Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

FM direct conversion radio

Status
Not open for further replies.

andreidaniel

Member level 2
Joined
Sep 18, 2010
Messages
42
Helped
1
Reputation
5
Reaction score
2
Trophy points
1,288
Location
Romania, Iasi City
Activity points
1,817
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)



fm_receivers_with_pll_2[1].gif
 
Last edited by a moderator:

betwixt

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
14,375
Helped
4,727
Reputation
9,469
Reaction score
4,496
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
122,660
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

Member level 2
Joined
Sep 18, 2010
Messages
42
Helped
1
Reputation
5
Reaction score
2
Trophy points
1,288
Location
Romania, Iasi City
Activity points
1,817
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

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
14,375
Helped
4,727
Reputation
9,469
Reaction score
4,496
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
122,660
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

Member level 2
Joined
Sep 18, 2010
Messages
42
Helped
1
Reputation
5
Reaction score
2
Trophy points
1,288
Location
Romania, Iasi City
Activity points
1,817
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

Advanced Member level 5
Joined
Oct 10, 2001
Messages
5,114
Helped
1,520
Reputation
3,041
Reaction score
1,119
Trophy points
1,393
Activity points
32,351
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.
 

betwixt

Super Moderator
Staff member
Joined
Jul 4, 2009
Messages
14,375
Helped
4,727
Reputation
9,469
Reaction score
4,496
Trophy points
1,393
Location
Aberdyfi, West Wales, UK
Activity points
122,660
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.
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top