BT microwave network history
 

This is an excellent historical description of the BT network. Going by the bits I had some involvement in, it's spot-on.
http://dgsys.co.uk/btmicrowave/

John

Re: BT microwave network history
 

That’s interesting John thanks for sharing. I never worked for BT but I did work for Mercury and I maintained radio links across the north east and Cumbria. We had Siemens 140Mbps and NEC 34MBps for long/medium haul trunk network and also used 2Mbps extensively for customer connections, using DMC, Ferranti and others.
Believe it or not there were still Siemens radios operational until a few years ago and I know of NECs that we’re never switched of for over 20 years and had no faults.
Mostly replaced by fibre now but microwave is still used where access is a problem or resilience is required, the radios are now 10Mbps.

There’s not much on Mercury radio but it does get a mention here:
http://www.cumbria-industries.org.uk...ommunications/
It’s not just BT who relied on microwave radio connections to and via Cumbria. In 1981 Mercury Communications was formed as a subsidiary of Cable and Wireless to challenge BT in the provision of national telecommunications services. Mercury communications established a national network based on Siemens 140Mbps (Mega Bits Per Second) microwave radio equipment. The system required several relays in Cumbria, these were known as Scout Hill radio site and Grey Rigg radio site. These two locations enabled connectivity from Manchester to Scotland and also provided services for customers in the area.


John

Re: BT microwave network history
 

Too late to amend, I just wanted to add this ...

Re: BT microwave network history
 

Not sure if it is still in the gallery but M.O.S.I. Manchester had one of the 10ft dishes and a STC sender/receiver complete in its cabinet from the Manchester Kirk o’Shotts microwave link.

Re: BT microwave network history
 

Another ex-Mercury engineer here, transferred from C&W after an overseas contract. I was customer links though, rather than trunks. As you say, where possible fibre has replaced microwave now. Expensive to install, but cheaper to run and upgrade.

Re: BT microwave network history
 

Fibre can fail if a sloppy excavator driver gets let loose in the wrong place.

Re: BT microwave network history
 

And line of sight can be lost, although important traffic is normally protected. The point is we (they) have a choice nowadays and route planning is eased.

Re: BT microwave network history
 

Line of sight was most certainly lost on occasion by "Snow in the dish". Ordinary snow would have little effect other than a modest fade at 6GHz, but a certain variety of wet, sticky snow could build up a wedge shaped snowdrift on the face of the dish which would cause the beam to develop a squint and to lose alignment. I've watched the AGC levels gradually fall until the link became unusable. There were protection channels, but they were multiplexed into the same system, and would fail as well. (cue lots of red lights and alarm bells !)
The snow would eventually slip down and off the dish, and the AGC levels on all receivers sharing the aerial would abruptly jump back to normal.

I understand this was one of the reasons why many of the open-faced dishes were later replaced by covered face "Low sidelobe" ones.

John

Re: BT microwave network history
 

Spent a few years on investigating local and core microwave radio link failures myself and indeed line of site can be compromised. A few instances spring to mind: trees, and rain, snow and ice obviously, but then gasometers, wheelbarrows on scaffolding planks, ships on the Manchester Ship canal, new buildings - and not all links with diversity, happy days!

Re: BT microwave network history
 

Is that a picture of Eston Nab? That mast seems very familiar. I visited and worked on a lot of the radio sites in the Northumberland/Durham/Cumbria/Cleveland area in the eighties and nineties, on microwave linked private wide area networks, although never for BT. I occasionally used to cross paths with the Mercury engineers, at places like Grayrigg. Great job if the weather was nice.
Alan.

Re: BT microwave network history
 

Known as "Backhoe fading" in some circles....!

Re: BT microwave network history
 

Yes it is, well spotted!

John

Re: BT microwave network history
 

Yes - which is why the 'dishes' at exposed sites generally had an extension with a diaphragm across the front to exclude the weather, along with a heater to reduce icing.

One link I was involved with in Scotland [onward-linking to oil-rigs via Aberdeen] was fully-equipped with de-icing heaters, but when these were called-on to work in anger because of freezing rain, it failed a few minutes after the heaters were activated. Turned out that whoever had installed it had hooked the heaters up to the regulated/current-limited 48VDC supply intended for the communications-electronics rather than the rather less-controlled generic 48V supply.

Re: BT microwave network history
 

Known as callout and £££ in mine!

Re: BT microwave network history
 

We used to get dishes damaged with naughty people using them as target practice for air rifles (and probably live ammunition seeing some of the holes! The weather skins used to rip also, or maybe the same hooligans used to like the noise of the pellets bouncing off them. The ecapsulated yagis used to drop the shroud off and leave a tiny stub of an aerial which in some cases left the link up, albeit a tad noisy. Many a call out to links dropping out because the rain or mist was of a particular "type" or cancellation due to ground conductivity causing reflections. And as has been said already, those big yellow cable finders. If there's a buried cable, they will find it!
Alan.

Re: BT microwave network history
 

There was a big collection of dishes on Holyhead mountain until a few years ago - BT I believe. These have all now been removed. I was wondering if anyone knew what the new routes/methods replaced them?

Re: BT microwave network history
 

A few years ago I happened to be outside what I think is Lark Stoke transmitter site. A public footpath passes just outside the fence. Just inside the fence was a satellite dish, maybe 5ft across, which some helpful people had partly covered with clods of earth. I guess that will not assist with bit error rates?

Re: BT microwave network history
 

Not strictly a link fault callout. HP went into the modem market with some rather expensive thoroughly engineered (the boards were bought in!) modems. Various PTTs bought them to link to remote test equipment in remote places.

One modem sold to one rather large PTT (they thought they were the only one on the planet) couldn't train and come up at all. So an Engineer (Capital letter 'E', BSc and two MScs) - one of the designers, was sent out to investigate.... From Scotland to Hawaii. It turned out the guy at the Hawaii end hadn't checked what settings the manual said to use for the system config at his end, and had phoned the guy at the US mainland end and asked him how his switches were set. Oddly, it didn't work, so he called it in as a fault and it was escalated. With new type equipment, it quickly escalated very high indeed. This served to get someone out there very quickly, but it also made sure the goof was known in all the highest strata of the Bell empire. Wonder if they refunded HP the cost?

The chap involved did say he'd enjoyed the trip.

David

Re: BT microwave network history
 

RW- something to tickle your fancy. I've heard of one single channel radio link from some Scottish island to mainland, where twice a day the link failed . It transpired that a planner had failed to allow for the sea level at high tide, which prevented a line of sight between masts. Another one. At one time I was maintenance officer for a Highland Micro wave radio link from Mull to a remote peninsula. We had a recorder on one of the group 84deltas and from that I could tell the state of sea and weather outside.On a flat calm, with no wind, the trace was flat. With a sea ,the trace reflected the state of the sea.

Re: BT microwave network history
 

See also post 9. We did have a gasholder anomaly (nothing to do with me, honest) and also a link that gradually deteriorated as a pit spoil heap got higher.