Cannot change 90 Mhz FM receiver (SRR) to 16 MHz FM

Thread Starter

kabirh56

Joined Oct 2, 2023
20
Dear Experts,
After some trial and errors, I am able to get FM reception in this Super regenerative receiver circuit at 90-110 MHz range.
The system has basic components at 9 v battery input.
Now when i am trying to change the LC tank so it matches 16 Mhz frequency, The Super regen quenching sound is not there anymore. It seems that the circuit is tuned in some other way to respond to around 90 MHz only.
I have tried the LT spice analysis but I could not understand how can I get the regen Output.
So:
1. Could someone help me on what to modify, so that the SRR circuit works in the 16Mhz range?
2. Can anyone tell me how to see the regen output in the FIle provided?

At the end of the day I need to make a 16 MHz FM type receiver with minimum components which are generally available....
Please write as much information as you can. I wont mind .
 

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Thread Starter

kabirh56

Joined Oct 2, 2023
20
No Sir. It is hobby work but I have been trying to get it right for some lengthy time. Electronics is my hobby and FM is new to me. There are many wrong circuits over the internet that adds up to frustration. I suspect I did some silly mistake which can be corrected by experts.
 

Audioguru again

Joined Oct 21, 2019
6,696
A real FM receiver uses an FM detector that ignors the amplitude click and pop interferences that are heard on AM radios.
A super regen radio uses an AM detector that demodulates the amplifude variations of an FM transmission when it it is tuned to one side of the station's frequency.
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
If you only tried to change L2 & C8, I would expect at least C3, L1 and possibly C7 to need changing.
Yes sir. I did that. You are right..I also had to change the resistor bias and I can see quench but have not made the physical circuit yet...
.......
I want to find more information on this and other interesting similar projects .does anyone know of simple , verified fm/walkie talkie/ website names that I can find in google?? Will be glad to learn. There are many websites who show absolutely wrong circuits...but websites of good knowledgeable people are truly gems..let me know if anyone knows.tc
 

seanstevens

Joined Sep 22, 2009
253
Super regenerative receivers are not very stable, sensitive and lacking in quality as pointed out by Audioguru especially if you want to make a walkie talkie with a reasonable range. You either need to use some dedicated chips or build a complex circuit yourself.
However, a simple search on Google brings up:
Simple walkies including ones using nRF24L01
A very simple one that I made 50 years ago seems to be still alive:
Simple walkie

A word of warning, BE AWARE OF LOCAL LAWS or you may get into trouble.
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
Super regenerative receivers are not very stable, sensitive and lacking in quality as pointed out by Audioguru especially if you want to make a walkie talkie with a reasonable range. You either need to use some dedicated chips or build a complex circuit yourself.
However, a simple search on Google brings up:
Simple walkies including ones using nRF24L01
A very simple one that I made 50 years ago seems to be still alive:
Simple walkie

A word of warning, BE AWARE OF LOCAL LAWS or you may get into trouble.
Thank you Sean, for a detail description and sharing the link. I saw this kind of walkie talkie circuit before, thought that it was a false one because the speaker itself is used as mic... but i will check the receiver as you made it before.

BTW. Update: I made the regen work at HF and it did not catch the intended station but some other station, looks like the final frequency shifted to around 8-10 MHz even though the tank circuit was tuned to 16 Mhz.. I did not understand why. Will check tomorrow may be.
Thanks for your suggestions guys. If some new suggestions come up, let me kno.
 
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Thread Starter

kabirh56

Joined Oct 2, 2023
20
A real FM receiver uses an FM detector that ignors the amplitude click and pop interferences that are heard on AM radios.
A super regen radio uses an AM detector that demodulates the amplifude variations of an FM transmission when it it is tuned to one side of the station's frequency.
Yes I understand you Audioguru,
I thought that also. But I have not used any FM demodulationg ICs in project.. But trying with some 2n3904s I already have. I am looking for transistor run receivers actually. Not readymade ICs/ PLL like that. Wonder what kind of circuit will be most stable yet Simple.
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
Super regenerative receivers are not very stable, sensitive and lacking in quality as pointed out by Audioguru especially if you want to make a walkie talkie with a reasonable range. You either need to use some dedicated chips or build a complex circuit yourself.
However, a simple search on Google brings up:
Simple walkies including ones using nRF24L01
A very simple one that I made 50 years ago seems to be still alive:
Simple walkie

A word of warning, BE AWARE OF LOCAL LAWS or you may get into trouble.
Also about the circuit for walkie talkie: it does not have any active connection with the speaker/ microphone when T switches are on. So the circuit will not work. Do you remember usig a different circuit?
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
Also about the circuit for walkie talkie: it does not have any active connection with the speaker/ microphone when T switches are on. So the circuit will not work. Do you remember usig a different circuit?
Sorry i was wrong about the circuit. it is actually connected via the amp. The circuit can work i believe.
 

seanstevens

Joined Sep 22, 2009
253
The one I made, used the speaker as a microphone in transmit mode, switched via a multi-contact push-to-talk button.

BTW. Update: I made the regen work at HF and it did not catch the intended station but some other station, looks like the final frequency shifted to around 8-10 MHz even though the tank circuit was tuned to 16 Mhz.. I did not understand why. Will check tomorrow may be.
Thanks for your suggestions guys. If some new suggestions come up, let me kn
As I said they are not very stable, it depends on your construction. RF techniques need to be used, i.e. short leads and lots of ground plane. Good luck.
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
I have attached the super regen receiver files below. The frequency output is near 16MHz. I can get quench when amp and antenna is not connected . But once connected it goes away. Does anyone have any idea what is wrong? Please feel free to ask any further question in detail
 

Attachments

Danko

Joined Nov 22, 2017
1,835
Hi Mr. Danko,
Sorry, I am not asking about this thread. I could not contact you personally so I am posting here...Hope you will not mind.
I have recently posted one question: "I cannot change a 90 MHZ superregen receiver to 16 MHz." I achieved quenching successfully but now when I connect the amp stage, the quenching stops. Could you help kindly. Can you tell me which things are wrong like you described earlier in forum?
Please check my recent post in my profile. Thank you
The frequency output is near 16MHz. I can get quench when amp and antenna is not connected . But once connected it goes away.
Try to decrease capacitor between amp and detector by up to few pF.
ADDED:
If you mean not RF, but audio amp, try to use amp with higher input resistance.
Decrease input RF FM signal.

Again extremely sorry to ask in different thread, I asked because I could find experienced people speaking here.
People who want to share advise, kindly do .. The question is about making modifications in a FM receiver circuit to change frequency from 90 MHz to 16 MHz.. shown below. Or please visit my profile and check latest post. Thanks in advance.
You can use AM detector, like in this circuit:
http://www.electroniq.net/radio-frequency/am-regenerative-receiver.html
It should receive FM too.
1696686677275.png
 
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Thread Starter

kabirh56

Joined Oct 2, 2023
20
Try to decrease capacitor between amp and detector up to few pF.



You can use AM detector, like in this circuit:
http://www.electroniq.net/radio-frequency/am-regenerative-receiver.html
It should receive FM too.
View attachment 304394
Thank you sir. My circuit responded well to your advice. I will also try your AM detector concept. I did not know that it can receive FM too as I am really new. Thank you a lot.. God blessed you with knowledge and pin point answering ability. Let me know if you have any Blog/ Channels I can follow.I am from different field, new in electronics learning.
 

MisterBill2

Joined Jan 23, 2018
18,538
If it stops oscillating when the antenna is connected that points toward inadequate feedback. That would possibly be due to the effect of C3 shunting too much signal to the common. so if you put a small RF choke between the collector and the junction of C3 and C4 that should allow more feedback while still allowing the audio to pass thru.
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
If it stops oscillating when the antenna is connected that points toward inadequate feedback. That would possibly be due to the effect of C3 shunting too much signal to the common. so if you put a small RF choke between the collector and the junction of C3 and C4 that should allow more feedback while still allowing the audio to pass thru.
Thank you for your advice sir.
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
Try to decrease capacitor between amp and detector by up to few pF.
Dear Sir,
Wish you a good morning. I checked the new FM/AM receiver, it did not quench as expected. also the operating frequency is too low than 16 MHz. It is not going up to 16MHz. going to 8 Mhz with very low gain. I am back to modifying the old circuit.
Circuit is attached.

If you ever find a working/Tested version of FM receiver in around 16-25-32 MHz range, with possible power of 9 volt kindly share the link. There are many circuits online which did not work.

ON a side note:
I realised the signal should be a current input not Voltage. As a Sinusoidal Voltage source will try to pin the connection to ground. I am giving the circuit a try with these changes. But I feel blind with little knowledge in this domain. How the quench depends on Capacitor/inductor/resistance in the circuit would have been really helpful. (I just know the working freq=1/2.pi.root(LC), Quench freq= 1/0.5.R.C, DC Biasing by Resistor, AC biasing by capacitor. Rest is trial and error which I dont like. Wish i knew where to get the required knowledge)
 

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MisterBill2

Joined Jan 23, 2018
18,538
A much more complex, but better performing FM receiver is found inside one IC, the CA3089. That is presented as an amplifier/limiter/detector device now available from multiple sources. It will need some RF amplification between it and he antenna, but stable fixed frequency amplifiers are a very mature technology. So that may be worth a bit of investigation.
One question: What sort of FM signals are you hoping to intercept in the 16mHz realm? My impression was that is where security fobs operate.
 

Thread Starter

kabirh56

Joined Oct 2, 2023
20
A much more complex, but better performing FM receiver is found inside one IC, the CA3089. That is presented as an amplifier/limiter/detector device now available from multiple sources. It will need some RF amplification between it and he antenna, but stable fixed frequency amplifiers are a very mature technology. So that may be worth a bit of investigation.
One question: What sort of FM signals are you hoping to intercept in the 16mHz realm? My impression was that is where security fobs operate.
I was looking for old school transistor technology as fun experiment. not looking for IC or store-bought radio. I think I heard many shortwave stations in that range from 10 to 32 may be. But common FM is limited to 90-108 because the quarter wave antenna length is earphone length. Now I want to see if it can receive well in SW also. It feels good when a radio frequency comes up. Buying a radio is not a choice I want to go for.
Bottom line is, Is there any book/blog where I can get calculations of super regen quenching?

Dont have any idea what Security fobs is. but staying far away from anything "security" is generally good idea I think. Experimenters should be careful as top priority.
 
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