FM direct conversion radio

[andreidaniel]

Hi everyone! I found on a book and also on the internet this interesting diagram of a FM direct conversion radio.
The problem is that it was designed for the FM OIRT, not CCIR. As a direct conversion the oscillator works at half of the frequency tunned as is described. Will I be able to adjust the circuits to tune into 88-108?
How many turns should have each coils?
Initially it is said: 3+3 for L1 and 20 for L2 (9 turns in the case of using a small ferrite)

 

[betwixt]

Fig 1. The image isn't available.
Fig 2 & 5. The receiver is super-regenerative so it's AM not FM.
Fig 3. Note that "polar stereo" is not the same as normal pilot tone stereo used almost everywhere.

Brian.

 

[andreidaniel]

I re posted the image. It says that it receive FM band.

 

[vfone]

The super-regenerative receiver can receive FM also:

https://www.youtube.com/watch?v=23NVZA7FhIs

On your schematic, perhaps will be very hard to find the old Russian GT311 "hat" transistors. Have to search the surplus market for some old out-of-use satellites or tanks

https://www.radiomuseum.org/tubes/tube_gt311.html

 

[andreidaniel]

GT311 is not a problem. The same diagram was also posted on a romanian book and the author recommended the BF200 or 214. But also the diagram was designed for OIRT spectrum 65-73MHz. How many turns should I cut?

 

[betwixt]

Superegen receivers can only resolve FM using slope detecton so they are relatively inefficient and do not have the inherent advantage of AM noise reduction a true FM receiver would offer.

Andreidaniel, try removing one turn at a time. It would be very difficult to calculate the exact number of turns you need without knowing all the other circuit parameters. One turn may be enough. As you remove turns it will make the frequency it receives go higher.

Brian.

 

[andreidaniel]

Thank you! I reduced the number of turnes from 9 to 4,25. I tried to tune into stations.. I received some of them but the sound is not so clear as it's written in the book. Also if you want to tune into stations, after selecting one station it is desired to re tune even the input circuit...

Forget this diagram. I will come back to my one fet superreaction receiver. It has a very good sound and the stations don't overlap.

 

[vfone]

Whatever super-regenerative receiver you try (using BJT, FET, Tube) all will have the same sound, whatever modulation you receive, AM, FM, or even SSB. The reason is the concept of the "regeneration" itself.
Edwin Armstrong invented both, the (super)regenerative receiver, and also he invented the superheterodyne receiver.
Superheterodyne receiver allow you to use the right demodulator for a given modulation.
The simplest superheterodyne receiver will work better than any regenerative receiver.

But if you want to try a (super)regenerative type, try to find a schematic that allow tuning the regeneration point, which could be done in different ways.

 

[andreidaniel]

Ok, thank you very much for the information

 

[betwixt]

For super regenerative types, you will get better results with a separate quenching oscillator. It gives more control of the regeneration point which in a single oscillating stage will vary with signal strength and frequency.

Brian.

 

[ledum]

Try google translate for this article
https://translate.google.ru/translate?hl=ru&sl=ru&tl=en&u=http://radiomaster.ru/shemi/fm/pr-b85.php