VCO

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Analyser
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Re: VCO

Post by Analyser » Mon Jan 08, 2018 7:53 pm

Yes, 3t coild 6mm diameter is about right. The actual output frequency will depend on the capacitance in the tuned circuit but the oscillator may start working with a new coil.
Also, you can try reducing the value of the 1nf capacitor but the PLL lock range will be reduced also. You can increase this again when the VCO starts working.

Also, I just noticed in your copper board picture you have red wire going to ground and black wire supplying the Vcc. Check your supply polarity!

radium98
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Re: VCO

Post by radium98 » Mon Jan 08, 2018 8:14 pm

Analyser last 2 pictures not mines .In my tx forget about polarity because all is good my only problem is the vco not oscillating and i will look for that last thing and report.One question is the schematic of the oscillator ok ? And does it also include first transistor bfw92 ? Thanks

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Re: VCO

Post by Analyser » Mon Jan 08, 2018 8:50 pm

Schematic looks ok to me. Also note the author has built one on the same PCB and it's working.

The BFW92 is just a buffer so the VCO should work wihtout.

Good luck!

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Re: VCO

Post by radium98 » Mon Jan 08, 2018 8:56 pm

Thank you .but author i have tried to contact him many times no luck and i posted my problem.in many forums and the author has built ine but another version mine 1.b i think he 1 or 1.c the one with copper is poster in other forum and the same member posted here long time in this forum too mcruti i think

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Re: VCO

Post by Krakatoa » Tue Jan 09, 2018 6:21 pm

I have been reading... and to me, at least, the design looks ok. It's a Clapp oscillator... there is some info on the web on how it works.
Maybe it does not start oscillating because the transistor is in a wrong DC bias point.
Try the following: unsolder the 27k resistors that go to the base and forget them. Now connect the cursor of a 47k or 50k potentiometer to the base, and the extremes one goes to Gnd and the other to Vcc. Now have ready a frequency counter or a radio tuned to an empty frequency. Power the oscillator circuit and slowly turn the potentiometer each way. At some point the oscillator may start working and generating some random freq. You may also notice its activity by some sound change of the background noise of the radio next to it.
If success, then mesure the two halves of the pot and install the closest fixed values of resistor you find.
Finally, enjoy radio.

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Re: VCO

Post by radium98 » Wed Jan 10, 2018 10:14 am

Krakatoa thank you :) yess maybe it could be i will try last two things the one you told me to that i did before but with 27 k installed and the coil that analyser told me to .very much thank you man .

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Re: VCO

Post by radium98 » Fri Jan 12, 2018 6:33 am

Krakatoa wrote:
Tue Jan 09, 2018 6:21 pm
I have been reading... and to me, at least, the design looks ok. It's a Clapp oscillator... there is some info on the web on how it works.
Maybe it does not start oscillating because the transistor is in a wrong DC bias point.
Try the following: unsolder the 27k resistors that go to the base and forget them. Now connect the cursor of a 47k or 50k potentiometer to the base, and the extremes one goes to Gnd and the other to Vcc. Now have ready a frequency counter or a radio tuned to an empty frequency. Power the oscillator circuit and slowly turn the potentiometer each way. At some point the oscillator may start working and generating some random freq. You may also notice its activity by some sound change of the background noise of the radio next to it.
If success, then mesure the two halves of the pot and install the closest fixed values of resistor you find.
Finally, enjoy radio.
done some more experiments as shown in the picture uploaded paced the probe of a voltmeter or frequencymeter and removing the 2 27k resistors and putting a pot and varying the voltage and listening the a blank frequency on the dial i can listen not to a silent carrier but the some interferencing stations what next and wounding a 3 turns coils .
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Re: VCO

Post by Krakatoa » Fri Jan 12, 2018 9:34 am

If you found your oscillator is now generating some frequency after adjusting the bias pot, then try to measure what frequency is it on, and modify the coil with more or less turns to get it into the fm band.

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Re: VCO

Post by radium98 » Fri Jan 12, 2018 2:48 pm

Krakatoa it is not generating frequency i smell some interferece like i guet on let say 98.2 i can heard a frequency broadcasting on 100.5 ,i dont know if you understand my mean

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Re: VCO

Post by Krakatoa » Fri Jan 12, 2018 5:41 pm

If you are completely sure that the oscillator does nohing at all, then there must be some component that is damaged or out of value. I can't find an explanation to why such simple circuit does not work.
You can rip it apart and adapt another oscillator design.

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Re: VCO

Post by radium98 » Sat Jan 13, 2018 6:59 am

hello again i have adapt another oscillator from another design that it worked but i need the one installed .i dunno can u manage at free time to mekae the oscillator parts on the workbench of you ?

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Re: VCO

Post by Maximus » Sat Jan 13, 2018 9:23 am

I’d check the oscillator coil.


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Re: VCO

Post by radium98 » Sat Jan 13, 2018 2:21 pm

Thank you

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Re: VCO

Post by radium98 » Sat Jan 13, 2018 8:15 pm

I have done a new pcb oscillator parts fitted with bfr91 chinese and it work with printed coil maximum up frequency 81 mhz
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Re: VCO

Post by Albert H » Sun Jan 14, 2018 12:06 pm

Put a solder blob across from the outermost track in the etched coil to the next one in, to reduce the coil by one turn. You should go up in frequency!
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Re: VCO

Post by radium98 » Mon Jan 15, 2018 10:28 am

i will try by today when i gotta home thanks ,one question why the oscillator crash no more on frequencymeter when i tuch the resistor 100k that goes to the varicaps ?

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Re: VCO

Post by radium98 » Mon Jan 15, 2018 8:06 pm

i have reduced the coil by one turn by putting a solder blob from the outermost tracks then the oscillator crash ,then i think i will make 4 turns on a drill of 6mm does it suit for the fm i see someone say 9 turns ?

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Re: VCO

Post by Albert H » Tue Jan 16, 2018 1:55 am

9 turns is much too much. Try 4 turns, then 3 turns - fewer turns, higher frequency. Try 6mm diameter, try 8mm diameter - see what works for you!
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radium98
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Re: VCO

Post by radium98 » Tue Jan 16, 2018 10:18 am

Albert H wrote:
Tue Jan 16, 2018 1:55 am
9 turns is much too much. Try 4 turns, then 3 turns - fewer turns, higher frequency. Try 6mm diameter, try 8mm diameter - see what works for you!
will see , thanks .

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