TV Breakdown Appreciation Thread

Also I don't think the BT Tower has any facilities for 'ad hoc' microwave links. It's never been their stock in trade, that's always been a broadcaster thing. However, and commseng will know, I don't think sub 10 GHz SHF terrestrial links are particularly susceptible to rain fade?

It certainly does - the 35th floor (above the observation decks but below the 'infoband') is open to the elements just for this purpose. It's also handy for taking photos of the view without reflections.

That's interesting. The "Turret Room" at Emley was originally conceived for the same purpose, with specially formulated glass that wouldn't attenuate the signal too much. I daresay that doesn't get too much use these days.

Yes, the distances are considerably shorter by thousands of miles, and you are not going through an awful lot of water in the same way.
The link budget for a microwave link has far higher fade margins than a satellite one, where if you get more than 8dB you are doing very well indeed.

I think one of the issues at the Hammy Odeon is the parking. The two trucks that were there were parked down the obvious road with a limited view of the sky, and therefore the choice of satellites for main and backup was reduced.
The third truck may have been parked further away, possibly fed via fibre and having to run on its own genny (with the risk that could fail) and with a far bigger choice of satellites well away from the narrow choice for the main and backup.
A storm going over West London may wipe out those links at different times. It would be messy, and require switching between feeds, but better than it falling off air completely.

UKI-1 is a 3m dish. I last used it as a transmit dish as the BBC backup at the London Olympics - the idea being should the entire IBC fail, we could still get something out. It wasn't used in anger.
Having a big dish does increase the gain and helps the link budget.
For the transmit end you don't have to run the HPAs as hard, and you have gain up your sleeve.
If a storm comes over, you can ride the gain of the amplifiers a little - but you shouldn't do it looking at yourself back, as you are seeing yourself through the storm twice.
The receive side you cannot do that, so having the bigger dish doesn't give quite the same flexibility.
It is horrible to be on site and watch your signal just suddenly disappear, as there is only so far you can ride out the storm.
I am aware that even the big ground stations have been wiped out with storms, so if a 6m or even 18m dish can lose a signal, the difference between those you can mount on a truck (between 1.2m and 2.4m) is not going to be a major factor.

At Sky's uplink site at Chilworth they constantly watch the met office radar scans for trouble. They have a back up site not too far away, but far enough away that it shouldn't be affected at the same time by the same storm !

We have done ad hoc links into the Tower, but not often. Sometimes it has been for BT themselves.
I doubt the view from Hammersmith to the Tower would have been line of sight, and may have needed a midpoint, which is not easy to negociate and rig at very short notice.
Bear in mind that last minute requests are all about exploring options - and working out what the potential costs associated with each of them is.
In the old days it would have been a link direct into Crystal Palace, but all that masthead receive infrastructure was torn out years ago.

Is there still a microwave link from the roof of the Albert Hall to the roof of BH, (or has there ever been one ?)

It's worth their while, as the whole business relies on keeping the service to home going.
Believe me, I always keep an eye on the weather forecast when doing uplinks or downlinks.
It's not just the rain, high winds can play havoc with the dish, especially the larger ones.
It's all very well having a lot of gain, but the beamwidth is much narrower - so a gust of wind is more likely to take you off air.
I've braced dishes with scaffold tubes at times!

Yes a 5GHz link which carried the digital feed for Radio 3 direct to the roof of LBH was used for a few years, but now it will be IP based.
You can see a couple of the helix antennas on the photo below.
https://www.flickr.com/photos/115059469@N03/12858398133/

Ha, yes, I was at an OB in South Africa a few years ago, the uplink vehicle arrived, and it was a flatbed Toyota pickup, with duff stabilising jacks. What fun !

It's quite spooky to stand under the dishes at Chilworth, their beam-width is obviously so narrow they have servos that constantly nudge the beam back towards the satellite as it drifts around in space (within its 200 (?) mile 'box')

At the other end of the deal, last weekend I put up a 45cm 'Sky' minidish, 19.2, 23.5 and 28.2 all merge into each other as you pan it. I thought I had 28.2, until I fired up the receiver and it filled up with German stuff instead !