On Sun, 25 Jul 2004 17:13:33 GMT, "Fleetie"
wrote:

"John Phillips" wrote
In article , Keith G wrote:

When FM radio (2 in the evenings often and 3 most of the time) hits the
spot, which it frequently does, it really is the best 'audio' you can get
and is altogether better than any TV or digital sound!

I agree entirely on the superb quality of analogue FM broadcasts when
they do hit the spot.

However, on the subject of "better than any ... digital sound" sorry to
quibble but I believe the UK national "analogue FM" transmtter network
is fed with digital NICAM-encoded content. Assuming I'm right, even
though the transmission is analogue FM the source is still digital.
And what's more it's just 14-bit digital at 32 ksamples/sec before we
even get to the issue of 10-bit NICAM transcoding.

32ks/s (==16kHz bandwidth)? Isn't FM capable of up to 19kHz? ISTR hearing
that, or at least, that the difference signal (?) is stuck up 19kHz above
the main signal.

Yes, it is, which means a 'brick-wall' filter from 15kHz to suppress
the pilot tone, since brick walls weren't so high back in the '50s!
--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article ,
Stewart Pinkerton wrote:
32ks/s (==16kHz bandwidth)? Isn't FM capable of up to 19kHz? ISTR
hearing that, or at least, that the difference signal (?) is stuck up
19kHz above the main signal.

Yes, it is, which means a 'brick-wall' filter from 15kHz to suppress the
pilot tone, since brick walls weren't so high back in the '50s!

Or didn't bother - as Quad with the FM3.

--
*Make it idiot-proof and someone will make a better idiot.

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

In article , Dave Plowman (News)
wrote:
In article , Stewart
Pinkerton wrote:
32ks/s (==16kHz bandwidth)? Isn't FM capable of up to 19kHz? ISTR
hearing that, or at least, that the difference signal (?) is stuck up
19kHz above the main signal.

Yes, it is, which means a 'brick-wall' filter from 15kHz to suppress
the pilot tone, since brick walls weren't so high back in the '50s!

Or didn't bother - as Quad with the FM3.

Afraid I am not sure what you mean. The diagrams and descriptions I have
for the FM3 show third-order (?) LP filters after the output from the 1310
stereo decoder. These follow the time-contants which also tend to roll
down HF. Do you mean something else, or an earlier tuner?

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article ,
Jim Lesurf wrote:
Or didn't bother - as Quad with the FM3.

Afraid I am not sure what you mean. The diagrams and descriptions I have
for the FM3 show third-order (?) LP filters after the output from the
1310 stereo decoder. These follow the time-contants which also tend to
roll down HF. Do you mean something else, or an earlier tuner?

It caused 'whistles' on both my 1/4" tape machines by beating with the
bias. I ended up adding a Toko filter that you mentioned earlier. Mine is
a very early FM3, though.

--
*The first rule of holes: If you are in one, stop digging!

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

Dave Plowman (News) wrote:
In article ,
Jim Lesurf wrote:
Or didn't bother - as Quad with the FM3.

Afraid I am not sure what you mean. The diagrams and descriptions I
have for the FM3 show third-order (?) LP filters after the output
from the 1310 stereo decoder. These follow the time-contants which
also tend to roll down HF. Do you mean something else, or an earlier
tuner?

It caused 'whistles' on both my 1/4" tape machines by beating with the
bias. I ended up adding a Toko filter that you mentioned earlier.
Mine is a very early FM3, though.


Hence the MPX (mulitplex) filters on tape decks - those which don't have a
switch generally have it on all the time. Which reminds me, must get my
cassette deck fixed one day...


--
slightly greasy solar atoms...

In article ,
Tim S Kemp wrote:
It caused 'whistles' on both my 1/4" tape machines by beating with the
bias. I ended up adding a Toko filter that you mentioned earlier. Mine
is a very early FM3, though.


Hence the MPX (mulitplex) filters on tape decks - those which don't have
a switch generally have it on all the time. Which reminds me, must get
my cassette deck fixed one day...

Given that it's not an audio signal, it's the job of the tuner to remove
it. Filtering the input to a tape machine is fine if it's switchable, but
not, given that it's within the audible range. Assuming the tape machine
is capable of recording and reproducing it, of course.

--
*Yes, I am an agent of Satan, but my duties are largely ceremonial

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

In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:
Or didn't bother - as Quad with the FM3.

Afraid I am not sure what you mean. The diagrams and descriptions I
have for the FM3 show third-order (?) LP filters after the output from
the 1310 stereo decoder. These follow the time-contants which also
tend to roll down HF. Do you mean something else, or an earlier tuner?

It caused 'whistles' on both my 1/4" tape machines by beating with the
bias. I ended up adding a Toko filter that you mentioned earlier. Mine
is a very early FM3, though.

I can't recall details off-hand, but I think that the Toko filters tended
to be higher order than 3rd.[1] Hence they probably suppress the 38kHz,
etc, more efficiently than the simple active filters in the FM3. Also, for
all I know, early FM3's may not have had the same filter arrangement as in
the circuit I have.

FWIW with the same decoder IC, the Armstrong 600 used the Toko filters.
They just 'did the job' as passive cans we just bought and fitted with no
need to twiddle or align values. Making up your own filters was a pain for
various reasons. Not surprising that Toko and Alps ended up being the guts
of many UK tuners. :-)

[1] My memory is saying 6th or 8th, but that may be incorrect.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , Stewart Pinkerton
wrote:
On Sun, 25 Jul 2004 17:13:33 GMT, "Fleetie"
wrote:


32ks/s (==16kHz bandwidth)? Isn't FM capable of up to 19kHz? ISTR
hearing that, or at least, that the difference signal (?) is stuck up
19kHz above the main signal.

Yes, it is, which means a 'brick-wall' filter from 15kHz to suppress the
pilot tone, since brick walls weren't so high back in the '50s!

IIRC It was common on some of the early stereo decoders to use notch
filters to kill the 19 and/or 38 kHz, combined with a relatively slow lpf.
This was a fiddle to set up for nulling the 19 kHz, but meant you could
avoid having a more demanding design to make on a production line.

Again IIRC the 'Toko' filters that were often used in the 1970's and 80's
also had an alignment that notched down at these frequencies to give
improved 19/38 rejection values without having to have ultra-high brickwall
cutoff for their LP slope.

By way of comparion, an old mono Leak Troughline I have leaks 19, 38, and
indeed, IF, like a sieve from its audio outputs. Filters? What are they?
Its got a time-constant. What more do you want?... 8-]

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html