FM PLL Demodulation

[[email protected]]

That wasn't even the first IC type. I was seeing them in the early 1970s,
RCA IIRC.


** The first PPL stereo decoder was National Semiconductor's LM1310.

Appeared in about 1975.

It used a simple switching matrix to get L and R outputs.

Was that 1310 originally from NS ?

I used the Motorola MC1310 in the early 1970's.

The only available PLL alternative was the RCA part (3090) which
required IIRC an LC tank at 76 kHz, so without proper test
instruments, I used the MC1310.

Earlier ones were full of horrible tuned circuits.

Bandpass filtering at 19 kHz are quite BIG followed by a frequency
doubler and Big filter at 38 kHz, before entering a diode ring
demodulator.

 

[Phil Allison]

Was that 1310 originally from NS ?

I used the Motorola MC1310 in the early 1970's.

** FM stereo did not reach Australia until December 1974 - 2MBS FM in
Sydney was first on air.

Had my first home brew FM tuner going by mid '75 - with varicap front end
and a large edge meter for frequency read out.

It may well be that the MC1310 decoder was first.



..... Phil

 

[josephkk]

Then it couldn't be the first, i used an RCA PLL type in 1973.

Was that 1310 originally from NS ?

I used the Motorola MC1310 in the early 1970's.

The only available PLL alternative was the RCA part (3090) which
required IIRC an LC tank at 76 kHz, so without proper test
instruments, I used the MC1310.


Bandpass filtering at 19 kHz are quite BIG followed by a frequency
doubler and Big filter at 38 kHz, before entering a diode ring
demodulator.

I don't remember the original part numbers. The RCA part i used had an rc
76 kHz oscillator, no large LC tank at all. The large tank circuits were
real common in all previous generation stereo decoders, i built a few of
those from kits also.

?-)

 

[josephkk]

If you only want to ride through the fade, why not use a suitable
crystal oscillator (VXCO), derive 38/19 kHz from it. Use the 19 kHz to
lock to the pilot tone and put a sample/hold circuit between the phase
detector and VXCO. When the signal strength drops too low, put the S/H
in Hold mode and the VXCO should remain on the correct frequency. When
the RF returns after thee fade, the VXCO is still at correct frequency
and nearly correct phase, thus relocking would happen immediately,
without any bad phase discontinuities.

These days it might even be possible to decode a _strong_ differential
(L-R) DSB signal (23..53 kHz) without the pilot tone using a Costas
loop.

Ummm, no. A Costas loop does not decode FM stereo, but entirely other
signals.
Moreover, by the time the pilot tone is lost the L-R differential
component is long gone.

?-)

 

[[email protected]]

Ummm, no. A Costas loop does not decode FM stereo, but entirely other
signals.

Apparently I was not clear enough, I was referring to the post-FM
detector signal consisting of 0-15 kHz M (mono) signal (L+R), 19 kHz
pilot, the S ("stereo difference") signal (L-R) between 23 and 53 kHz
(DSB) with a suppressed carrier at 38 kHz and 60-74 kHz SCA signal
(USA) or data broadcast at 57 kHz (3x19 kHz ) in Europe.

The Costas loop would be usable for decoding this S-signal.

Moreover, by the time the pilot tone is lost the L-R differential
component is long gone.

?-)

With strong signals, the multipath propagation will act just like a
comb filter, taking out selectively some point frequencies in the
110-300 kHz broadcast signal. This might cause some severe phase shift
to the 19 kHz pilot tone, messing the stereo decoding.

Thus, it might make more sense to use a Costas loop to decode the
S-signal, instead of relying on the 19 kHz pilot, but I have no
practical experience, especially about multipath conditions.

Multipath and weak signals are quite different environments, so
different approaches are justified.

There is a similar situation with satellite broadcasts. While it is
quite easy in analog satellite transmissions to add extra audio-only
subcarriers, the reception requires that the whole 27 MHz (or
whatever) transponder can be received above threshold and _only_then_,
the audio channel can be separated.

Of course, such systems would NOT be useful for mobile audio-only
satellite reception.

 

[Phil Allison]

"David Eather is a Criminal Nutter "

No,

** That is a blatant lie.

A net stalker IS what you are.

Whoever you are.

but you HAVE threated people in the pastAND you have gone so far as to
offer money on USENET for the address of someone you had a grip against.

** YOU have no idea what your are talking about.

There was one anonymous stalker whom I wished to report to the police.

That says you have the potential to be a psycho and the way to try to be
anonymous ..

** ANONYMOUS ???????

My name, address and phone number have been posted many times.

YOU are the one who is anonymous.

Excuse me - you threatened to "kill my entire family if I should ever nit
pick you again".

** Look like a invented quote there.

You lying POS.

And some other poor sod who offended you had to live with you offering
money so you could track him down.

** That poster was a psychopath, I wanted to report his criminal behaviour
on usenet to the police.

YOU have NO idea !!!

I have made no secret about myself.

** OK, what do ( or did) you do for a living ?

Which part of Australia do you live in ?

How old are you ?

I bet you will not answer, or you will supply lies instead.

EVERYTHING you have claimed is FALSE.

You are paranoid, autistic and VERY stupid.





...... Phil

 

[josephkk]

There is a similar situation with satellite broadcasts. While it is
quite easy in analog satellite transmissions to add extra audio-only
subcarriers, the reception requires that the whole 27 MHz (or
whatever) transponder can be received above threshold and _only_then_,
the audio channel can be separated.

Of course, such systems would NOT be useful for mobile audio-only
satellite reception.

Being down under i don't see any reason for you to be familiar with Sirius
or XM radio, both direct satellite digital audio broadcast systems. Not
sure how they do it but it works pretty good here in the USA.


?-)

 

[[email protected]]

Being down under i don't see any reason for you to be familiar with Sirius
or XM radio, both direct satellite digital audio broadcast systems. Not
sure how they do it but it works pretty good here in the USA.

The question really is how many satellite transponders you can afford
to buy.

If you can afford to buy a whole TWT (and associated channel
electronics on a satellite) to just send 1 MHz of bandwidth (instead
of 27 MHz), the receiver at required bandwidth will get a 15 dB
increase in SNR, which in the digital world is a huge advantage.

A few (2-4) independent audio streams could reasonably well be sent
through a standard satellite transponder, but will require a
significant (several dB) backoff of the TWT in order to remain in the
linear region.

As far as I understand, both Sirius and XM use terrestrial gap fillers
in urban areas, where the satellite is not directly visible .

 

[josephkk]

Apparently I was not clear enough, I was referring to the post-FM
detector signal consisting of 0-15 kHz M (mono) signal (L+R), 19 kHz
pilot, the S ("stereo difference") signal (L-R) between 23 and 53 kHz
(DSB) with a suppressed carrier at 38 kHz and 60-74 kHz SCA signal
(USA) or data broadcast at 57 kHz (3x19 kHz ) in Europe.

The Costas loop would be usable for decoding this S-signal.

Repeating myself, the Costas loop signals are NOT useful for decoding the
stereo difference component (S). It can be used to send low speed digital
data on the 19 kHz pilot tone.

 

[Mark]

to the OP George,

Didn't we have this conversation here a few years ago???...

If you want to dig the 19 kHz pilot tone out of the noise, you could
take a standard FM receiver and build an AFC loop around it that has a
BW that will pass most of the audio so that the AFC will "unmodulate"
most of the audio. The resulting signal will be more narrow band so
you can then demodulate that with a more narrow passband IF which will
yield a better SNR on the 19 kHz pilot.

I'm gonna guess you could improve the pre demodulation SNR by 3 to 6
dB depending on how effective you can AFC out the audio.

What I want to know is WHY anyone would want to do this?

Mark