On 20/02/2014 15:08, gareth wrote:
"AndyW" wrote in message
...
On 20/02/2014 11:51, gareth wrote:
"AndyW" wrote in message
...
On 19/02/2014 09:32, gareth wrote:
LED or nitro-benzine as the polariser?
Polariser?
To my eternal regret, because I disposed of them 38 years ago, I had a
pile of "Amateur Wireless" from the 1930s within which were designs
for mirror-drum scanners, and the modulation was not by a neon light
but with a constant light source which was then modulated by a series
of polarising filters, with one being variable to rotate the
polarisation.
ISTR (38 years ago!!!) that the liquid used was nitro-benzene
OK I follow you now. I had a quick google and found out about nitrobenzene
and modulating polarisation. Never heard of it before. Live and learn.
My original set up was as simple and agricultural as they come, vinyl LP,
scrap motor from a cassette player, Neon attached to am amplifier behind
the 'screen' and a camera made from a lens and an LDR recording onto a
cassette player - the bandwidth was low enough to record on audio.
My latest televisor was made from a circle of black plastic spinning on a
hand fan with a very small torch behind it modulated by the sound from a
small mp3 player. It all folds up and fits in a pocket.


Wow! How many lines and frames / sec?

64 lines of low definition glory, I could not tell you of the frames per
second as I use the same TV as a camera by using the same disk, once the
frame starts are synced it works fine. The syncing is carried out by the
highly technical method of slowing the fan with an index finger.


Andy

"AndyW" wrote in message
...
On 20/02/2014 15:08, gareth wrote:
"AndyW" wrote in message
...
On 20/02/2014 11:51, gareth wrote:
"AndyW" wrote in message
...
On 19/02/2014 09:32, gareth wrote:
LED or nitro-benzine as the polariser?
Polariser?
To my eternal regret, because I disposed of them 38 years ago, I had a
pile of "Amateur Wireless" from the 1930s within which were designs
for mirror-drum scanners, and the modulation was not by a neon light
but with a constant light source which was then modulated by a series
of polarising filters, with one being variable to rotate the
polarisation.
ISTR (38 years ago!!!) that the liquid used was nitro-benzene
OK I follow you now. I had a quick google and found out about
nitrobenzene
and modulating polarisation. Never heard of it before. Live and learn.
My original set up was as simple and agricultural as they come, vinyl
LP,
scrap motor from a cassette player, Neon attached to am amplifier behind
the 'screen' and a camera made from a lens and an LDR recording onto a
cassette player - the bandwidth was low enough to record on audio.
My latest televisor was made from a circle of black plastic spinning on
a
hand fan with a very small torch behind it modulated by the sound from a
small mp3 player. It all folds up and fits in a pocket.


Wow! How many lines and frames / sec?

64 lines of low definition glory, I could not tell you of the frames per
second as I use the same TV as a camera by using the same disk, once the
frame starts are synced it works fine. The syncing is carried out by the
highly technical method of slowing the fan with an index finger.


Picking up on your BW comment, AIUI, the Baird transmssions of 30 line
pictures
were also of the audio BW, and were transmitted as part of the normal
broadcast,
but not at the same time as the audio; it was either speech or video, but
not
simultaneously!

On 24/02/2014 08:12, gareth wrote:

Picking up on your BW comment, AIUI, the Baird transmssions of 30 line
pictures
were also of the audio BW, and were transmitted as part of the normal
broadcast,
but not at the same time as the audio; it was either speech or video, but
not
simultaneously!

I read that.
You would think that it would be trivial to transmit on 2 channels; one
for the video and one for the sound.

The bloke who invented thermal socks should have thought of that.

Andy

"AndyW" wrote in message
...
On 24/02/2014 08:12, gareth wrote:
Picking up on your BW comment, AIUI, the Baird transmssions of 30 line
pictures
were also of the audio BW, and were transmitted as part of the normal
broadcast,
but not at the same time as the audio; it was either speech or video, but
not
simultaneously!

I read that.
You would think that it would be trivial to transmit on 2 channels; one
for the video and one for the sound.


Not at that time, when what most people could afford was a blooper,
although admittedly it was probably the rich who could afford Baird
Televisors
and therefore could have stretched to another set for a second channel.

On Tue, 25 Feb 2014, AndyW wrote:

On 24/02/2014 08:12, gareth wrote:

Picking up on your BW comment, AIUI, the Baird transmssions of 30 line
pictures
were also of the audio BW, and were transmitted as part of the normal
broadcast,
but not at the same time as the audio; it was either speech or video, but
not
simultaneously!

I read that.
You would think that it would be trivial to transmit on 2 channels; one for
the video and one for the sound.

But at the time, it would have been expensive, another receiver for the
second channel, two transmitters at the transmitting end. And wasn't it
the era of silent films, or at least silent films weren't that long in the
past? "Who needs the hear sound while watching a picture?"

Much later, some used ISB (independent sideband) to send SSTV and have
audio at the same time. Audio on one sideband, the SSTV signal on the
other. But that's even worse, two whole receivers and two whole
transmitters at both ends, all that selectivity and stability that
wouldn't have been available earlier.

Michael


The bloke who invented thermal socks should have thought of that.

Andy

"Michael Black" wrote in message
xample.org...
On Tue, 25 Feb 2014, AndyW wrote:
On 24/02/2014 08:12, gareth wrote:
Picking up on your BW comment, AIUI, the Baird transmssions of 30 line
pictures
were also of the audio BW, and were transmitted as part of the normal
broadcast,
but not at the same time as the audio; it was either speech or video,
but
not
simultaneously!
I read that.
You would think that it would be trivial to transmit on 2 channels; one
for the video and one for the sound.
But at the time, it would have been expensive, another receiver for the
second channel, two transmitters at the transmitting end. And wasn't it
the era of silent films, or at least silent films weren't that long in the
past? "Who needs the hear sound while watching a picture?"
Much later, some used ISB (independent sideband) to send SSTV and have
audio at the same time. Audio on one sideband, the SSTV signal on the
other. But that's even worse, two whole receivers and two whole
transmitters at both ends, all that selectivity and stability that
wouldn't have been available earlier.

TX could have been simpler had they combined audio and video using
quadrature modulation and a pilot tone, much as is / was used for the
colour subcarrier in PAL (also NTSC?) TV, but I doubt that anyone,
even the filthy rich (or even those who like to boast about how rich
they are :-) ), could have afforded the concomitant RX complexity
on their household budgets!

And talking of colour TV encoding, ISTR ...

NTSC - Never Twice the Same Colour

SECAM - System Essentially Contrary to the American Method

PAL - Peace At last!

BUT, didn't Logie Baird (not to be confused with Yogi Bear :-) )
do some experimentation with colour TV on the mechanical approach
anyway?

On 25/02/2014 16:00, gareth wrote:

BUT, didn't Logie Baird (not to be confused with Yogi Bear :-) )
do some experimentation with colour TV on the mechanical approach
anyway?

He did indeed produce colour TV, and the video recorder and, of course,
thermal socks.

Andy

"AndyW" wrote in message
...
On 25/02/2014 16:00, gareth wrote:

BUT, didn't Logie Baird (not to be confused with Yogi Bear :-) )
do some experimentation with colour TV on the mechanical approach
anyway?

He did indeed produce colour TV, and the video recorder and, of course,
thermal socks.

That Baird was living and working in a largely pre-techincal age, puts to
shame
all those grown-ups of today who exist with beginners' licences; especially
where those
licences are targetted at the 5-year-old.