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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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  #121  
Old March 15th 17, 03:39 PM posted to uk.tech.digital-tv
Andy Burns[_12_]
external usenet poster
 
Posts: 183
Default why 12V?

Max Demian wrote:

I've never managed to persuade a tyre dealer to repair a puncture. They
always decide that it's irreparable for some reason.


Until about 6 years ago I would have said the same, the car I bought at
that time really seemed to be a "puncture magnet" for the first couple
of years I owned it, however they were all repairable either for 15 in
the till or for "a drink" in the tea fund ...

  #122  
Old March 15th 17, 06:57 PM posted to uk.tech.digital-tv
Johnny B Good[_2_]
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Posts: 336
Default why 12V?

On Sat, 11 Mar 2017 18:55:18 +0000, charles wrote:

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!.


And, remember this well! It happened at a time when the industry still
gave a **** for their customers' needs. Indeed, to the extent of being
important enough to be a primary consideration. This meant that the
decisions were driven not only by 'least cost' to the industry itself but
also to their end users.

IOW, "Backwards Compatibility" in order to avoid ****ing off millions of
existing end users was still regarded as "A Prime Directive", unlike
today's rather cavalier attitude to the end user whose status as a
"Valued Customer" is now relegated to that of "Hapless Consumer" to be
treated as the Consumer/Media Industry's "Plaything" (aka, Cash Cow).

A change in attitude that I've no doubt must surely have been prompted
by the successes of the likes of Microsoft's and Apple's marketing
strategies demonstrating that people no longer count as "Valued
Customers" any more in this "Brave New Consumeristic World" of our very
own making.

Those of us old enough to know better, wishing to point the finger of
blame for this sad state of affairs that we all now face, need only to
stand in front of a mirror to confront their Nemesis (a Nemesis which may
at best simply regard such confrontation as that of a "Party Pooper"
assuming such a suggestion to self criticise were to be taken literally).

--
Johnny B Good
  #123  
Old March 15th 17, 06:58 PM posted to uk.tech.digital-tv
Johnny B Good[_2_]
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Posts: 336
Default why 12V?

On Tue, 14 Mar 2017 14:46:15 +0000, Graham. wrote:

On Mon, 13 Mar 2017 17:15:29 -0700 (PDT), "R. Mark Clayton"
wrote:

On Monday, 13 March 2017 12:55:41 UTC, wrote:
On Tuesday, 7 March 2017 20:37:01 UTC, wrote:
So many things run on 12V DC. Firstly, why has that become the
standard?
Is it all because of the nominal voltage of a car battery?
Secondly, wouldn't 24 or 48V be more convenient for many things?

I heard a few years back something about new cars being 48V in the
near future. Did it ever happen?

Bill

+24v DC is used as the de facto standard for LV industrial controls,
such as robots, logic controllers, relays etc. Many controls
companies (such as Siemens) produce SMPSs with +24v DC output.

I recall that some car manufacturers making cars with lots of
electrical gizmos such as high end Mercs were thinking of using 42V as
a way of increasing the overall electrical energy available.


Weight and cost of the wiring rather more.


MR


First they came for our spare wheels, and I did not speak out-
Then they came for our copper...


I reckon that warrants a 'Smiley' :-)


--
Johnny B Good
  #124  
Old March 15th 17, 07:17 PM posted to uk.tech.digital-tv
Woody[_5_]
external usenet poster
 
Posts: 1,581
Default why 12V?


"R. Mark Clayton" wrote in message
...
On Tuesday, 14 March 2017 15:30:13 UTC, wrote:
On Tue, 14 Mar 2017 15:13:06 -0000
"NY" wrote:
I would like to see it made mandatory for all cars to be designed
so they
can be fitted with a full-size, full-speed, unlimited-mileage
spare, to
avoid people being stranded half-way through a journey. It should
have the
same tyre as the four running ones, with the only difference being
maybe
steel rather than alloy.


The thing is that tyres tend to be a lot more puncture resistent
these days
than they used to be even a few decades ago when running over some
broken
glass could knacker the thing. Also people had a habit of never
changing
the spare and often you'd have someone change the tyre then carry
on
barrelling down the motorway on tyre way past its use by date and
if its
one mounted under the car both wheel and tyre could have been
subjected to all
sorts of projectile damage over the years.

And then of course, how many people can actually change a spare?
Plus on
motorways and fast A roads its almost suicidal to try.


I changes a near side tyre on the side of the A6 in Stockport in
1978 - very unpleasant.

The last few times I have not been able to get the wheel off either
at all or without borrowing a meter long brace from a garage.


Its called a wrecking bar - for obvious reasons!


--
Woody

harrogate3 at ntlworld dot com


  #125  
Old March 15th 17, 07:40 PM posted to uk.tech.digital-tv
critcher[_6_]
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Posts: 49
Default why 12V?

On 07/03/2017 20:37, Bill Wright wrote:
So many things run on 12V DC. Firstly, why has that become the standard?
Is it all because of the nominal voltage of a car battery?
Secondly, wouldn't 24 or 48V be more convenient for many things?

I heard a few years back something about new cars being 48V in the near
future. Did it ever happen?

Bill


why not???
  #126  
Old March 15th 17, 07:45 PM posted to uk.tech.digital-tv
Johnny B Good[_2_]
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Posts: 336
Default why 12V?

On Tue, 14 Mar 2017 19:12:52 +0000, NY wrote:

"The Other John" wrote in message
news
On Tue, 14 Mar 2017 18:31:47 +0000, charles wrote:

And nowadays with alloy wheels and locking wheel nuts, where is the
correct socket stored?


And alloy wheels need tightening to the correct torque - how many
people carry a torque wrench?


How essential is it that the correct torque is used, as long as you use
roughly the same torque for all the bolts, and tighten them in the order
1,
3, 2, 4 (or any random order other than consecutive 1, 2, 3, 4) to avoid
creating cyclic torque - just as you would for a steel wheel.


Changing the subject, when did cars change from having bolts on the hub
and the wheel fastened on by nuts, to the present system of threaded
holes in the hub and the wheel fastened on by bolts? Some time in the
80s or 90s? What made them change? I much prefer wheel bolts because you
can offer up the wheel and "hang" its centre on the protrusion in the
hub to take the weight, and then rotate it until the holes line up,
whereas with protruding bolts you had to fine-tune the position while
carrying the whole weight of the wheel. Makes you wonder why they ever
used bolts on the hub.


It goes back at least as far as 1965 with my "C Reg" VW Beetle that I'd
bought from one of my parent's neighbours sometime around 1979. :-)

I suspect the use of wheel *bolts* in the case of VW is an inheritance
from at least the end of WW2 and probably earlier during the 1930s
production run of "The People's Car". The VW Beetle was way ahead of its
contemporaries right up into the 60s and 70s, both in design (streamlined
body shape and independent suspension) and the quality of the steel used
in the bodywork[1].


[1] Early in my ownership, I suffered a blow-out due to picking up a
heavy bolt in the rear nearside tyre whilst travelling the Pennine
section of the M62. Said bolt had tried its best to exit via the rear
wheel arch, leaving a fist sized bump which I never bothered to paint
over on account, even years later, you could still see bright steel
underneath the thin patina of rust where the 14 or so coats of paint had
been knocked off.

If I'd had to make a quality of materials comparison using Motorcycle
manufacturers as a metaphor, I'd equate it to being Triumph Motorcycle
versus BSA motorcycle engines. :-)

--
Johnny B Good
  #127  
Old March 18th 17, 06:12 PM posted to uk.tech.digital-tv
Graham.[_12_]
external usenet poster
 
Posts: 334
Default why 12V?

On Wed, 15 Mar 2017 18:58:43 GMT, Johnny B Good
wrote:

On Tue, 14 Mar 2017 14:46:15 +0000, Graham. wrote:

On Mon, 13 Mar 2017 17:15:29 -0700 (PDT), "R. Mark Clayton"
wrote:

On Monday, 13 March 2017 12:55:41 UTC, wrote:
On Tuesday, 7 March 2017 20:37:01 UTC, wrote:
So many things run on 12V DC. Firstly, why has that become the
standard?
Is it all because of the nominal voltage of a car battery?
Secondly, wouldn't 24 or 48V be more convenient for many things?

I heard a few years back something about new cars being 48V in the
near future. Did it ever happen?

Bill

+24v DC is used as the de facto standard for LV industrial controls,
such as robots, logic controllers, relays etc. Many controls
companies (such as Siemens) produce SMPSs with +24v DC output.

I recall that some car manufacturers making cars with lots of
electrical gizmos such as high end Mercs were thinking of using 42V as
a way of increasing the overall electrical energy available.

Weight and cost of the wiring rather more.


MR


First they came for our spare wheels, and I did not speak out-
Then they came for our copper...


I reckon that warrants a 'Smiley' :-)


With the prospect of driverless cars the final stanza is somewhat
obvious.

--

Graham.
%Profound_observation%
  #128  
Old March 23rd 17, 11:44 AM posted to uk.tech.digital-tv
Vir Campestris
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Posts: 342
Default why 12V?

On 14/03/2017 15:13, NY wrote:
It should have the same tyre as the four running ones


There's an assumption.

I don't have the only car with different tyres front and back...

Andy
  #129  
Old March 23rd 17, 01:19 PM posted to uk.tech.digital-tv
Martin[_2_]
external usenet poster
 
Posts: 8,457
Default why 12V?

The author has marked this message not to be archived. This post will be deleted on March 30, 2017.

On Thu, 23 Mar 2017 11:44:49 +0000, Vir Campestris
wrote:

On 14/03/2017 15:13, NY wrote:
It should have the same tyre as the four running ones


There's an assumption.

I don't have the only car with different tyres front and back...


http://www.continental-tires.com/car...irelexikon-3-4

Almost certainly there are people with cars where all four tyres are different.
:-)
--

Martin in Zuid Holland



  #130  
Old March 23rd 17, 01:52 PM posted to uk.tech.digital-tv
Andy Burns[_12_]
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Posts: 183
Default why 12V?

Martin wrote:

Vir Campestris wrote:

NY wrote:

It should have the same tyre as the four running ones


I don't have the only car with different tyres front and back...


http://www.continental-tires.com/car...irelexikon-3-4


In other words, don't mix sizes, speed ratings and tread patterns, and
although we'd like to scare you into buying four of our identical tyres,
the law doesn't let us ...


 



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