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Old 23rd July 2006, 08:25 AM   #1
latala is offline latala  United Kingdom
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Default sinclair phase lock tuner

I have a abiding interest in Sincliar products. One of his gadgets was the phase locked tuner I have three units all working ! Does any one have a schematic for this as i would like to see how he has done it
Regards Trev
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Old 23rd July 2006, 08:33 AM   #2
AndrewT is online now AndrewT  Scotland
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Hi,
that's going back a bit! 1970/71?
I think it preceeded the phase locked loop used for stereo decoding.

This was phase locked reception, alledgedly adopted from "space communications"
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regards Andrew T.
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Old 23rd July 2006, 11:10 AM   #3
latala is offline latala  United Kingdom
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yes you are dead right ! if only clives products were as good as his claims ?
there are a bno of tuners etc that still use this techneque and I know it still works well
I am as explained a big fan so please anyone !!!
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Old 23rd July 2006, 11:44 AM   #4
AndrewT is online now AndrewT  Scotland
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Hi,
many FM tuners use a phase locked loop (built into a chip) to decode the stereo information in the demodulated signal.

The Sinclair is different.
It uses a phase locked loop to demodulate the signal.
I cannot recall the method for the decoding but it was one of the common methods at that time, but it was not phase locked.
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Old 23rd July 2006, 06:19 PM   #5
latala is offline latala  United Kingdom
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Yes He did an earlier pulse count detector unit ! I also have 1 of those, but does definatlly claim a phase locked demodulator in tha case of the later unit
They were available as part of the project 60 ! and series 2000//3000
regards trev
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Old 20th February 2014, 01:18 PM   #6
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I think that you are talking about the Sinclair Studio 2000 Radio.
The phase locked loop in it works at the IF frequency of 10.7 MHz to convert
the IF modulated signal to the baseband audio.
The Studio 2000 radio used very few discrete coils.
The tuner coils (for operation at 88-108MHz) were tracks on the printed circuit board,
as was the only IF (10.7MHz) tuned transformer.

The remaining IF selectivity was given by the phase locked loop.

I was lucky enough to see one of these radios when they first came out.

As usual, Sinclair had gone a bit too far in cost reducing it.

The printed circuit IF transformer, although covered by a metal screen,
picked up 10.7MHz transmissions, which could sometimes be heard in the background.

As the 10.7MHz phase locked loop used no coils, and gave a linear,
easy to set up output, I duplicated that part of the circuit,
but replaced the IF with a CA3089 and the tuner with a 2 transistor
mechanical tuner to make a cheap radio (I was a student at university then).

How does a phase locked loop (PLL) make an FM discriminator?
Lock it to the IF signal, and the feedback signal to the VCO
(Voltage Controllled Oscillator) of the PLL is the original audio signal.

Sinclair made the whole discriminator with 5 transistors, some resistors,
and one 30pF trimmer - genius.

How is a PLL useful in a stereo decoder for FM radio?

Well, the stereo signal can be looked upon as two audio signal
inputs (the left and right channel signals) being switched by a
fast switch at 38KHz, selecting the left channel signal for one half cycle of 38KHz
then the right channel signal for the other half of a 38KHz cycle.

Take the baseband output from the FM discriminator (the stereo audio signal
as transmitted) and feed it to a switch going at 38KHz, and the two outputs
created are the original left and right channel signals. That's the stereo decoder.

If you just listen to the baseband output from the FM discriminator, the two signals blend to create a good monophonic audio signal.

The PLL comes into it because you need the 38KHz switching signal to be
EXACTLY the correct frequency and phase to work.

That's why 10% of the stereo signal from the discriminator is given over to a continuous 19KHz sinewave (sometimes called the pilot tone).

you lock your PLL to the 19KHz tone, and double the frequency to create the
switching signal that you need to seperate the left and right channels.
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