[Amps] More on using a PIC processor inside HF amp

[Hugh Duff]

I've been "reading the mail" here on the list and thought it would be worth mentioning another point which comes to mind. If it has already been mentioned then I missed it;

I've been thinking about making my own tube amp control/protection board since the couple of commercially available boards are prohibitively priced. Using a micro would cut out some of the logic parts plus afford me the power to do fancier stuff all at a fraction of the cost. Of course while good shielding and filtering practices to protect the uC from any RF interference and power transients from the amp can also help reduce the leakage of clock frequency harmonics from getting into the system receiver, consideration should also be given to the strategic choice of the uC clocking frequency to minimize RX interference while maintaining maximum performance.

1. Choose a clock frequency for which the harmonics least fall into any of the bands of operation. 

2. Choose the lowest frequency possible i.e. Use the internal LF R/C osc, a LF ceramic resonator or even a 36kHz watch crystal so that the harmonics are well down into the HF spectrum. Chances are the uC is still plenty fast to perform any time critical tasks like shutting down the amp on an overcurrent or voltage condition. Leakage should be low if the micro board is well grounded, shielded and the I/O is filtered using feedthrough caps.

3. If possible choose a clock frequency above the highest frequency of operation. Especially easy for low band monoband amps in the 160m-40m range.  

4. Put the micro into sleep or semi-sleep mode if it's sitting idle most of the time or if something has to be monitored at all times, make use of interrupt inputs that can wake it up when required.

Just a little food for thought...

73 de Hugh VA3TO
http://www.va3to.com