Another FM receiver with a synchronous oscillator can be found here at http://zpostbox.ru/prostoi_sinkhronnyi_fm_priemnik_na_tranzistorakh.html

It uses the same topology as the Noisy Regen, but is equipped with an RF preamplifier and an emitter follower buffer stage which is directly behind the synchronous oscillator (SO).

The RF preamp stage gives a better sensitivity and isolates the aerial from the synchronous oscillator. The emitter follower buffer stage prevents excessive loading of the SO by the following audio stages.

Alan,

I know this is an old post but was reading it and cannot for the life of me (or with the all mighty power of Google) figure out what you meant by "blurt" tested OK. What is "blurt" tested?

Could you shed some light on this for me?

Thanks!

-- Newell

I am wondering what kind of audio quality

have have schematic:

http://www.uploadarchief.net/files/download/fm-synchroontuner%281%29.gif

Detection isn't done by slope detection, but by synchronising the oscillator frequency to the frequency swing of the incoming FM RF signal. The oscilator frequency follows the frequency swing of the incoming RF signal, the result is that the LF signal is detected by curent changes of the oscilator stage

I have built an FM regenerative receiver with an RF preamp stage, oscillator with the same topology like the noisy regen. The oscillator is synchronised to the incoming signal. Detection is done by slope detection. The results are much better than with an FM regenerative receiver without any RF preamp stage.

Schematic:

http://www.uploadarchief.net/files/download/fm-synchroontuner%281%29.gif

Norman,

Done. Give it a go mate, it is a very simple receiver you should be able to make it very small.

Regards,

Alan

Alan,

I would greatly appreciate your comments or input on a post I put at:

http://www.theradioboard.com/rb/viewtopic.php?t=3445

about the Euro Set. Thanks in advance!!!!

Norman

KA1GUK

Alan,

I had tried using 2SC1815 as the detecting stage but it did not work, probably because of its low ft (around 100 MHz).

I am quite surprised that your receiver doesn't need an antenna. With mine, no sound could be heard if there was no antenna.

Though this little receiver may not produce sound with quality matching commercial products, I am very satisfied with its performance given its simplicity. And I forgot to mention about its smooth feedback adjustment in the last post.

It is difficult to strike a balance between performance and circuit simplicity, but this receiver should be a very good attempt. I hear that pulse counting design, although more complicated than a regen, can perform much better. I probably will give it a try very soon.

Regards,

Ben

Ben,

I'm glad you had success building this receiver.

Yes it isn't exactly "hi-fi" quality. The slope detection has a lot to do with this, but the audio amplifiers aren't low-distortion either.

You could try substituting a "good" AF amplifier of similar input gain and do A/B comparisons to get an idea of how much comes from the AF amp and how much is inherent with the slope detection. To my ears it doesn't sound much different through a better amp, except intermod on audio peaks which is rather bad with the current simplistic amplifier. I now have the capability to measure distortion in a more scientific way, so it would be interesting to study it more closely.

It is a fun receiver though, I really enjoy mine with all its faults. I should rebuild it in a better arrangement.

Mine works "OK" without an antenna around town, but not so well in fringe areas. I've thought about adding a buffered front-end BPF, maybe using the headphone leads as the antenna. If I rebuild it I will likely do this and shield the entire device in a small metal tin.

I'm not completely sure why many of the devices I tried for the detector didn't oscillate. It shouldn't require excessively good Ft transistors. Did you try it will the humble 2SC1815 for the detector?

Regards,

Alan

I just built a similar circuit on a breadboard tonight. The first transistor was changed to 2SC1215 and the others to 2SC1815. Also I cut one of the intermediate AF stage. Of course, as what you mentioned, I adjusted the tuning tank to suit my practice.

When I connected the circuit to a battery, it worked at once. The result was surprisingly good and worth the mark as an excellent performer: high volume, good selectivity and reasonable sound quality.

I noted some points:

1. An antenna is needed. What I did was connecting a short wire via a 5 pF capacitor to a tap in the tuning coil.

2. 2SC1730 also functions normally as the first stage.

3. Although the sound quality is much better than my previous attempts on some superregenerative designs, I am quite aware of the presence of distortion regardless of the sound volume. Could the distortion be caused by slope detection and thus inherent to this design?