terminology

On Thu, 10 Jan 2008 19:45:05 -0000, Bill Wright
wrote:

They should never have run the mines down like they did. Even if they could
import coal cheaper, they should have realised that we need to be
self-sufficient. I'm normally in favour of market forces but in this case
the risks are too great. Look as us now, relying on all sorts of
unscrupulous foreigners for our energy supplies.

And why we squandered all our gas on running power stations I'll never know.
The power stations should have all remained coal powered, then we'd have
enough gas to last 100 years.

That's short-termism for you. Anything to save a couple of quid this year and
to make the person saving it look good.
It's ****ed broadcasting, it's ****ing this country and it'll **** the world.

"Ian Jackson" wrote in message
...
This is strongly reminiscent of a conventional VHF/UHF tap-off line, as
used
in a TV distribution system.
Surely this shouldn't be necessary? What's the range of acceptable
signal
levels for an FM (or DAB) radio? 60dB? 70dB?
--
Ian

It's necessary alright. I'm not sure why you mention the dynamic range of
a
radio's front end, but anyway, the drop values of commonly used taps run
from 35dB to 12dB in 4dB or 5dB steps. The trunk loss on a four way 35dB
tap
is much less than that of a one way 12dB tap, and if the tap values
weren't
stepped the cumulative trunk losses would mean that the line could not be
very long at all.

Bill


Yes, but this isn't the usual CATV situation. I have no real experience of
leaky feeders in tunnels, but I would have thought that the number of
radio signals carried would be relatively small. These could be launched
at a much higher level than in the CATV world. And radio receivers should
work from (say) less than 10uV to at least 10dBmV. That should allow a
60dB loss down the cable without needing repeaters.

As for the feeder, I would guess that the attenuation of leaky feeder will
only be a little higher than the same non-leaky version (similar
dimensions etc). A quick Google shows 2 to 4dB at 100MHz. I haven't (yet)
found any reference to any reference to 'tapered leak' (or whatever
description is appropriate) in order to equalise the radiation as the
signal on the cable gets weaker.

Although I have spent 43 years in CATV, I have never really got involved
in leaky feeders etc. However, it's a well-established technology, so I
supposed it does work, and that they have got the bugs sorted out by now.
However, what I said above could be complete rubbish.


I think we were at cross-purposes. I thought your comments referred to TV
distribution systems (see the first few lines of the quoted section above)
but in fact I now realise that you were referring to leaky feeders.

Bill

"Ian Jackson" wrote in message
...
but this doesn't really answer the question. Yes, these are the minimum
field strengths needed to overcome potential interference in these areas.
What I think was being asked was how much signal does a radio need to give
it's best reception. Certainly stereo tuners tend to need 1mV to give
best
results, although I once had one which went fully quiet with only 300uV.


Are these 'old clunkers'? A quick bit of Googling indicates that some
modern FM radios work down to around 20dBuv (stereo) and 0dBuV (mono). Car
radios are pretty sensitive. And there's a DAB radio which claims -95dBm
(13dBuV). But there's no obvious indication of the maximum levels.

We never allow FM signal levels at the outlets of a distribution system to
exceed 3dBmV. This means that some channels might well be at -15dBmV. I
would expect a normal tuner to work on that level. To be honest I haven't
taken much notice of the results, but no-one ever complains. My own FM
aerial only produces about -25dBmV on BBC Lincs but it sounds OK. The signal
is distributed to several tuners and they are all happy with it except a
very old Sony (so old that that the tuning knob drags a string with the
pointer!). That tuner struggles because of adjacent channel interference,
and it also needs the stereo to be turned off.

On the other hand, I'm very suspicious of the claims that a tuner will
operate on -60dBmV. In fact I know this is ********. I suspect that these
results are obtained by feeding one channel only into the tuner, which is
unrealistic.

Bill

"Dave Plowman (News)" wrote in message
...
Next door have their TV aerial mounted on the frame of the top floor
dormer - and that has a red box on it. It was 'installed' by their
builders. It has clear line of sight to the CP mast about 5 miles away and
I often wondered why they'd fitted an amp. Especially since I've got a 10
dB attenuator on mine.

Hmm . . .

Bill

"Paul Ratcliffe" wrote in message
...
That's short-termism for you. Anything to save a couple of quid this year
and
to make the person saving it look good.
It's ****ed broadcasting, it's ****ing this country and it'll **** the
world.

A grim prospect indeed. Luckily the world will be ****ed by global warming
first, if the Greenies are to be believed.

Bill

On Fri, 11 Jan 2008 13:20:02 -0000, "ChrisM"
wrote:

In message ,
Marky P Proclaimed from the tallest
tower:

On Fri, 11 Jan 2008 02:21:12 -0000, "Bill Wright"
wrote:


"Marky P" wrote in message
...
On Thu, 10 Jan 2008 08:33:21 -0800 (PST), Geo wrote:

This reminds me of a time back in about 1979, my mate worked in the
local Hi-Fi/TV shop. I was in visiting, and playing with the stuff
in the shop when a neighbour of mine came in. He was on about music
centres, and how stupid people must be to buy all this expensive
stereo equipment, he'd made his record player stereo by soldering
(he knew all about technical things) another speaker onto the
existing speaker connections, only cost him a few quid. He seemed
pleased with it.
I did that with an old Dansette. It was suppose to be a stereo
unit with external speaker, but I think a valve had gone, so I just
wired the external speaker to the internal one. Pretty pointless
really. That was my first record player. My brother got me it
second hand in the 70's.

I had an Alba (like a Dansette but cheaper). I fitted a stereo
cartridge and fed the two outputs to (a) a Sinclair transistor amp,
and (b) the gram socket of a pre-war radio. The speakers were
Wharfdale 8" co-axial built into concrete pipes. It all worked
splendidly, or so it seemed at the time. I had to run the Sinclair
off an old car battery because I hadn't got a 12V psu.

I got a mention on the Light Programme because of the apeakers. I
walked tall the next day, I can tell you.

Bill

Something I just remembered! I put two 4 track mono reel to reel
machines side by side to make a stereo one. Put tape spool on first
machine, past the heads of both machines (but avoiding the pinch
roller of the first machine) then onto the take up spool of the second
machine. Set one machine to track 1, second machine to track 2. It
sort of worked.

Marky P.

Wasn't there a noticible delay between the left and right channels as the
tape travelled from one set of heads to the other...?
I'd have thought you'd have got an audible 'echo' effect for anything that
was in the middle of the 'sound stage'(??)

Not if you made the recording on the same system. You need a blank
tape, otherwise there would be a delay in blanking each channel due to
the erase heads being so far apart.

Marky P.

In article ,
Paul Ratcliffe wrote:
On Thu, 10 Jan 2008 21:44:02 -0000, Graham. wrote:

...and yes, I know there is no lead in a lead pencil.

Time to contact Trading Standards I think. Someone's pulling a fast
one...

You'd have to find one stating it was a lead pencil first...

--
*Never miss a good chance to shut up *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Bill Wright wrote:

"Dave Plowman (News)" wrote in message
...
Next door have their TV aerial mounted on the frame of the top floor
dormer - and that has a red box on it. It was 'installed' by their
builders. It has clear line of sight to the CP mast about 5 miles away
and I often wondered why they'd fitted an amp. Especially since I've
got a 10 dB attenuator on mine.

Hmm . . .

Plenty more tricks the same builders got up to. Like knocking some bricks
out between our cellars when they were fitting the central heating - I can
only guess at something to do with getting the pipes into a confined area.
Looking through the hole showed a mass (mess) of pipes directly in line
with it. Some leaking. ;-) And left off a ventilator grille they've
removed elsewhere next door. So rats got in there then through the hole
into this house...

--
*Women who seek to be equal to men lack ambition.

Dave Plowman London SW
To e-mail, change noise into sound.

Graham. wrote:
At that time (early 70s) my area (Scotland
West) was the only one in Scotland still to have open wire routes, so
I trained on it, but never handled it in anger.

They never seem to get that quite right on preserved steam railways do they?
Can you point me to a good website on open wires? I would be intrested
in how they eliminated crosstalk etc.

Transposition poles at regular intervals. The wires were terminated on
either side of the pole and changed position within the group.

"dick" wrote in message
...
Graham. wrote:
At that time (early 70s) my area (Scotland
West) was the only one in Scotland still to have open wire routes, so
I trained on it, but never handled it in anger.

They never seem to get that quite right on preserved steam railways do
they?
Can you point me to a good website on open wires? I would be intrested
in how they eliminated crosstalk etc.

Transposition poles at regular intervals. The wires were terminated on
either side of the pole and changed position within the group.

Highly hypothetical question, but I have wondered how open
wires would cope with ADSL compared with twisted pairs.
They did at least look like proper RF transmission lines.

--
Graham

%Profound_observation%