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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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  #61  
Old March 10th 17, 01:27 PM posted to uk.tech.digital-tv
external usenet poster
 
Posts: 264
Default why 12V?

On Fri, 10 Mar 2017 12:48:50 -0000
"Woody" wrote:
wrote in message
news
On Fri, 10 Mar 2017 11:25:14 +0000
Ian Jackson wrote:
In message , d writes
On Fri, 10 Mar 2017 10:34:55 +0000
Graham. wrote:
What are the limits of the US "AM" band? In the distent past I
have
owned sets with CONELRAD markings and I don't recall any extra
tuning
range. I know they use 10kHZ spacing.

Perhaps he means station bandwidth limits - US stations go up to
5Khz whereas
in europe its 4.5. AFAIK the actual band itself is the same width.

US stations are spaced at 10kHz, and Europe are 9.


And divide by 2 for each sideband you get a max bandwidth of 5 and
4.5Khz
respectively.


Actually not. There is a 1KHz guard space between slots, so the 9KHz
stepping is actually 8KHz of bandwidth.

In practice the audio response above 3K5Hz so was rolled quite steeply
off so the chances of adjacent channel interference were in theory
reduced.


Maybe in europe, but in the USA the AM stations had noticably better
fidelity than those in the UK when I was last there. Perhaps it was simply
better recievers or perhaps they're not so bothered about adjacent channel
interference especially given the AM stereo system they tried out which IIRC
required even more bandwidth.

--
Spud

  #62  
Old March 10th 17, 01:30 PM posted to uk.tech.digital-tv
external usenet poster
 
Posts: 264
Default why 12V?

On Fri, 10 Mar 2017 14:08:54 +0000
Ian Jackson wrote:
However, AIUI, in the USA, stations in the same area are spaced at least
20kHz apart, and this allows the audio spectrum to be the full 5kHz (or
even increased somewhat) while not causing undue sideband spatter over
far-off stations that are only 10kHz away. Whether modern


That makes sense.

cheap-and-cheerful MW receivers are capable of making use of a bit wider
audio is questionable.


Given digital tuners are switchable between 9 & 10Khz stepping, one would
assume in a decent set it would have switchable filters too.

--
Spud


  #63  
Old March 10th 17, 03:50 PM posted to uk.tech.digital-tv
Woody[_5_]
external usenet poster
 
Posts: 1,659
Default why 12V?


wrote in message
news
On Fri, 10 Mar 2017 12:48:50 -0000
"Woody" wrote:
wrote in message
news
On Fri, 10 Mar 2017 11:25:14 +0000
Ian Jackson wrote:
In message , d
writes
On Fri, 10 Mar 2017 10:34:55 +0000
Graham. wrote:
What are the limits of the US "AM" band? In the distent past I
have
owned sets with CONELRAD markings and I don't recall any extra
tuning
range. I know they use 10kHZ spacing.

Perhaps he means station bandwidth limits - US stations go up to
5Khz whereas
in europe its 4.5. AFAIK the actual band itself is the same
width.

US stations are spaced at 10kHz, and Europe are 9.

And divide by 2 for each sideband you get a max bandwidth of 5 and
4.5Khz
respectively.


Actually not. There is a 1KHz guard space between slots, so the 9KHz
stepping is actually 8KHz of bandwidth.

In practice the audio response above 3K5Hz so was rolled quite
steeply
off so the chances of adjacent channel interference were in theory
reduced.


Maybe in europe, but in the USA the AM stations had noticably better
fidelity than those in the UK when I was last there. Perhaps it was
simply
better recievers or perhaps they're not so bothered about adjacent
channel
interference especially given the AM stereo system they tried out
which IIRC
required even more bandwidth.


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.


--
Woody

harrogate3 at ntlworld dot com


  #65  
Old March 10th 17, 04:26 PM posted to uk.tech.digital-tv
Graham.[_12_]
external usenet poster
 
Posts: 381
Default why 12V?

On Fri, 10 Mar 2017 17:21:50 +0000, Graham.
wrote:

On Fri, 10 Mar 2017 14:30:25 +0000 (UTC), d wrote:

On Fri, 10 Mar 2017 14:08:54 +0000
Ian Jackson wrote:
However, AIUI, in the USA, stations in the same area are spaced at least
20kHz apart, and this allows the audio spectrum to be the full 5kHz (or
even increased somewhat) while not causing undue sideband spatter over
far-off stations that are only 10kHz away. Whether modern


That makes sense.

cheap-and-cheerful MW receivers are capable of making use of a bit wider
audio is questionable.


Given digital tuners are switchable between 9 & 10Khz stepping, one would
assume in a decent set it would have switchable filters too.


While this is all very interesting, J.B.G suggested it was the entire
band that is wider, not a given channel.***

This Wikipeadia entry suggests he is correct
https://en.wikipedia.org/wiki/Medium_wave

On 15 May 1923, Commerce Secretary Herbert Hoover announced a new
bandplan which set aside 81 frequencies, in 10 kHz steps, from 550 kHz
to 1350 kHz (extended to 1500, then 1600 and ultimately 1700 kHz in
later years).
So it would appear the US uses 550 - 1700kHz vs ROW
These would appear to be carrier frequencies, not band edges.


***Correction:
I should have said "not *just* a given channel"
--

Graham.
%Profound_observation%
  #66  
Old March 10th 17, 04:53 PM posted to uk.tech.digital-tv
Graham.[_12_]
external usenet poster
 
Posts: 381
Default why 12V?

On Fri, 10 Mar 2017 16:50:46 -0000, "Woody"
wrote:


wrote in message
news
On Fri, 10 Mar 2017 12:48:50 -0000
"Woody" wrote:
wrote in message
news On Fri, 10 Mar 2017 11:25:14 +0000
Ian Jackson wrote:
In message , d
writes
On Fri, 10 Mar 2017 10:34:55 +0000
Graham. wrote:
What are the limits of the US "AM" band? In the distent past I
have
owned sets with CONELRAD markings and I don't recall any extra
tuning
range. I know they use 10kHZ spacing.

Perhaps he means station bandwidth limits - US stations go up to
5Khz whereas
in europe its 4.5. AFAIK the actual band itself is the same
width.

US stations are spaced at 10kHz, and Europe are 9.

And divide by 2 for each sideband you get a max bandwidth of 5 and
4.5Khz
respectively.


Actually not. There is a 1KHz guard space between slots, so the 9KHz
stepping is actually 8KHz of bandwidth.

In practice the audio response above 3K5Hz so was rolled quite
steeply
off so the chances of adjacent channel interference were in theory
reduced.


Maybe in europe, but in the USA the AM stations had noticably better
fidelity than those in the UK when I was last there. Perhaps it was
simply
better recievers or perhaps they're not so bothered about adjacent
channel
interference especially given the AM stereo system they tried out
which IIRC
required even more bandwidth.


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. There was a weak Eastern European station co-channel, and as
there was no 1KHz heterodyne, this must have moved up at the same
time.

That's not to say there weren't asymmetric sidebands, I have read at
least one account by someone who was there that there were, but
whether this was achieved by deliberate filtering or a slightly off
resonance antenna, I don't know.

Whatever the truth is, it seems that a lot of people would have had a
period of 1KHz discrepancy in their tuning giving exaggerated "top"
and sibilance to the audio, In much the same way as Droitwich's
sojourn from 200 to 198 KHz did.


--

Graham.
%Profound_observation%
  #68  
Old March 10th 17, 08:19 PM posted to uk.tech.digital-tv
Vir Campestris
external usenet poster
 
Posts: 360
Default why 12V?

On 09/03/2017 21:36, charles wrote:
In article , Vir
Campestris wrote:
On 08/03/2017 12:44, The Other John wrote:
On Wed, 08 Mar 2017 11:43:12 +0000, NY wrote:

And why is the standard film frame rate 24?

Was it set by the Merkins? If so could it be because of their 60Hz
mains? You would get 5 positive and negative mains peaks per frame if
my sums are right, thus avoiding strobing effects.

Merkin TV is of course (almost exactly) 30Hz.


It was once, but with the arrival of color it became 59.94Hz

Depends whether you count the interlaced halves as separate frames.

AFAIK it was never 30p, but was filmed at 29.97 or whatever it is and
then transmitted interlaced.

Andy

  #69  
Old March 11th 17, 02:15 AM posted to uk.tech.digital-tv
Johnny B Good[_2_]
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Posts: 387
Default why 12V?

On Fri, 10 Mar 2017 17:21:50 +0000, Graham. wrote:

On Fri, 10 Mar 2017 14:30:25 +0000 (UTC), d wrote:

On Fri, 10 Mar 2017 14:08:54 +0000 Ian Jackson
wrote:
However, AIUI, in the USA, stations in the same area are spaced at
least 20kHz apart, and this allows the audio spectrum to be the full
5kHz (or even increased somewhat) while not causing undue sideband
spatter over far-off stations that are only 10kHz away. Whether modern


That makes sense.

cheap-and-cheerful MW receivers are capable of making use of a bit
wider audio is questionable.


Given digital tuners are switchable between 9 & 10Khz stepping, one
would assume in a decent set it would have switchable filters too.


While this is all very interesting, J.B.G suggested it was the entire
band that is wider, not a given channel.

This Wikipeadia entry suggests he is correct
https://en.wikipedia.org/wiki/Medium_wave


I should bloody well hope so! :-)

I know the MW band covers close to a 3:1 frequency range in the UK and
Europe but I thought I'd best verify the exact ratio used by checking
with wikipedia which also revealed that the Yanks now benefit from an
additional 100KHz tacked on at the HF end (I was already aware of the 9
and 10 KHz transmitter channel spacings).

Since the resonant frequency of a tuned circuit made up of discrete L
and C components varies according to the square root of the LC product,
relatively small variations in the frequency range expected to be covered
by tuning with either just the L or the C component requires that the
ratio of adjustment of either the L or the C component alone has to be
the square of the ratio of the band edge frequencies. For example to tune
a range with a 3.162 ratio requires a 10:1 ratio in the range of
adjustment of either the variable capacitor or inductor chosen to effect
tuning of the radio across the frequency band in question.

My point was that with such a wide ratio of tuning capacitance, it would
have the unfortunate effect of desensitizing the LF end of the MW band if
the aerial tuning circuit was tuned using a variable capacitor. The
variable inductor tuning method (permeability tuning) neatly eliminates
this effect, hence the reason for its use in AM car radios in preference
to a tuning capacitor.

--
Johnny B Good
  #70  
Old March 11th 17, 11:35 AM posted to uk.tech.digital-tv
Ashley Booth[_2_]
external usenet poster
 
Posts: 90
Default why 12V?

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!!

--


---
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