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 Post subject: Unusual tuning presets
PostPosted: Sep Mon 13, 2021 2:44 am 
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Joined: Jan Mon 24, 2011 7:21 am
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Location: saint clair shores, michigan
I grabbed this Craig FM 8 track at a flea market for a couple of bucks. There are three separate tuning indicators and three separate tuning knobs. The indicators and the knobs are identified with a circle and a square and a triangle so you know which knob manipulates which indicator. All three indicators can tune in to any station along the entire FM frequency range. Only the knob that is pushed in will receive the station it is tuned to. So after all three indicators are tuned in to separate stations, you can choose which station you want to listen to by pushing the appropriate tuning knob in. I am curious to take the cover off to see how this system works. I am surmising that there will be three separate tuning capacitors. Has anyone ever seen a similar system?


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 Post subject: Re: Unusual tuning presets
PostPosted: Sep Mon 13, 2021 3:13 am 
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Joined: Jan Fri 06, 2012 8:47 pm
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1968rt wrote:
I grabbed this Craig FM 8 track at a flea market for a couple of bucks. There are three separate tuning indicators and three separate tuning knobs. The indicators and the knobs are identified with a circle and a square and a triangle so you know which knob manipulates which indicator. All three indicators can tune in to any station along the entire FM frequency range. Only the knob that is pushed in will receive the station it is tuned to. So after all three indicators are tuned in to separate stations, you can choose which station you want to listen to by pushing the appropriate tuning knob in. I am curious to take the cover off to see how this system works. I am surmising that there will be three separate tuning capacitors. Has anyone ever seen a similar system?
I get the distinct impression, correct me if I am wrong, that the indicator is not mechanical but LCD or something like that.

As a result I will suggest that the indicator are set up kind of like a voltmeter bar-graph. If that is the case it is entirely possible that the tuning knobs are simply connected to 10 turn pots that are running varactor diodes to do the tuning. I have a 4 channel scanner that did exactly that. there were 4 separate knobs that would tune 4 different varactor diodes and the scanner would then selectively enable the one to be used or you could select it manually.

There literally is NO mechanical tuning capacitor. In this case the indicator is only reading the control voltage to the varactor diodes.

In a strange way it is not all that unlike the old console radio push-buttons that all had their own oscillator coil that were separately tuned to stations.

Just my opinion.

Curtis Eickerman

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 Post subject: Re: Unusual tuning presets
PostPosted: Sep Mon 13, 2021 3:27 am 
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Joined: Jan Mon 24, 2011 7:21 am
Posts: 1036
Location: saint clair shores, michigan
After taking the top off here are the guts. The front is at the bottom of the picture. Now I am thinking the tuning is done in a similar way that vintage car a.m. pushbutton radios worked, Using ferrite bars


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 Post subject: Re: Unusual tuning presets
PostPosted: Sep Thu 16, 2021 2:23 am 
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Joined: Jun Sun 15, 2014 5:37 pm
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Location: Montreal, Quebec
Ablut a week ago, someone posted in the transistor section about an early seventies portable radio that had three presets.

I assume this radio is like that. A trimpot to set the frequency, the variable capacitor of a normal radio replaced by varactor diodes, voltage variable capacitors. A simple pot controls the voltage to them, and hence the frequency.

Mid seventies tv sets did this. A bank of pushbuttons, eniugh for any lication. And behind a panel, a trimpot and switch for each. You set the switch to vhf-lo/vhf-hi/uhf and tune the station with the trimpot. So you set one toeach of the local tv stations, and then easily flip channels. No need to clunk through all the channels. A bit later, it was done digitally.I


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