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

To: amps@contesting.com
Subject: [Amps] More on using a PIC processor inside HF amp
From: Hugh Duff <hughd@cogeco.ca>
Date: Wed, 06 Feb 2008 13:31:29 -0500
List-post: <mailto:amps@contesting.com>
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


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