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uk.tech.digital-tv (Digital TV - General) (uk.tech.digital-tv) Discussion of all matters technical in origin related to the reception of digital television transmissions, be they via satellite, terrestrial or cable. Advertising is forbidden, with no exceptions.

why 12V?



 
 
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  #71  
Old March 11th 17, 01:27 PM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 389
Default why 12V?

On 11 Mar 2017 12:35:31 GMT, "Ashley Booth" wrote:

Johnny B Good wrote:

On Wed, 08 Mar 2017 17:09:58 +0000, Roderick Stewart wrote:

On Wed, 08 Mar 2017 11:42:21 +0000 (GMT), Jim Lesurf
wrote:

I'm not sure how 5V became the standard for USB power.

TTL logic must figure strongly in the answer.

It's a while since I did electronics. Is 5V (or thereabouts)

based on physical properties of the silicon for the transistors
in TTL? I probably knew this at one time...

I'm trying to recall if RTL or DTL used 5Volts. I did briefly use
some RTL/DTL as an undergrad.

Yes they did.

But yes, IIUC the old TTL standard devices tended to be quite
fussy about the rail voltage.

I've always assumed 5V was chosen simply because it's easy to
produce from a 6V battery.

That wasn't the reason. I think 5 volt was chosen because it was a
nice round number and a voltage close enough to the optimum (whatever
that was at the time).

As regards this 'myth of fussiness about rail voltage', there's no
basis in fact for this. Provided the voltage rails were properly
decoupled to suppress noise artefacts and also properly regulated,
the Vcc rail had a tolerance of +/-10% (4.5 to 5.5 volt) range over
which the TTL chips were guaranteed to meet all their specifications
in full.

It's no accident that the 5v rail in the PC, AT and ATX specs all
mandate a +/-5% tolerance to guarantee that the TTL would never be
asked to operate outside of its voltage tolerance limit.

As for burning TTL devices out with excess voltage, they were
specced to withstand a maximum of 7 volts for 10 seconds or less.
That 7 volt limit represents a 40% over-volting event which seems
quite generous considering that they're intended to be powered from a
regulated noise free 5 volt source maintained to a +/-5% tolerance
rather than directly from a set of four AA carbon zinc torch cells.

[1] A specification claim that was mirrored in the cmos versions of
the original TTL logic family - in this case a generously
conservative claim - it needed the 5VSB rail on the 'Silent Assassin'
versions of those infamous Bestec PSUs used in E-Machines PCs, to go
to 8 or 9 volt, usually overnight (unless you were in the habit of
switching the mains power off), before the cmos based chipsets
finally started to fail (in subtle and interesting ways to begin
with).


I have a piece of equipment with a 1 volt supply line!!


I had a Weller soldering gun years ago (basically a shorted turn in a
transformer) that had an un-measurably low voltage on any instrument I
had at the time.


--

Graham.
%Profound_observation%
  #72  
Old March 11th 17, 04:31 PM posted to uk.tech.digital-tv
NY
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Posts: 1,122
Default why 12V?

"Wolfgang Schwanke" wrote in message
news
According to what you read online, there was a beat between the colour
and sound carriers that made the picture unwatchable. They couldn't
move the sound carrier, so they moved the colour carrier to avoid the
beat. Since the relation between colour and b&w signal must remain
fixed for the whole thing to work, the only way to achieve that was to
tweak the entire vision signal slightly downward. In the European
formats the numbers are different, so no beat and no need for a tweak.
It has nothing to do with how the signals are modulated, only their
frequencies.


So it was "only" necessary because of modulation for broadcast (but that's
how TV is distributed so it's rather critical!) and wasn't a problem with
baseband composite video?

Couldn't they have used a different sub-carrier frequency that was still
(n+1)/2 line frequencies (for some integer value of n), so as to move the
colour sub-carrier, when modulated for broadcast, away from the sound
carrier? Aren't the values of n, both for PAL and NTSC, fairly arbitrary
within a range of values, as long as the line-frequency-multiples of the
colour spectrum fit equidistantly between those of the mono signal (hence
the (n+1)/2*line_frequency).

I've not managed to find an explanation of why it was easier to tweak the
frame and line rate slightly rather than chose a different multiple of half
the line rate for the CSC.

  #73  
Old March 11th 17, 05:55 PM posted to uk.tech.digital-tv
charles[_2_]
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Posts: 557
Default why 12V?

In article , NY
wrote:
"Wolfgang Schwanke" wrote in message
news
According to what you read online, there was a beat between the colour
and sound carriers that made the picture unwatchable. They couldn't
move the sound carrier, so they moved the colour carrier to avoid the
beat. Since the relation between colour and b&w signal must remain
fixed for the whole thing to work, the only way to achieve that was to
tweak the entire vision signal slightly downward. In the European
formats the numbers are different, so no beat and no need for a tweak.
It has nothing to do with how the signals are modulated, only their
frequencies.


So it was "only" necessary because of modulation for broadcast (but
that's how TV is distributed so it's rather critical!) and wasn't a
problem with baseband composite video?


Couldn't they have used a different sub-carrier frequency that was still
(n+1)/2 line frequencies (for some integer value of n), so as to move the
colour sub-carrier, when modulated for broadcast, away from the sound
carrier? Aren't the values of n, both for PAL and NTSC, fairly arbitrary
within a range of values, as long as the line-frequency-multiples of the
colour spectrum fit equidistantly between those of the mono signal (hence
the (n+1)/2*line_frequency).


I've not managed to find an explanation of why it was easier to tweak the
frame and line rate slightly rather than chose a different multiple of
half the line rate for the CSC.


I imagine the National Television Systems Committee thought about all sorts
of things and found this to be the easiest solution to implement. It
happened over 60 years ago!.

--
from KT24 in Surrey, England
  #74  
Old March 11th 17, 06:17 PM posted to uk.tech.digital-tv
Mark Carver
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Posts: 7,562
Default why 12V?

On 10/03/2017 17:53, Graham. wrote:
On Fri, 10 Mar 2017 16:50:46 -0000, "Woody"


Is it that they are using a form of vestigial sideband as used by
something from Eire on 252KHz many years ago? In effect the radio is
slightly off tune which results in a perceived improved audio HF
response.


That discussion about Atlantic 252 comes up from time to time. What
seems to have happened is the station started out on 251 KHz for the
first few months then moved onto its advertised frequency later
because of a regulatory change, standardising on a 9kHz channel
spacing.



No, it started on 254 kHz, and moved (along with its co-channel and
adjacent channel neighbours) to 252 a few months after launch, due
to the last acts of the GE75 plan. The upper portion of the LF band,
was rearranged after the lower half, (the move of R4 from 200 to 198 etc)

It was always branded as 'Atlantic 252' from the outset to avoid confusion.

As far a US stations are concerned, their audio fidelity is far in
excess of European ones (IME). I think that there is much wider spacing
between services (both spectrum wise, and geographically !) So although
the channels are in 10 kHz steps, I suspect Tx bandwidth exceeds this.

--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #75  
Old March 11th 17, 06:20 PM posted to uk.tech.digital-tv
Mark Carver
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Posts: 7,562
Default why 12V?

On 10/03/2017 20:37, Ian Jackson wrote:


In any case, no one expects hi-fi from MW AM.


The Japanese had a good stab at it:-

https://www.youtube.com/watch?v=l_ZPx64E5I0


--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #76  
Old March 11th 17, 06:22 PM posted to uk.tech.digital-tv
Mark Carver
external usenet poster
 
Posts: 7,562
Default why 12V?

On 11/03/2017 19:20, Mark Carver wrote:
On 10/03/2017 20:37, Ian Jackson wrote:


In any case, no one expects hi-fi from MW AM.


The Japanese had a good stab at it:-

https://www.youtube.com/watch?v=l_ZPx64E5I0


And

https://www.youtube.com/watch?v=YMAPKTnJtnA


--
Mark
Please replace invalid and invalid with gmx and net to reply.
  #77  
Old March 11th 17, 10:29 PM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 389
Default why 12V?

On Sat, 11 Mar 2017 19:17:51 +0000, Mark Carver
wrote:

On 10/03/2017 17:53, Graham. wrote:
On Fri, 10 Mar 2017 16:50:46 -0000, "Woody"


Is it that they are using a form of vestigial sideband as used by
something from Eire on 252KHz many years ago? In effect the radio is
slightly off tune which results in a perceived improved audio HF
response.


That discussion about Atlantic 252 comes up from time to time. What
seems to have happened is the station started out on 251 KHz for the
first few months then moved onto its advertised frequency later
because of a regulatory change, standardising on a 9kHz channel
spacing.



No, it started on 254 kHz, and moved (along with its co-channel and
adjacent channel neighbours) to 252 a few months after launch, due
to the last acts of the GE75 plan. The upper portion of the LF band,
was rearranged after the lower half, (the move of R4 from 200 to 198 etc)

It was always branded as 'Atlantic 252' from the outset to avoid confusion.

As far a US stations are concerned, their audio fidelity is far in
excess of European ones (IME). I think that there is much wider spacing
between services (both spectrum wise, and geographically !) So although
the channels are in 10 kHz steps, I suspect Tx bandwidth exceeds this.


Thanks Mark. The synthesizer in the car radio that I had at the time
went in 1kHz steps on LW and 9KHz on MW

Do you think the asymmetric sidebands thing is a myth?
A way a person with a little knowledge of how the medium works might
reconcile what he thought was the carrier frequency with how it
sounded when tuning through the channel?

It wasn't just the frequency change that they were economical with the
truth, they never acknowledged their Irish roots on air,
(notwithstanding the accent of their presenters)

They also used to stress the "01" of the "010" international code, no
doubt to suggest to their young audience they were dialling a London
number, albeit with rather too many digits.


--

Graham.
%Profound_observation%
  #78  
Old March 12th 17, 01:53 AM posted to uk.tech.digital-tv
Graham.[_12_]
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Posts: 389
Default why 12V?

On Sun, 12 Mar 2017 01:52:10 +0000, wrote:

On Sat, 11 Mar 2017 23:29:15 +0000, Graham.
wrote:



That discussion about Atlantic 252 comes up from time to time.

It was always branded as 'Atlantic 252' from the outset to avoid confusion.




It wasn't just the frequency change that they were economical with the
truth, they never acknowledged their Irish roots on air,
(notwithstanding the accent of their presenters)


Could that be because of RTE joining up with RTL to establish the
station and initially at least it was regarded as a fresh although
somewhat late attempt for RTL to again cover the UK with a commercial
national music station that they had not done in daytime since the
early 1950's when they removed English programming from long wave.
RTL were the majority shareholder and it was to the evening Luxembourg
service on 208 to which listeners were invited to tune when the
station closed at 7pm in its early days.
Always thought it a bit of a strange decision to do it with ILR
already established by then, if it had been done at the end of the
sixties following the demise of the pirates and before Radio One got
separated from Radio Two it may have got better established.
The name Atlantic 252 even gave a nod to that era though it is more
probable that the recent popularity if not financial success of Laser
558 also had an influence on that name especially as least one
presenter Charlie Wolf had been on that station.

In the end ISTR that the coverage was less successful than hoped with
the signal only really being heard well in the North of Britain which
was awkward for their London office and they had to pay a lot for a
leased line to Ireland to hear the output.


They also used to stress the "01" of the "010" international code, no
doubt to suggest to their young audience they were dialling a London
number, albeit with rather too many digits.


They phoned out heck of a lot in a more modern version of Lobby Lud
AICMFP , happened to my sister when she lived up North .
They rang a random number and said
“What’s the phrase that pays?”
and if you replied
“I listen to Long Wave Radio Atlantic 252” you got some money though
I can't remember how much .

G.Harman


Yes, listening to 252 in London was a bit like receiving Westerglen in
Manchester, when Droitwich is off the air.


--

Graham.
%Profound_observation%
  #79  
Old March 12th 17, 02:57 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
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Posts: 1,746
Default why 12V?

On 12/03/2017 02:53, Graham. wrote:

Yes, listening to 252 in London was a bit like receiving Westerglen in
Manchester, when Droitwich is off the air.


As Hil and I looked round the British Cemetery in Normandy our stroppy
teenage daughter insisted on sitting in the van listening to Atlantic 252.

Bill

  #80  
Old March 12th 17, 09:04 AM posted to uk.tech.digital-tv
Mark Carver
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Posts: 7,562
Default why 12V?

On 12/03/2017 02:53, Graham. wrote:

Yes, listening to 252 in London was a bit like receiving Westerglen in
Manchester, when Droitwich is off the air.


It was bloody marvelous in North West Scotland, the only thing we could
consistently receive on the car radio touring around up there, though
the same 10 records over and over and over and over and over and over
and over and over and over and over and over and over and over and over
and over and over and over again got very tiresome, (Though that's Heart
FM's business model, so it works I assume)



--
Mark
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