SCART functions

In article , Ian Jackson wrote:
What I'm dubious about is the American use of 50 ohms for video (well,
certainly good old analogue video - and, in particular, for normal
domestic equipment). However, it may be that 50 ohms has been adopted
for the newer digital formats (of which I know little!).

I thought it was 50 Ohm for RF and 75 Ohm for baseband video. I've seen
lots of picture monitors with switchable terminations, but none of them,
not even the multistandard ones, had anything other than 75 Ohm.

Rod.
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In article , Paul D Smith wrote:
Just a thought, but have you tried setting the PC output to 640x480 which is
about as close to PAL as most laptops can manage? 800x600 also "worked"
(i.e would display) on some old sets.

640x480 VGA has a line frequency of 31.48kHz, so I wouldn't expect a standard
TV to be able to display it.

Rod.
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In message on Thu, 18 Aug 2011 09:36:12 +0100
Jim Lesurf wrote:


Since my interest in audio and FM predated my going to Uni I initially
found the use of 50 Ohms for lab gear the oddity.

I remember wasting a lot of time on a sweep set up for aligning broadband VHF
amplifiers as there was no way I could get the response of the reference trace
flat.

Eventually, after much desperation and head banging, I discovered that the
calibration cable from the Tek scope I was using - 50 ohm BNC to BNC - had
found its way into the test set-up!

--

Terry

In message en.co.uk on Fri,
19 Aug 2011 10:52:55 +0100
Roderick Stewart wrote:

In article , Ian Jackson wrote:
What I'm dubious about is the American use of 50 ohms for video (well,
certainly good old analogue video - and, in particular, for normal
domestic equipment). However, it may be that 50 ohms has been adopted
for the newer digital formats (of which I know little!).

I thought it was 50 Ohm for RF and 75 Ohm for baseband video. I've seen
lots of picture monitors with switchable terminations, but none of them,
not even the multistandard ones, had anything other than 75 Ohm.


I think you'll find that 50 ohm is standard for anything involving
transmission, including transmit/receive, but 75 ohms is the standard for
receive only situations.

IIRC 75 ohm cable offers the best (lowest) attenuation but the thinner centre
conductor means that excessively large cable sizes are needed to carry power.

For this reason, the thicker centre conductor of 50 ohm cable makes it much
better suited to transmission.

I'm sure someone will point to a much better description but that, I believe,
is the basic difference.

--

Terry

On 19/08/2011 12:01, Terry Casey wrote:
I think you'll find that 50 ohm is standard for anything involving
transmission, including transmit/receive, but 75 ohms is the standard for
receive only situations.

IIRC 75 ohm cable offers the best (lowest) attenuation but the thinner centre
conductor means that excessively large cable sizes are needed to carry power.

For this reason, the thicker centre conductor of 50 ohm cable makes it much
better suited to transmission.

Except wireless mic and talkback kit (send and receive) is normally 50
ohms ?

I go with the notion that 75R is the world standard for baseband video,
but RF is still a mixed currency of 75 and 50 ?(for unbalanced feeders )

--
Mark
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In article ,
Terry
Casey wrote:


Eventually, after much desperation and head banging, I discovered that
the calibration cable from the Tek scope I was using - 50 ohm BNC to
BNC - had found its way into the test set-up!

I've tried to keep with choosing white coax for 75 Ohm, and black for 50
Ohm. But despite this I've also ended up with an assortment of grey or
brown coax - most of which is 75 Ohm. So, Entropy Rules, as usual... :-)

Slainte,

Jim

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On Tue, 16 Aug 2011 19:37:26 +0100
Mark Carver wrote:

Davey wrote:
On Tue, 16 Aug 2011 17:24:06 +0100
Mark Carver wrote:

It will be interesting to see what type of output appears when the
set is tuned to an analogue PAL transmission ?

And the answer is:

Full colour!

So, if I read this correctly, the SCART is doing its job,
but the TV set's other internals are not doing what I want them to
do. Since both Freeview and HDMI are Digital, I am not going to be
able to get a colour signal out of the SCART socket of the TV set
with either kind of digital input. Correct?

Correct

I have another set, this one a Samsung, but it is on a different
floor and a real pain to move to where all the other stuff is. But
would it be worth trying it once? It has one SCART socket, one HDMI
socket, and some other stuff that I don't know about, (like the
Toshiba), optical sound or something, which is beyond my
experience. But it does have the rudiments of what I need. Maybe
for the first test I could disconnect the VCR and take that to the
Samsung, to see if that one sends out colour. If it's also B&W,
then that would be the end of testing. Annoyingly, it has phono
sockets, but they are all inputs only.
Thanks for all the help and ideas.

Give it a go, I suspect the same results, but only one way to find
out for sure !



I finally got a window of opportunity, unhooked the VCR and took it
upstairs, and connected just the required ports to the Samsung 19" TV
set. And....
The recording from the SCART port was in wonderful living colour.
So the next thing is to fire off a message to Toshiba asking why their
later-model TV doesn't do this, when Samsung's out-of-date one does?
So to do what I want, I need to either bring the Samsung down to the
living room, or take the VCR and the PC up to the Samsung.

But there's mo
Once the PC-to-VCR-via-HDMI route was active, I was then going to try
to send the A/V signal from the VCR out to a Dazzle A/V-to-PC's-DVD
recorder. Which means that the final path would look something like:

1. PC playing program recorded on HDD, output via HDMI;
2. HMDM input to TV set, SCART-A/V output to VCR;
3. VCR A/V output to Dazzle, which sends via USB to PC's DVD recording
software. Recording on VCR possible, but not necessary.

I think I need a drink, it is Friday afternoon.....
--
Davey.

In message on Fri, 19 Aug 2011 12:14:51 +0100
Mark Carver wrote:

On 19/08/2011 12:01, Terry Casey wrote:
I think you'll find that 50 ohm is standard for anything involving
transmission, including transmit/receive, but 75 ohms is the standard for
receive only situations.

IIRC 75 ohm cable offers the best (lowest) attenuation but the thinner centre
conductor means that excessively large cable sizes are needed to carry power.

For this reason, the thicker centre conductor of 50 ohm cable makes it much
better suited to transmission.

Except wireless mic and talkback kit (send and receive) is normally 50
ohms ?

I said "I think you'll find that 50 ohm is standard for anything involving
transmission, including transmit/receive ..."

I didn't realise that wireless mics don't transmit ...

.... and that talkback is receive only ...!

--

Terry

Terry Casey wrote:


I think you'll find that 50 ohm is standard for anything involving
transmission, including transmit/receive, but 75 ohms is the standard
for
receive only situations.

IIRC 75 ohm cable offers the best (lowest) attenuation but the thinner
centre conductor means that excessively large cable sizes are needed
to
carry power.

For this reason, the thicker centre conductor of 50 ohm cable makes it
much better suited to transmission.

I'm sure someone will point to a much better description but that, I
believe, is the basic difference.

Theoretically the coaxial cable impedance offering the lowest loss for a
fixed outer diameter is 76.9 ohms.

For transmission one might want to choose the cable which is capable of
carrying the highest power. Transmission power of a cable of fixed
outside diameter is ultimately limited by flashover of the insulation,
and the impedance which gives the highest power-carrying ability before
flashover is 60 ohms.

However the curves of loss / power handling don't vary much with
impedance and anything between 50 and 80 ohms is close to optimum.

[Source: Communications Engineering by Everett & Anner, 1956. I used to
understand this stuff...]

Dave

At 14:34:33 Fri, 19 Aug 2011, Davey wrote:

I finally got a window of opportunity, unhooked the VCR and took it
upstairs, and connected just the required ports to the Samsung 19" TV
set. And....
The recording from the SCART port was in wonderful living colour.
So the next thing is to fire off a message to Toshiba asking why their
later-model TV doesn't do this, when Samsung's out-of-date one does?

It would be good to get a reply from Toshiba. You might also ask why
you didn't get the SCART configure option in the Setup menu. I suspect
this will only appear when you have selected an external signal source
(top left button on remote), otherwise, with TV selected, the menu will
show the "Channel" option as you said.

If you can't get to the SCART options, how would you choose between
composite and S-video as the input? I'm not saying this will have any
effect on the output, but it's worth a try.

--
John L