VCO
- Analyser
- tower block dreamin
- Posts: 319
- Joined: Fri Sep 26, 2014 9:11 pm
Re: VCO
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!
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!
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- proppa neck!
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- Joined: Fri Aug 26, 2016 7:01 pm
Re: VCO
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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- proppa neck!
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Re: VCO
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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- big in da game.. trust
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- Joined: Tue Mar 07, 2017 8:57 pm
Re: VCO
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.
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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- proppa neck!
- Posts: 939
- Joined: Fri Aug 26, 2016 7:01 pm
Re: VCO
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 .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.
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- big in da game.. trust
- Posts: 94
- Joined: Tue Mar 07, 2017 8:57 pm
Re: VCO
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.
You can rip it apart and adapt another oscillator design.