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Old 7th Oct 2017, 8:47 pm   #1
Goldieoldie
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Default Auto tuning radio theory of operation

Hi
I have a Hitachi wm 800 radio which has auto tuning
Basically there is a clockwork motor that drives the tuning cap which then stops
When a signal is received .
Although working it struggles because of the amount of interference on am
I have attached a pic of the motor and a circuit
Does anyone have one of these and can explain how the circuit works please ?
It has an if oscillator ?
Cheers Pete
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Old 7th Oct 2017, 8:48 pm   #2
Goldieoldie
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Default Re: Auto tuning radio theory of operation

Clockwork motor !
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Old 7th Oct 2017, 9:02 pm   #3
Andrew2
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Default Re: Auto tuning radio theory of operation

It seems to be a simple matter of D002 rectifying the audio at the output of the audio amplifier and turning on the transistor. The current pulls in the solenoid and stops the motor. Sadly it works on any audio, even noise!
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Old 7th Oct 2017, 9:22 pm   #4
ms660
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Default Re: Auto tuning radio theory of operation

Zero beat (BFO) for station detection then audio amp connects to loudspeaker as well as the detector output once zero beat (or near as damn it) is achieved and relay switches over.

Lawrence.

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Old 7th Oct 2017, 9:58 pm   #5
Goldieoldie
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Default Re: Auto tuning radio theory of operation

Hi Lawrence,
So using a bfo .Does that mean it's a bit more clever than just looking for a am signal ?
I'e, so noise should not trigger it ?
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Old 7th Oct 2017, 10:01 pm   #6
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Default Re: Auto tuning radio theory of operation

Quote:
Originally Posted by ms660 View Post
Zero beat (BFO) for station detection then audio amp connects to loudspeaker as well as the detector output once zero beat (or near as damn it) is achieved and relay switches over.
Yes I agree with that interpretation, it also looks like the tuning is spring wound so the auto would only start searching from one end on the dial.

It seems a very complicated system for a small portable radio.

Edit. A noise pulse would probably not trigger it, there will be some longer time constant to protect against that but a carrier from a SMPS would be treated as a signal like a standard carrier from a broadcast.
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Old 7th Oct 2017, 10:23 pm   #7
julie_m
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Default Re: Auto tuning radio theory of operation

TR002 turns on the relay via (R94?) the (8.2kΩ?) resistor, and also sets the clockwork drive in motion. D002 turns TR002 off on strong positive-going peaks of the signal being fed to the loudspeaker. In the presence of sufficient low-frequency contact, the relay does not have time to re-engage between successive "turn-offs".

A self-tuning pocket radio must have looked like a unique selling point at the time, but the buying public ultimately rejected it as just another gimmick.
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Old 7th Oct 2017, 10:49 pm   #8
Goldieoldie
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Default Re: Auto tuning radio theory of operation

In practice ( after you have wound it up ! ) you press the top button which sets the thing off with the relay pulled in .On finding a signal the relay pops off and there is your station
It's quite clever mechanically as when it reaches the end of the dial it auto reverses !
It's the sort of thing Philips would invent ( over complicated ! ) but for a major Japanese company to do is a bit strange .Maybe the design team had had a good lunch !
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Old 8th Oct 2017, 12:27 am   #9
emeritus
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Default Re: Auto tuning radio theory of operation

When I was a vacation student at Plessey West Leigh in 1967, one of the engineers who was staying in the same digs, had a clockwork autotuning, autoreversing, AM/FM radio like that which he had bought some time previously during a trip to the USA. It would scan up, down, and up again on one wind. From memory, it did look like the picture in the corner of the circuit diagram. Until this post have never come across any references to this type of clockwork radio (not that I have looked for any).

When I was at Plessey Ilford in the early 1970's another engineer brought in a clockwork-tuned FM-only radio he had bought in Singapore that was a similar shape to, but about half as big again as, a disposable cigarette lighter. This had no winder, the clockwork mechanism being operated by pushing in and releasing a button that stuck out at the end with your thumb each time you wanted to step to the next station. I can't remember if it had a speaker or if you had to use the earpiece. I think it may have been a Sony.

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Old 8th Oct 2017, 6:48 am   #10
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Default Re: Auto tuning radio theory of operation

I have a Blaupunkt _valved_ car radio with a mechanism like that. There is a solenoid to shift the pointer to the start end and wind the mechanism, then it seeks along the band until the AGC signal is strong enough (I think) and stops. Hitting a button gets it to seek to the next station on the band.

Said set is MW/LW/FM, the control unit (everything but the vibrator power supply and audio output stage) is not much larger than a modern car radio).
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Old 10th Oct 2017, 4:22 pm   #11
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Default Re: Auto tuning radio theory of operation

Quote:
Originally Posted by emeritus View Post
When I was a vacation student at Plessey West Leigh in 1967, one of the engineers who was staying in the same digs, had a clockwork autotuning, autoreversing, AM/FM radio like that which he had bought some time previously during a trip to the USA. It would scan up, down, and up again on one wind. From memory, it did look like the picture in the corner of the circuit diagram. Until this post have never come across any references to this type of clockwork radio (not that I have looked for any).

When I was at Plessey Ilford in the early 1970's another engineer brought in a clockwork-tuned FM-only radio he had bought in Singapore that was a similar shape to, but about half as big again as, a disposable cigarette lighter. This had no winder, the clockwork mechanism being operated by pushing in and releasing a button that stuck out at the end with your thumb each time you wanted to step to the next station. I can't remember if it had a speaker or if you had to use the earpiece. I think it may have been a Sony.
It possibly a "Panasonic Radarmatic". They used the wind-up clockwork type of motor drive. They made them both in AM only and AM-FM versions.
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Old 11th Oct 2017, 9:32 am   #12
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Default Re: Auto tuning radio theory of operation

I used to work for Wandel & Goltermann, a high-end German telecomms test equipment company. They briefly got into car radios at one point, and also had a clockwork-powered car radio. As this had a car battery behind it, it could also rewind the clockwork automatically. As with all things W&G, it was Rolls-Royce quality, and way too expensive!
Fun to play with on a visit to their museum when I was in Germany training!
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