On 27/07/2023 16:12, J. P. Gilliver wrote:
> But should something break, the
> chambers inside the mountain would fill with water_very_ fast, hence
> the need for a swift escape.

We were told that someone had worked out how quickly it would fill with
water is a pipe failed (they are *BIG* pipes!).

There would be no hope of escape, it would fill much too fast.

On Thu 27/07/2023 19:40, MB wrote:
> On 27/07/2023 16:12, J. P. Gilliver wrote:
>> But should something break, the
>> chambers inside the mountain would fill with water_very_  fast, hence
>> the need for a swift escape.
>
>
>
> We were told that someone had worked out how quickly it would fill with
> water is a pipe failed (they are *BIG* pipes!).
>
> There would be no hope of escape, it would fill much too fast.
>
>
>

In theory if all six units were spinning on air (as they would be just
before the adverts in the latest James Bond film being shown on TV and a
cuppa would be needed) they could go from 0 to 1320MW in 10.4 seconds.
Conversely a demand stop would take them from 1320MW to zero in a little
over 4 seconds BUT the catch pond (about the size of the old Wembley
Stadium) at the top of the main 525ft drop shaft would fill in less than
10 seconds from a shaft of water 30m across and theoretically over 50m
high - but I don't think they ever tried it. The pipes feeding the units
were 2m diameter with a valve like a perforated golf ball. At full gen
the water would run through those valves at something over 1000psi and
85000 gallons a second.

The best bit? It was designed to run on demand for typically about 15-30
minutes (maximum to drain Marchlyn Mawr - the header tank if you like -
was reckoned to be about 90 mins) whilst gas turbines (around 4 minutes)
or nuclear (about 10 minutes) came on line. The place was costed to
build as (IMSMC) about £40m - it actually cost £484m! However when they
started using it they found it was so efficient they could let it run
for most of the load shedding period. Doing so it cost something like 20
months to pay for itself!!!

If you have a look at Google sky view and follow the entry road you will
see the south facing entrance tunnel (green spot on it). Then zoom out
scan away NE to find Marchlyn Mawr. If you take a diagonal line SW from
MM and zoom in a bit you will eventually see the surge pond - long oval
with the circular surge shaft in the centre - and if you zoom in a bit
more following the same line you will see another circular object which
has a grille on the top. If the station flooded there was a vertical
ladder underneath this last object, the top of which was about 30ft
below the grille but the platform atop the ladder would have been about
6ft above the highest water level!

They generate at 11KV and about 18500A but there is a 275KV sub-station
inside the mountain which takes the power away in water-cooled pipes
about 9 miles before going overhead. The whole place can be controlled
locally by three shift staff, or remotely from Connah's Quay on Deeside.

It is now known as 'Electric Mountain.' A TV (slightly
anti-nuclear/Thatcher) drama called Edge of Darkness starring Bob Peck
had large sections (allegedly Aldermaston) filmed inside Dinorwic in
1985. It was repeated (for the first time?) earlier this year.

On 23/07/2023 11:29, Brian Gaff wrote:
192MHz was a Russian space comms frequency.
I remember a long time ago hearing very occasional weak Russian sounding
stuff on 143.625MHz.

> Yes well nowadays you would not get away with this, but some of the Russian
> space communication some years ago was in the middle of band 3. You could
> when in range, clearly hear them talking and joking in mostly Russian but
> some English.
> Brian
>

--
Brian Gregory (in England).

On 25/07/2023 16:14, Liz Tuddenham wrote:
> There used to be studio talkback on narrow-band FM from the Mendip
> transmitter mast, presumably for the benefit of roving OB units. It was
> entertaining listening to the rehearsals for the evening local
> television news - especially when a lady announcer's mic became
> unclipped and it had to be retrieved.
>
> I seem to remember the transmission was around 175 Mc/s, but I may be
> mistaken.

When on the South coast or Isle of Wight we could sometimes hear the
same kind of thing for BBC South on, if I remember correctly exactly 141MHz.

--
Brian Gregory (in England).

In message <u9umgo$1vmho$1@dont-email.me> at Thu, 27 Jul 2023 22:10:47,
Woody <harrogate3@ntlworld.com> writes
>On Thu 27/07/2023 19:40, MB wrote:
>> On 27/07/2023 16:12, J. P. Gilliver wrote:
>>> But should something break, the
>>> chambers inside the mountain would fill with water_very_  fast, hence
>>> the need for a swift escape.
>> We were told that someone had worked out how quickly it would fill
>>with water is a pipe failed (they are *BIG* pipes!).
>> There would be no hope of escape, it would fill much too fast.
>>
>
>In theory if all six units were spinning on air (as they would be just
>before the adverts in the latest James Bond film being shown on TV and
>a cuppa would be needed) they could go from 0 to 1320MW in 10.4
>seconds. Conversely a demand stop would take them from 1320MW to zero
>in a little over 4 seconds BUT the catch pond (about the size of the
>old Wembley Stadium) at the top of the main 525ft drop shaft would fill
>in less than 10 seconds from a shaft of water 30m across and
>theoretically over 50m high - but I don't think they ever tried it. The
[]
>They generate at 11KV and about 18500A but there is a 275KV sub-station
>inside the mountain which takes the power away in water-cooled pipes
>about 9 miles before going overhead. The whole place can be controlled
>locally by three shift staff, or remotely from Connah's Quay on Deeside.

It kept - or at least helped - the company I worked for briefly (about
1979-'82 I think), Reyrolle Switchgear, in business for some years.
>
>It is now known as 'Electric Mountain.' A TV (slightly
>anti-nuclear/Thatcher) drama called Edge of Darkness starring Bob Peck
>had large sections (allegedly Aldermaston) filmed inside Dinorwic in
>1985. It was repeated (for the first time?) earlier this year.

Is it open to the public? Sounds like it'd be quite interesting to visit
(for those of us of an engineering bent).
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

"If even one person" arguments allow the perfect to become the enemy of the
good, and thus they tend to cause more harm than good.
- Jimmy Akins quoted by Scott Adams, 2015-5-5

On 28/07/2023 03:59, J. P. Gilliver wrote:
> Is it open to the public? Sounds like it'd be quite interesting to visit
> (for those of us of an engineering bent).

Cruachan has a visitor centre with exhibition and cafe - with Pine
Martens regularly seen outside eating scraps.

You can then be taken to a viewing gallery at the end of the tunnel
where you can see the generators. We got to into the generator hall and
control room - fortunately none were running so it was quiet!

You used to be able to borrow the gate key to drive up to the dam but
too many people did not return the kay so they stopped that. We had a
key for access to a site up there so got to drive over the dam.

On 28/07/2023 02:42, Brian Gregory wrote:
> When on the South coast or Isle of Wight we could sometimes hear the
> same kind of thing for BBC South on, if I remember correctly exactly 141MHz.

Transmitter Group had a channel on 141 and think possibly other people,
mainly OBs.

I have a photograph that I took during the Investiture of Charlie, OBs
had a big group of RTs including a channel that was kept in reserve so
the nationalists would not know it and so be able to monitor / jam.

In article <u9vn6f$269r0$1@dont-email.me>,
MB <MB@nospam.net> wrote:
> On 28/07/2023 03:59, J. P. Gilliver wrote:
> > Is it open to the public? Sounds like it'd be quite interesting to visit
> > (for those of us of an engineering bent).

> Cruachan has a visitor centre with exhibition and cafe - with Pine
> Martens regularly seen outside eating scraps.

> You can then be taken to a viewing gallery at the end of the tunnel
> where you can see the generators. We got to into the generator hall and
> control room - fortunately none were running so it was quiet!

> You used to be able to borrow the gate key to drive up to the dam but
> too many people did not return the kay so they stopped that. We had a
> key for access to a site up there so got to drive over the dam.

Just after the Torosay transmitter came on air I was in the area
carryingout a survey and I stopped at Cruachan, which was new. I got a
look round - free.

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On 28/07/2023 09:15, charles wrote:
> Just after the Torosay transmitter came on air I was in the area
> carryingout a survey and I stopped at Cruachan, which was new. I got a
> look round - free.

It can be a handy place for a coffee in the cafe because not much along
there.

In article <ua0277$279jm$2@dont-email.me>,
MB <MB@nospam.net> wrote:
> On 28/07/2023 09:15, charles wrote:
> > Just after the Torosay transmitter came on air I was in the area
> > carryingout a survey and I stopped at Cruachan, which was new. I got a
> > look round - free.

> It can be a handy place for a coffee in the cafe because not much along
> there.

Indeed so. I was only a few miles away (Dalmally) last month

--
from KT24 in Surrey, England - sent from my RISC OS 4té
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On Tue, 25 Jul 2023 16:14:55 +0100, Liz Tuddenham
<liz@poppyrecords.invalid.invalid> wrote:

> There used to be studio talkback on narrow-band FM from the Mendip
> transmitter mast, presumably for the benefit of roving OB units.

Yes, that was ours.

> It was entertaining listening to the rehearsals for the evening local
> television news - especially when a lady announcer's mic became
> unclipped and it had to be retrieved.

Was it?

> I seem to remember the transmission was around 175 Mc/s, but I may be
> mistaken.

Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
exact frequency of Ch 2 which was used from other locations, but it was
in the same ball-park.

Paul Ratcliffe <abuse@orac12.clara34.co56.uk78> wrote:

> On Tue, 25 Jul 2023 16:14:55 +0100, Liz Tuddenham
> <liz@poppyrecords.invalid.invalid> wrote:
>
> > There used to be studio talkback on narrow-band FM from the Mendip
> > transmitter mast, presumably for the benefit of roving OB units.
>
> Yes, that was ours.

You had an unofficial fan club.

> > It was entertaining listening to the rehearsals for the evening local
> > television news - especially when a lady announcer's mic became
> > unclipped and it had to be retrieved.
>
> Was it?

She retrived it herself despite the gallant offers of help from a
co-presenter.

> > I seem to remember the transmission was around 175 Mc/s, but I may be
> > mistaken.
>
> Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
> exact frequency of Ch 2 which was used from other locations, but it was
> in the same ball-park.

Thanks, I wasn't sure about that.

--
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Sorry. Just noticed I messed up the quoting on that.

--
Brian Gregory (in England).

On 29/07/2023 01:08, Paul Ratcliffe wrote:
> Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the exact
> frequency of Ch 2 which was used from other locations, but it was in the
> same ball-park.

Could it have been that the mobile channels were around 141 MHz and 170
MHz was used for linking back to the base?

On Sat 29/07/2023 16:13, MB wrote:
> On 29/07/2023 01:08, Paul Ratcliffe wrote:
>> Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
>> exact frequency of Ch 2 which was used from other locations, but it
>> was in the same ball-park.
>
>
>
> Could it have been that the mobile channels were around 141 MHz and 170
> MHz was used for linking back to the base?
>
>
>
>

IMSMC the long range radio mics as used at, for example, the Grand
National, were around 140-141MHz as noted. Some frequencies in Band IV
and later Band V were also used. Studio radio mics were mostly about
174MHz but when Band IV became available for mobile radio and data they
were shifted onto TV channel 69 (about 860MHz) where they remain to this
day (I think). Interesting that the UK UHF band was 21-69 but whilst 21
was used (used even more now with DTTV) 69 was never allocated.

On 29/07/2023 16:52, Woody wrote:
> On Sat 29/07/2023 16:13, MB wrote:
>> On 29/07/2023 01:08, Paul Ratcliffe wrote:
>>> Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
>>> exact frequency of Ch 2 which was used from other locations, but it
>>> was in the same ball-park.
>>
>>
>>
>> Could it have been that the mobile channels were around 141 MHz and
>> 170 MHz was used for linking back to the base?
>>
>>
>>
>>
>
> IMSMC the long range radio mics as used at, for example, the Grand
> National, were around 140-141MHz as noted. Some frequencies in Band IV
> and later Band V were also used. Studio radio mics were mostly about
> 174MHz but when Band IV became available for mobile radio and data
> they were shifted onto TV channel 69 (about 860MHz) where they remain
> to this day (I think). Interesting that the UK UHF band was 21-69 but
> whilst 21 was used (used even more now with DTTV) 69 was never allocated.

The 141 MHz Rx/Tx at Mendip under discussion was radio talkback, (to
allow off air comms between the studio, and the director and presenters
on site at the OB, nothing to do with radio mics. A presenter will often
wear two devices, radio talkback (normally for them rx only to hear the
director etc) and radio mic, tx only (for their voice to be heard on
air, and obviously inside the truck, and back at the studio) All that
said, the body worn talkback kit will be low power, and only Rx'ing from
the OB Truck. The radio talkback to and from the studio (via Mendip in
this case) was/still is a different higher power device, using dipoles
or a yagi on the roof of the truck.

On 31/07/2023 09:48, Mark Carver wrote:
> The 141 MHz Rx/Tx at Mendip under discussion was radio talkback, (to
> allow off air comms between the studio, and the director and presenters
> on site at the OB, nothing to do with radio mics. A presenter will often
> wear two devices, radio talkback (normally for them rx only to hear the
> director etc) and radio mic, tx only (for their voice to be heard on
> air, and obviously inside the truck, and back at the studio) All that
> said, the body worn talkback kit will be low power, and only Rx'ing from
> the OB Truck. The radio talkback to and from the studio (via Mendip in
> this case) was/still is a different higher power device, using dipoles
> or a yagi on the roof of the truck.

Just seemed a possibility, we had a 141 MHz base station liked to a 47
MHz base station with talkthrough. Worked very well with good range at
least when there were no East European fishing boats coming through on
Sporadic E :-)

On Sat, 29 Jul 2023 14:39:02 +0100, Liz Tuddenham
<liz@poppyrecords.invalid.invalid> wrote:

>> Ch 1 on 141.375 MHz was the one from Mendip. I can't remember the
>> exact frequency of Ch 2 which was used from other locations, but it was
>> in the same ball-park.
>
> Thanks, I wasn't sure about that.

I've found it during a clear out - 141.4625 MHz.
I believe we still pay the licence for that, but it is hardly used
and there was talk of ceasing it.

Local radio (round here anyway) used to use 141.24375, .30625 and .25635
but they are long gone.