I'm trying to build a test circuit from your schematic to play with but don't understand how it works for changing the frequency!
In my circuit, the frequency is adjusted by changing the voltage on the BB212 varactors in the transistor oscillator's LC tank circuit. This is done via a filtered DUTY-mode output from the Propeller. The output from the oscillator is fed back to the Propeller program which keeps the DUTY mode output adjusted to maintain a frequency and phase lock with its own internal counter, which is set to the same frequency. Because of the low-pass filtering inherent in the software PLL, the counter's jitter is not reflected in the oscillator's output.
I think some people just don't understand the extreme purity requirements of even the simplest radio circuits! If you're looking for all spurious signals say 80dB below the main peak there's no way you can see that on a scope, that's one part in ten-thousand in the voltage domain and probably the same in time/phase domain.
Phase noise of a good oscillator drops to -120dB per Hz or so in a few tens of kHz, that's probably a million times less than would be visible jitter on an oscilloscope screen
The best cheap way to detect phase noise is with a good shortwave receiver that has a BFO. The human ear is way more sensitive to small variations than any eye transfixed by a scope display could ever be.
Hi Phil Pilgrim
So it looks like your design is to basically set the band and default frequency by your spin program!
Are you going to change frequency by an external 10 turn pot say called the "Tuning Control" that basically changes the voltage across the varactors?
Or is it possible that your going to implement more spin software to change the frequency? I'm curious about where the overall design is going here Phil!
The frequency will be set and held by the Propeller. The user will make the selection via an encoder, with the selected frequency visibly incrementing/decrementing on a LCD display.
So then for this project, there's no spin File code listed for the Encoder and no spin code File listed for the LCD for people to do the same as you in this project?
Do you plan on disclosing these spin Files for the project? Thanks!
Comments
In my circuit, the frequency is adjusted by changing the voltage on the BB212 varactors in the transistor oscillator's LC tank circuit. This is done via a filtered DUTY-mode output from the Propeller. The output from the oscillator is fed back to the Propeller program which keeps the DUTY mode output adjusted to maintain a frequency and phase lock with its own internal counter, which is set to the same frequency. Because of the low-pass filtering inherent in the software PLL, the counter's jitter is not reflected in the oscillator's output.
-Phil
-Phil
Phase noise of a good oscillator drops to -120dB per Hz or so in a few tens of kHz, that's probably a million times less than would be visible jitter on an oscilloscope screen
-Phil
So it looks like your design is to basically set the band and default frequency by your spin program!
Are you going to change frequency by an external 10 turn pot say called the "Tuning Control" that basically changes the voltage across the varactors?
Or is it possible that your going to implement more spin software to change the frequency? I'm curious about where the overall design is going here Phil!
Rich W8VK
-Phil
So then for this project, there's no spin File code listed for the Encoder and no spin code File listed for the LCD for people to do the same as you in this project?
Do you plan on disclosing these spin Files for the project? Thanks!
Rich W8VK
-Phil