RSS journey begins..!

[transistor495]

Now I'm in front of 12 components I've bought today for bringing alive "Radio Shack Special" regenerative fm radio. I'm going to test two FET's here BF245C and BF256C and the later one gets preference. I'm sure MPF102 will be overdriven by the trs in my hand

I'm expecting to catch up at least four fm stations hitting me. If anybody have done this project, please input here for some kind of encouragement.

Radio Shack Special

Now I've my general purpose pcb in hand and discussing myself about the component placement and layouts. I don't have time for a designed pcb. Happy holidays!

I don't know y I'm overconfident on the success of this project . I'll post the result within two days. Cheers!

 

[audioguru]

It is a very poor quality AM radio.

To receive an FM station it must be tuned to one side of the station then it "slope detects" the FM by changing it to AM. Then its sensitivity is reduced and it has distortion.
It picks up all kinds of AM interference like static sounds.
If the FM station is in stereo or if it has SCA (restaurant music) then whistles might be heard as interference.
It is overloaded easily by strong local stations so you must fiddle with the sensitivity control while tuning it.
It probably picks up two or more FM stations at the same time.

You found the original copy of the project on a site that copied it long ago. You should have gone to the original site for the updated version:
**broken link removed**

 

[transistor495]

Hey thanks Guruji for ur input!

I'm aware of that it's a slope detector. Let me try it practically it's performance. I'll give u the real results on Sunday.


Ahh..the new version of the circuit making me more encouraged...and the work of this guy also
**broken link removed**

 

[audioguru]

How many strong local FM stations are in your area?
I have about 30 strong ones and about 40 weaker ones. So the poor quality "radio" won't be able to separate them.

 

[transistor495]

These 5 stations are pretty spaced apart I think made it for receiving in my crappy radio

• 101.9 - Ananthapuri FM
• 94.3 - Big FM
• 98.3 - Radio Mirchi
• 95.4 - Club FM
• 92.4 - SFM

4 stereos and I expect whistles...

More are coming as just now only we got FM private operating license.

I found the source coil former is a hard to track item! At last I got a plastic pen body. Wah..it's exactly 8mm dm.

 

[audioguru]

I don't think you can buy a tuning variable capacitor.
Can you buy a cheap FM radio so you can use its tuning variable capacitor?

 

[transistor495]

Actually I bought a 120pf trimmer for this purpose. After making it OK, I will buy a gang cap those available for all in one(AM and FM), one side pins are for AM and other side for FM. Pretty costly.

Humm..otherwise let me make a tuning cap by myself! That website mentions making a homemade variable cap. Didn't u notice that?

 

[audioguru]

A 120pf trimmer capacitor has way too much capacitance for the FM broadcast band.

 

[transistor495]

I've 50pf in stock. That is not at all a problem. First the circuit should come alive. shheeeee sound. That is the trickiest part hehe( I know u know that!)

Umm..around 80 percent over by now. Today itself I'll make first SWITCH ON . Is that ur LM386 produces shee sheee . Let me see.

 

[transistor495]

hooooooooooooooooy!
Switched ON!
Nothing happened with BF256C.
Replaced with 245C. Suddenly shheeeeeeeeeeeeeee.......
It is without any antenna connection.
Now I'm going to make drain coil antenna tap and rest..

The static can be controlled via regen pot. So it's working. But when I touch on the transistor, trimmer etc, the sound goes out.

 

[transistor495]

hahahahaha.........

I replaced the 15p cap before the tuning cap with just a 10p cap. Suddenly what happened...............????

Good music started beating in to my ears...........!! Through speaker!

Even with out any antenna!! How sensitive! This is absolutely true. Believe me!

I can squeeze the coils to adjust different stations!

Now I'm going to make a drain coil tap and connect 6" antenna.

Audioguru where are uu??? Now there's no any whistle on the stereo station right now I'm hearing..

 

[audioguru]

The single transistor FM radio picked up a station? Amazing.
Of course it stops working when you touch its RF parts because the capacitance of your fingers is too high for it.

The sensitivity of a super-regen radio oscillates at an ultrasonic frequency. The stereo sidebands and SCA restaurant music of an FM radio station are also at an ultrasonic frequency. Whistles are produced when the frequencies beat together.

 

[kchriste]

Place a recording of your radio tuned into some Indian music and I'm sure Audioguru will leave a comment! If you tune it off frequency a bit so it sounds like ducks quacking, you'll get a quicker response.
All kidding aside; I can sense your excitement and obviously this is a good learning project for you. Congratulations on your success.

 

[blueroomelectronics]

I can squeeze the coils to adjust different stations!

All I could visualize was it working like a tiny accordion.

Congrats, always exciting to get things working.

 

[transistor495]

Thanks kchriste, thanks BRE.

All I could visualize was it working like a tiny accordion.

LOL..It is exactly like that only.
I need one gang cap!

 

[audioguru]

Radio frequencies for aircraft and air traffic controllers are AM at a frequency that is slightly higher than the FM broadcast band. Your super-regen radio will receive them if an airport is nearby.
When I was a kid I made a crystal radio that picked up communications around an airport.

 

[transistor495]

When I was a kid I made a crystal radio that picked up communications around an airport.

When I am a kid I made a super-regen radio that is going to pick up communications around an airport.

That is really true. This regen receiver is pretty flexible to experiment with.

I've attached a 6" 18SWG wire antenna. I've tuned all the stations available here.

I feel it like a very sensitive little receiver oscillating at a high working frequency.

Not joking! It has picked up stations clearly without any antenna at first. I really wondered where this amazing audio is coming from

With LM386 at full gain mode, it has room-filling audio from my 3" speaker. Normally it sounds almost clear and crisp. Far far better than cheap chinese autoscan little radios.

I'm sure it has more than enough volume for an earphone. Tomorrow I've to find one decent tuning cap and a little experiment for covering the entire band.

Let me tell: It was like a magic when the audio came alive! ..and I'm still excited sitting near the little performer

 

[Nigel Goodwin]

Radio frequencies for aircraft and air traffic controllers are AM at a frequency that is slightly higher than the FM broadcast band. Your super-regen radio will receive them if an airport is nearby.

A super-regen can also wipe out the radio communication to the planes as well - not a good idea!.

 

[audioguru]

Hi Transistor,
Did you need to fiddle with the sensitivity control for each station?
Can the super-regen "radio" mute the reception or cause interference on a nearby FM radio?

 

[transistor495]

No and Yes!


Regen control is fixed. It is pre-adjusted for maximum volume.

That is interesting! I've taken my portable fm radio and tested. It causes about 2 meter limited range of interference(no mute.) around same station and surroundings only. Interference causes the peoples sound like ducks quacking

All I can say is it gives more than we expected from a 1tr fm receiver. I'm really proud of my construction.