View Full Version : Whats the Propeller and Frequency Synthesizer all about! Can someone Explain?

12-21-2009, 02:16 PM
Hi All!
···· I ran across the Frequency Synthesizer in the Propeller Manual!·Can anyone tell me more about this subject, or lead me to some more reading material? Thanks for reading my post!


12-21-2009, 06:39 PM
Here's a good explanation of the technique:

www.ee.bilkent.edu.tr/~ee411/494973545190600605APP_NOTE_FOX.pdf (http://www.ee.bilkent.edu.tr/~ee411/494973545190600605APP_NOTE_FOX.pdf)


Amateur radio callsign: G1HSM

12-21-2009, 10:31 PM
Yes the propeller can do multiple outputs through something like 128MHz using counters, but the frequency step size varies with the output frequency and there is more jitter (equipollent to phase noise) at certain frequency settings (some multiples of 2^N but can't recall what multiples right now). IMHO the jitter is likely, in any circumstance for the propeller counter RF synthesizer output, to be used for small signal receive work. This is not specific to the propeller, any micro acting in this mode will likely have the same issues.

I have implemented some simple software only DDSs (direct digital synthesizers) in propeller assembler (PASM) via a simple resistive 8-bit R2R digital to analog converter (DAC) with sine (using a look-up table), ramp, triangle, square, but I need to dust them off and post some code here for peer review (long overdue). My DDS's don't use the counters but do have sub Hz tuning and work OK through roughly 100kHz (for the sine case) - and no output anlog filtering. Two cogs running DDSs can ouput quadrature, but I do not thing they will be phase coherent unless I learn how to synchronize PASM cog starts due to hub commutation etc.

A propeller with a cog running a counter for HF output and a cog running a LF DDS when mixed together might make for a workable small signal agile limited-bandwidth transmitter (not receiver L.O.) source, but it is likely you will still need some sort of analog post filtering. The likes of QRSS etc. come to mind.

When posting a question, please be more detailed. Tell us more about what you intend to do. There is an RF synthesizer object for Propeller in the Object Exchange. Take a look...

73's David

12-21-2009, 11:28 PM
Leon and David,
···· Thank you very much for the posts! I will explore and try to learn!· 73's!