Author Topic: Could someone please Help me to make this Into an Colpitts Crystal Transmitter?  (Read 393 times)

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Offline Scarlett133Topic starter

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This is an CW 27,145 MHz Transmitter
 

Offline MathWizard

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Is it just for fun, or as a replacement for something ? Does the circuit work in a simulator ? Have you ever made stuff like this before ?

For something this high frequency, it probably won't work very good on a breadboard. You could always try a lower freq. version, or solder up the circuit on a protoboard or copper clad boar. But you'd probably have to try a few values to get it to work. (IDK maybe it would work right away).

That circuit is missing an audio section. So what is your goal ?
 

Offline fourfathom

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You probably want to put a medium-value resistor from the base of T2 to ground.  T2 is probably supposed to be a class-C amplifier, and without the base resistor the B-E rectification will bias the transistor to the point where is only conducts through an extremely narrow portion of the carrier cycle.  Select the base transistor to give you the desired conduction angle.  I don't know, start with 1K?

Also, that series-resonant output filter (L3, C6) is tuned somewhere around 5 MHz, not 27 MHz.  Even if the values were changed, a single series resonant circuit like that will probably not filter out the harmonics to be ham-legal (-43 dBc, I think).  But that limit only applies to transmitters delivering 5W or more, and you will be lucky to get 100 mW with this design.
We'll search out every place a sick, twisted, solitary misfit might run to! -- I'll start with Radio Shack.
 

Offline Scarlett133Topic starter

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It Works id just Like to Have an Version working with the Crystal from Base to Ground, and the point that it doesnt have an Audio Section is so it just makes an Carrier like in CW :)
 

Offline MathWizard

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Looking up images for 'Colpitts crystal oscillator topologies' and 'common emmiter colpitts crystal oscillator' gets a few, some are common-collector, and then there's common-base, which is nice too. I've made a few crystal Osc, but just for fun, I never tried using them w/ my RF projects yet.


Here's a picture of a couple of circuits, you may have to play with the feedback capacitors, or even the operating point to get it working, and at it's best.
« Last Edit: January 24, 2025, 06:38:35 pm by MathWizard »
 
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Offline Scarlett133Topic starter

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Thank you very much ;D
 


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