Oscillators for FM radio

[Chiranka K]

I was building a radio receiver for FM waves (87.5-108MHz), I want to build every block on my own (oscillators, mixers, demodulators) and then put them together. I was designing a oscillator, and came across 2 options
1. Colpitts

2. Clapp

I had a few doubts
1. Which of these two performs better?
2. What range of frequency should my LO be able to give?
3. What IF frequency to use (I did my research and most of them show 10.7Mhz).
4. while running a simulation of this on LtSpice, what component should I use for RFC, and what BJT should I use?

Finally, do u think I should be building a receiver for AM or for FM as my first radio receiver?

Thank you.
Chiranka K

 

[danadakk]

1)

Activity: The Clapp Oscillator [Analog Devices Wiki]

wiki.analog.com

Clapp Oscillator: Frequency Formula And Circuit Diagram | Electrical4U

A SIMPLE explanation of Clapp Oscillators. Learn what a Clapp Oscillator is, the frequency formula of a Clapp Oscillator, and a circuit diagram. We also discuss how ...

www.electrical4u.com

Clapp oscillator - Wikipedia

en.wikipedia.org

2) Thats receiver design and band targeted driven selection.

3) 10.7, because of component availability. But if doing LF or HF many receivers use
100Khz or 50 Khz or 455 Khz. Amateur Radio Handbook many discussions on receiver
design.

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org

4) BJT selection, low noise, fT of roughly 10X frequency of interest. Chokes -

https://www.coilcraft.com/getmedia/d4efe41a-82c6-4dbd-97a0-9a24c0a013d4/Coilcraft-eBook_RF_Magnetics.pdf

Regards, Dana.

 

[Chiranka K]

1)

Activity: The Clapp Oscillator [Analog Devices Wiki]

wiki.analog.com

Clapp Oscillator: Frequency Formula And Circuit Diagram | Electrical4U

A SIMPLE explanation of Clapp Oscillators. Learn what a Clapp Oscillator is, the frequency formula of a Clapp Oscillator, and a circuit diagram. We also discuss how ...

www.electrical4u.com

Clapp oscillator - Wikipedia

en.wikipedia.org

2) Thats receiver design and band targeted driven selection.

3) 10.7, because of component availability. But if doing LF or HF many receivers use
100Khz or 50 Khz or 455 Khz. Amateur Radio Handbook many discussions on receiver
design.

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org

4) BJT selection, low noise, fT of roughly 10X frequency of interest. Chokes -

https://www.coilcraft.com/getmedia/d4efe41a-82c6-4dbd-97a0-9a24c0a013d4/Coilcraft-eBook_RF_Magnetics.pdf

Regards, Dana.

Thanks Dana,
Do you think my first radio project should be targeting FM band or AM band?

 

[danadakk]

AM, it gets as simple as :

There is a fair amount of activity by hobbyists in this :

Internet Archive: Digital Library of Free & Borrowable Texts, Movies, Music & Wayback Machine

archive.org

 

[vfone]

Usually Clapp oscillators have better frequency stability than Colpitts oscillators, due to series configuration of the LC resonator.
In the schematic attached if vary C1 between 15pF and 36pF you get a 88MHz to 108MHz signal. C1 could be replaced by a varactor.

 

[danadakk]

Clapp versus Colpitts stability :

Clapp Oscillator : Circuit, Working, Frequency & Its Applications

This Article Discusses an Overview of What is Clapp Oscillator, Circuit, Working, Frequency Advantages and Its Applications

www.elprocus.com

https://www.eecg.utoronto.ca/~kphang/papers/2001/wilkin_vco.pdf Higher loaded Q


Regards, Dana.

 

[Chiranka K]

Usually Clapp oscillators have better frequency stability than Colpitts oscillators, due to series configuration of the LC resonator.
In the schematic attached if vary C1 between 15pF and 36pF you get a 88MHz to 108MHz signal. C1 could be replaced by a varactor.

Is Q2 here used just to get a better gain?

 

[danadakk]

Its to act as a buffer and unload the Clapp LC circuit.

 

[Chiranka K]

Its to act as a buffer and unload the Clapp LC circuit.

and why is the tank (LC series connection) at a different position compared to the other clapp circuits

 

[vfone]

In the Clapp oscillator in #1, the resonator components (Lt and Ct) are also in series.

 

[Chiranka K]

In the Clapp oscillator in #1, the resonator components (Lt and Ct) are also in series.

I did a simulation and got a wave form similar to this, i can tune C7 from 12p to 18p to get my desired freqeuncy range.
However the waves are not pure sine, will it have any problem in mixing stage and on the overall receiver?