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 Post subject: ONE TRANSISTOR FM SUPERHET RECEIVER
PostPosted: Jul Fri 17, 2020 1:21 pm 
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Joined: Feb Sun 16, 2014 10:03 am
Posts: 51
Hi..
yes you read it right..only one HF transistor FM suprehet receiver is here.
Of course you need small audio amplifier with it.
Easy to build and sound very well for such a simple design.
You can build it without ceramic 3 pin 10.7Mhz fileter (u can use 2 pin 10.7Mhz too)
but then selectivity is lower ,but still work for stronger stations.
Also very important part of this receiver is antenna ,made with insulated electric wire 1.5mm dia.
Ideal should be the size of full wave but also is fine with 1/4 lambda size.
In this circuit role of HF transformer play small toroid i picked from old fluorescent lamp electronic (15W).
original idea of that detector comes from one Japan site.
I use well known BFR91A transistor ,but you can try with C3355,BFG65 or with S9018.
good luck !


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 Post subject: Re: ONE TRANSISTOR FM SUPERHET RECEIVER
PostPosted: Jul Wed 22, 2020 10:14 pm 
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Joined: Oct Fri 11, 2019 3:03 am
Posts: 40
Location: Seattle, WA 98122 (from Hungary)
That thing looks like a ratio detector - however the "LC tank" is missing the capacitor, therefore I'm wondering if it's truly working as an FM detector, or just making an illusion that it's detecting FM, but in reality it's just a mistuned AM detector (like in many single transistor super-regen designs).


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 Post subject: Re: ONE TRANSISTOR FM SUPERHET RECEIVER
PostPosted: Jul Wed 22, 2020 10:37 pm 
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Joined: Oct Fri 11, 2019 3:03 am
Posts: 40
Location: Seattle, WA 98122 (from Hungary)
Also, the 1SS93 is a silicon diode, similar to the 1N4148. With that 330 ohm load resistor on the mixer, and through the ceramic filter, I've been wondering how this radio would crank out the 0.6V to open the detector diodes. Maybe there's a 100kW transmitter one block away.


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 Post subject: Re: ONE TRANSISTOR FM SUPERHET RECEIVER
PostPosted: Jul Thu 23, 2020 1:21 am 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 3900
Location: Lexington, KY USA
I won't claim to have any idea if this thing actually works, or how well it might work. I suspect that the circuit seen here is the result of a great deal of tinkering, rather than the product of a draw it, simulate it, build it process.

Clearly, there is no LC tank at the IF. Only the ceramic resonator resonates there. I would think the thing might work better if the transformer had a resonating capacitor.

The 330 ohm resistor is not a load resistor, it is in series with the transformer primary winding. Perhaps it provides some phase shift in the primary current, vs. the voltage at the collector.

Ordinary junction diodes have forward conduction at as low a voltage as you might want. Just not as much. You could go look it up.

Ted


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 Post subject: Re: ONE TRANSISTOR FM SUPERHET RECEIVER
PostPosted: Jul Thu 23, 2020 1:41 am 
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Joined: Apr Thu 09, 2020 7:33 am
Posts: 155
Ingenious better than one transistor super regenerative and not have tuning at left or right sound cleaner because it has a real fm detector and can tune in middle not like slope detector. Very good!!!


Last edited by Chriscrosley1 on Jul Thu 23, 2020 7:13 pm, edited 2 times in total.

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 Post subject: Re: ONE TRANSISTOR FM SUPERHET RECEIVER
PostPosted: Jul Thu 23, 2020 1:52 am 
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Joined: Oct Fri 11, 2019 3:03 am
Posts: 40
Location: Seattle, WA 98122 (from Hungary)
Ok, I just noticed that there is indeed a primary winding of the IF and that's in series with the 330 ohm resistor (kind of have to look at the coil drawing and the numbers to realize).
I take everything back, maybe the ceramic resonator provides the frequency-dependent phase shift necessary for FM detection - in that case that would be the tuned element and there would be no need for a capacitor.
I'm still sceptical on the diodes though; could be just a typo, nevertheless I'd use point contact Ge diodes.


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 Post subject: Re: ONE TRANSISTOR FM SUPERHET RECEIVER
PostPosted: Jul Thu 23, 2020 4:36 pm 
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Joined: Feb Sun 16, 2014 10:03 am
Posts: 51
Hello
I am glad that someone reply to my post .
Yes it is a phase shift transformer built with small toroid from fluo-lamp.
As i already say in my post ,original design of RATIO detector is from one japan site where author explain how to build
ratio detector with toroid and i was sceptical but then i try to combine it with colpits oscillator with traansistor BFR91a
you may try with well known S9018 or with C3355, anyway must be VHF transitor.
as you can see i use standard double tuned variable cap from old FM transistor radio.
best results you can get with antenna on a given image.it work well for me.

For diode you can use AA or germanium if you have it,i have tried whith Ge and then with silicon and result is same.
Circuit work without 10,7 ceramic filter but then selecitivity is not very good.

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