Technical Topics > The RF Workbench
Stretchyman 40 W TX Reliability Modifications
Stretchyman:
https://www.analog.com/media/en/technical-documentation/application-notes/an-423.pdf
Yes, we've known about this for sometime!
25 years!
However generating low power A M. and using a linear isn't very efficient. Plenty of folk still using that method as they don't know any better!
Class E is the way to go, Simple, Efficient, Perfect!
+ DDS's are generally used to generate frequencies these days and are a single chip and as simple to program as an Arduino. Complex synths and PLLs are no longer nessarary.
No point searching the web for any decent designs as all you generally find is a load of old rubbish designs from 30+ years ago.
Modern design are usually confined to datasheets from the manufacturer or others in the know...
Str.
Charlie_Dont_Surf:
--- Quote from: Dare4444 on January 22, 2022, 1934 UTC --- No crystals or complex synthesizer needed. A simple Arduino code sets the TX frequency!!
--- End quote ---
No disrespect to you personally intended but I consider myself to be comfortable enough with microcontrollers and synthesizers to be "dangerous" with them and I don't feel this to be a terribly simple solution. You need a microcontroller, you have had to write software for it, then the output is pretty weak and it will need a decent linear amplifier (which you have not discussed here) to boost the output to be heard farther than 10 meters away. Also, I don't consider the AD9850 to be a particularly simple synthesizer. Perhaps it appears that way if you treat it like a black box and don't know what's going on inside but I don't recommend doing that. (I actually don't feel that any synthesizer is "simple".)
To be clear, there is a need and a place for synthesizers and I don't know how you do a AD9850 (and the like)-based synth without something providing the digital words to them (here, it's a microcontroller) but let's not pretend that this is a simple solution.
So not my cup of tea, but to each his or her own I suppose.
Finally, I'm not quite sure why this ended up here in this thread. It's completely unrelated to the original topic.
Stretchyman:
Indeed, somewhat off topic.
However once you have the code written it's a no brainer.
I have 64ch code for the AD9850 PCBs that are readily available. The opposing squarewave outputs will drive FET drivers directly. Commonly use for class D/E push pull.
Also have single channel software for the AD9833 (<$2) PCBs and use a discrete 3 tran amp to get to 5V p-p to directly drive FET driver for single ended transmitter.
Saves all that xtal nonsense!
Str.
Charlie_Dont_Surf:
I don't know how many versions of your synths you have gone through but the ones that I have used have always ended up a bit lower in frequency than I would like - usually about ~100 Hertz low. We're not expecting WWV accuracy here and the consequences of this are not the end of the world but I think that we can agree that they could be closer to target.
I suspect that a number of the loggings on this website indicated as "xxxx.9 KHz" (more or less) come from your synths, but I can't prove that. Perhaps this is yet another way to identify one of your transmitters on the air. ;D
ChrisSmolinski:
--- Quote from: Charlie_Dont_Surf on February 21, 2022, 2147 UTC ---I suspect that a number of the loggings on this website indicated as "xxxx.9 KHz" (more or less) come from your synths, but I can't prove that. Perhaps this is yet another way to identify one of your transmitters on the air. ;D
--- End quote ---
There may indeed be a statistical anomaly regarding frequency offsets from integer values in pirate loggings. I will add it to the list of things to investigate ;D
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