit the 6 main DTT multiplexes, with an ERP only 3 dB's lower than Crystal Palace.|
There is a link to a YouTube video from "The Bridge Networks North", who managed the project, at the foot of this page, with pictures of the helicopter lift.
|The new UHF DR aerial.|
|The 2 square boxes above the new UHF aerial stack are understood to be dampers, to reduce oscillations of the structure.|
Dave Thickett kindly supplied the following on this arrangement:
I can only speculate as this antenna was provided by a competitor but . . . . in other places, we have designed liquid tuned dampers to fit on top of an antenna that could oscillate due to the combined dynamic effect of a long cantilever on top of a mast or tower that itself oscillates.
The mast and antenna combined will have a resonant frequency of a few Hz plus various harmonics and the width and depth of the water tanks, plus the 'baffles' inside are set to provide a 'sloshing frequency' that absorbs energy from the tower oscillation, reducing it's amplitude. I'm sure we have provided some of the 16 Lambda cardioid antennas with built in liquid dampers. I think the concept of vortex induced vibration is well documented on the web and water tanks are one way to reduce these effects.
|The old Channel 5 aerial. Top part of the old stack.|
|The old analogue DR aerial. Lower part of the old stack.|
|Six tiers of crossed shrouded UHF logs for the London local TV mux. The aerials face south and east and operates as a single frequency network with the local TV transmissions from Crystal Palace.|
The Bridge Networks North YouTube video
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