30-Meter Amateur Radio beacon using Parallax Propeller

Eldon Brown, WA0UWH, has been experimenting with a Parallax Propeller he received for Christmas. Being an avid amateur radio operator, Eldon decided to code up a low power radio beacon on the 30-Meter amateur radio band (10.10 to 10.15 MHz.) He wrote this simple program to generate very slow speed CW (Morse code) radio transmissions (a/k/a QRSS) using the Propeller.

At first he generated the desired signal directly from the Propeller with only the addition of a small attached wire antenna. He went on to modify the design to include a low pass filter (above right) to eliminate the PLL synthesizer phase jitter from the Propeller. He connected a proper outdoor antenna through the filter and is transmitting on 10.1387 MHz.

Check out Eldon’s WA0UWH website for the complete project log.

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  1. Microcontroller counter/timers in NCO mode are very noisy/jittery, this is especially so for output frequencies that are not an integer multiple of the timer’s accumulator. The resultant phase noise would make detecting these signals in small signal work difficult. The transmit filter used in this application will not help with poor close-in phase noise. A very tight crystal filter would be far better, but getting the crystals for a specific non-standard frequency would be difficult and costly. At best this application would be marginally useful as a transmit source but never useful as a decent receive local oscillator.

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