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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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7th Oct 2017, 8:47 pm | #1 |
Octode
Join Date: Jul 2014
Location: Petersfield, Hampshire, UK.
Posts: 1,043
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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 |
7th Oct 2017, 8:48 pm | #2 |
Octode
Join Date: Jul 2014
Location: Petersfield, Hampshire, UK.
Posts: 1,043
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Re: Auto tuning radio theory of operation
Clockwork motor !
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7th Oct 2017, 9:02 pm | #3 |
Nonode
Join Date: Mar 2010
Location: Dukinfield, Cheshire, UK.
Posts: 2,034
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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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Andy G1HBE. |
7th Oct 2017, 9:22 pm | #4 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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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. Last edited by ms660; 7th Oct 2017 at 9:36 pm. Reason: addition/correction |
7th Oct 2017, 9:58 pm | #5 |
Octode
Join Date: Jul 2014
Location: Petersfield, Hampshire, UK.
Posts: 1,043
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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 ? |
7th Oct 2017, 10:01 pm | #6 | |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,427
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Re: Auto tuning radio theory of operation
Quote:
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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Frank Last edited by Nuvistor; 7th Oct 2017 at 10:08 pm. |
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7th Oct 2017, 10:23 pm | #7 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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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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If I have seen further than others, it is because I was standing on a pile of failed experiments. |
7th Oct 2017, 10:49 pm | #8 |
Octode
Join Date: Jul 2014
Location: Petersfield, Hampshire, UK.
Posts: 1,043
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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 ! |
8th Oct 2017, 12:27 am | #9 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
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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. Last edited by emeritus; 8th Oct 2017 at 12:47 am. |
8th Oct 2017, 6:48 am | #10 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
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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). |
10th Oct 2017, 4:22 pm | #11 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: Auto tuning radio theory of operation
Quote:
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11th Oct 2017, 9:32 am | #12 |
Triode
Join Date: Sep 2017
Location: Tavistock, Devon, UK.
Posts: 32
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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! |