Which pips?

In article , tony sayer

wrote:
In article , Jim Lesurf
scribeth thus
In article , Bill Wright
wrote:
Phil Cook wrote:
On 10/09/2013 20:42, Bill Wright wrote:
Phil Cook wrote:
On 10/09/2013 18:41, Scott wrote:
On Mon, 09 Sep 2013 17:10:28 -0500, "Steve Thackery"


Surely the propagation delays on FM would be the same as AM?

No, they're much shorter waves. Think about a sausage dog running.

They may be shorter waves but they come much more often so the
speed over the ground is the same, round about C if my physics
doesn't fail me.

It doesn't make any difference how often they come.

Actually, it may. Two reasons occurred to me when I read the above.

1) The refractive index of air tends to rise with frequency though the
range up to about 30GHz. So FM will propagate though the air at a
slightly lower velocity than LF.

2) Near the ground the waves may also be slowed down by the ground
impedance. I'd expect LF to extend further into the ground.

I'd assume both effects are pretty small in this context. But I've
never actually worked out any of the delays for FM v LF.

Those delays will be in the noise compared to the digital distribution
delays Jim, all that coding and decoding and digital propagation delays
etc...

Happy to accept that. I was just pointing out that it'd occurred to me that
"It doesn't make any difference" may not be completely true.

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

tony sayer wrote:

Those delays will be in the noise compared to the digital distribution
delays Jim, all that coding and decoding and digital propagation delays
etc...

Yeah... it's interesting though.

Bill

On 2013-09-13, Dave Saville wrote:
On Fri, 13 Sep 2013 11:27:13 UTC, David Taylor
wrote:

How does that work for cars with electric handbrakes?


There is still a manual switch - Although I think that one cannot do
handbrake turns :-) On my Citroen it would seem that over a certain
speed it does not apply as shortly after we had the car my wife pulled
it on trying to open the arm rest without looking - nothing happened
IIRC - we were on a motorway at the time.

That's what I meant -- I drove an Astra with an electric handbrake for
a while and I don't think it would apply when it was moving. So how
do you do the brake test with an electric handbrake?

--
David Taylor

David Taylor wrote:

That's what I meant -- I drove an Astra with an electric handbrake for
a while and I don't think it would apply when it was moving. So how
do you do the brake test with an electric handbrake?

They stand it on the rolling road, apply the handbrake, and measure the
resistance. I just asked my cousin who runs an MOT garage.

Bill

In article ,
David Taylor wrote:
That's what I meant -- I drove an Astra with an electric handbrake for
a while and I don't think it would apply when it was moving. So how
do you do the brake test with an electric handbrake?

The car isn't moving during an MOT brake test. Only the pair of wheels
being tested. If the brakes couldn't be tested for whatever reason, it
would fail.

--
*When chemists die, they barium.*

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 13 Sep 2013 16:09:42 +0100, Bill Wright
wrote:

David Taylor wrote:

That's what I meant -- I drove an Astra with an electric handbrake for
a while and I don't think it would apply when it was moving. So how
do you do the brake test with an electric handbrake?

They stand it on the rolling road, apply the handbrake, and measure the
resistance. I just asked my cousin who runs an MOT garage.

Bill

I can confirm that. Here in Northern Ireland the MOT tests are the same
but they are done by a government agency rather than private garages.
The owner of the car (or someone on his/her behalf) drives the car into
the testing building and stays in the driver's seat for the first tests
which are the emission measurements. The driver then moves the car to
where the lights are checked, switching lights on and off as instructed
by the vehicle examiner. The examiner then takes over and drives the car
on to the rolling road and does the various brake tests with the owner
in the passenger seat. The owner gets out of the car before the examiner
puts it on the hoist to look at the underside.


--
Peter Duncanson
(in uk.tech.digital-tv)

In article ,
Peter Duncanson wrote:
I can confirm that. Here in Northern Ireland the MOT tests are the same
but they are done by a government agency rather than private garages.
The owner of the car (or someone on his/her behalf) drives the car into
the testing building and stays in the driver's seat for the first tests
which are the emission measurements. The driver then moves the car to
where the lights are checked, switching lights on and off as instructed
by the vehicle examiner. The examiner then takes over and drives the car
on to the rolling road and does the various brake tests with the owner
in the passenger seat. The owner gets out of the car before the examiner
puts it on the hoist to look at the underside.

That used to be the case here - the driver staying in the car to do
various tasks under the control of the MOT tester. But not now. You are
rarely let beyond the MOT waiting room. Probably to do with insurance.

--
*The only difference between a rut and a grave is the depth.

Dave Plowman London SW
To e-mail, change noise into sound.

"Jim Lesurf" wrote in message
...
In article , tony sayer

wrote:
In article , Jim Lesurf
scribeth thus
In article , Bill Wright
wrote:
Phil Cook wrote:
On 10/09/2013 20:42, Bill Wright wrote:
Phil Cook wrote:
On 10/09/2013 18:41, Scott wrote:
On Mon, 09 Sep 2013 17:10:28 -0500, "Steve Thackery"


Surely the propagation delays on FM would be the same as AM?

No, they're much shorter waves. Think about a sausage dog running.

They may be shorter waves but they come much more often so the
speed over the ground is the same, round about C if my physics
doesn't fail me.

It doesn't make any difference how often they come.

Actually, it may. Two reasons occurred to me when I read the above.

1) The refractive index of air tends to rise with frequency though the
range up to about 30GHz. So FM will propagate though the air at a
slightly lower velocity than LF.

2) Near the ground the waves may also be slowed down by the ground
impedance. I'd expect LF to extend further into the ground.

Not very! You have to use very low frequencies just to be receivable a
short distance underwater: -
http://en.wikipedia.org/wiki/Very_lo...tion_met hods


I'd assume both effects are pretty small in this context. But I've
never actually worked out any of the delays for FM v LF.

Those delays will be in the noise compared to the digital distribution
delays Jim, all that coding and decoding and digital propagation delays
etc...

Happy to accept that. I was just pointing out that it'd occurred to me
that
"It doesn't make any difference" may not be completely true.

A bit like Newtonain mechanics is not the whole story Einstein! Even then
Special Relativity was not the whole story either...


Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics
http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article ,
R. Mark Clayton wrote:

"Jim Lesurf" wrote in message
...


Happy to accept that. I was just pointing out that it'd occurred to me
that "It doesn't make any difference" may not be completely true.

A bit like Newtonain mechanics is not the whole story Einstein! Even
then Special Relativity was not the whole story either...

Nor is General Relativity. :-)

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

On Monday, September 9, 2013 10:26:38 PM UTC+1, Another John wrote:
I'm sure this has been asked many times before, but I haven't seen it

....



I had both my digital radio and my FM radio on this teatime, in

different rooms. At 6pm The Pips were broadcast. Given that digital is

always out of synch with FM -- which is the more accurate time signal?





Come to think of it I have another question, related, and equally dumb.

Given that digital is digital, and therefore completely under the

control of the broadcasters (as opposed to the 'organic' FM signal), why

in the name of all that's holy do "they" not synchronise the football

commentary over digital radio, so that it matches TV coverage of the

game? It's bloody annoying hearing about a goal several seconds before

(or sometimes after?) it happens!



John


Its a little optimistic to credit broadcasters with being "in control" of the timing with digital broadcasts - they are not. Different receiver chip sets will have subtle differences in their performance in respect of the decode delay, as will the codecs used by the broadcasters to code the programmes. In analogue systems propagation and distribution causes delay, but these will be predictable and understood. BBC national FM stations are distributed around the country digitally using NICAM, this will introduce a predictable (small) delay, but the network transport that this sits on (C&W MPLS?) will present small amounts of unpredictable latency.

Whils the 198KHz signal broadcast from Droitwich was (is still?) recognised as a standard frequency transmission, the Radio 4 time signal (GTS pips) were never considered a standard time transmission, due to signal processing in BH, signal path delay from BH to Droitwich, and a very unpredictable delay in the old style analogue PO carrier phantoms (slower in hot weather) carrying the raw pips from the Royal Greenwich Observatory's atomic clock at Herstmonceux, Sussex to BH.

What surprises me is that the concept of a time broadcast mechanism wasn't engineered into DAB at mux level. DAB's single frequency networks are so heavily dependent on timing to avoid mutual interference, that GPS references are everywhere. Surely the mux not only could carry an accurate time reference, but a GPS local correction as well!