About carrier signal

Thread Starter

PaulEngineer

Joined Dec 21, 2016
163
Hi

I would like to ask you if 500KHz is fine to be carrier frequency. I'm asking that because I have LM565 PLL, and this chip has a VCO output of 500KHz. Can it carry the 20-20KHz?
 

Thread Starter

PaulEngineer

Joined Dec 21, 2016
163
What do you want to do with the modulated signal?
I want to make something like a simple FM radio receiver, by using this LM565. I asked that from someone who tried to help me, (by the way I made a radio receiver using transistors) but he told me that this FM receiver is not working properly on movement, and somehow I need to stabilize the frequency in order to not to lose the frequency. He said me that lm565 is the most suitable for my receiver. That why I ask.
 

MrChips

Joined Oct 2, 2009
20,912
For FM, you need to consider the percentage modulation.
5kHz modulating 500kHz is 1%
5kHz modulating 100MHz is 0.005%
 

LesJones

Joined Jan 8, 2017
2,606
Is your plan to mix down the 100 Mhz receive signal down to around 500 Khz to feed into the LM565. If you do that as a single conversion then the image rejection will will be very poor as the image will only be 1 Mhz away from the desired frequency. You would be better using double conversion with a first IF of 10.7 Mhz (A standard IF frequency.)

Les.
 

Thread Starter

PaulEngineer

Joined Dec 21, 2016
163
Well, I found out what was the problem. I was wrong. Right now, I found a pdf that explains how exactly the lm565 works. So the input of the FM signal was from the pins 2-3, and the output was from pin 7. The 500Khz as I seen has nothing to do with the input of PLL lm565. It was the output reference of VCO to the input of phase detector. Guys I'm really appreciate for your help. So I didn't gave up, and found what was going wrong. I have seen many schematics out there that show the wiring of lm565. I carefully checked every circuit and they were more or less like same idea. The input was FM, all the time. And I thought, if lm565 has input 500KHz, why 100MHz of FM is on the input. So I found out what was going on. This pdf clearly explained me how is all working.
 

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