[hpsdr] Gibraltar Prototyping

[Alberto I2PHD]

A couple of years ago I designed and built a GPSDO using the Shera approach, but with a different processor (an Atmel 
AVR AT90S8535) and also different logic components. The OCXO that I used was an Isotemp Mod. OCXO134-12 at 10 MHz. I did 
not use a DAC, but a 20-bit PWM to generate the analog steering voltage for the EFC.
If somebody is interested in the assembler source code for the AVR, it is downloadable from here :
http://sundry.i2phd.com/GPSDO.zip
Except for parts of the LCD display and formatting routines, the code has been written by me, and I put it in the public 
domain, should it be of any good. The parts of the LCD display not written by me are by Murray Greenman ZL1BPU, who 
maybe could be contacted for information.

73  Alberto  I2PHD
---------------------------

Robert McGwier wrote:
> 
> The basic approach is straightforward to describe.
> 
> You use the oscillator you are attempting to steer as the clock for the 
> counter mechanism:  pic,  cpld,  fpga, etc.
> 
> The counter in this mechanism counts the reference.
> 
> If the steerable oscillator frequency is too low,  you will count too 
> many counts of the reference and vice versa if the steerable oscillator 
> frequency is too high.  There is little more to it than that for the 
> error detector.  The fun part is the determination of how many counts of 
> the (too small) counter you need to give you sufficient resolving power 
> on error you are attempting to control and how to keep the system stable 
> without making overly stiff (critical damping), etc.
> 
> I will see what I can find in the way of implementation for someone ELSE 
> to take and do something with.  My plate is full.
> 
> Bob

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