How does the Fast Huff and Puff stabiliser work?

The Fast-mode Huff & Puff is quite simple, actually simpler to construct than previous versions!
There are two modifications:

Mod 1) The count is asynchronous with no "dead" period. It is always counting

This is good since dead time is wasted time, time when we are not keeping a watch on the vfo.
However, it means that the count can start at any value even if the input frequency has not changed.
Because of this we can't use just the last bit of the count as an indicator of the input frequency change.
Instead, we use an XOR gate to compare the initial and final states of the count.
If the initial and final states are the same, the probability is that the vfo period is too short. If they are different,
the probability is that the vfo period is too long (or vice-versa, it doesn't matter).
The vfo is corrected accordingly in the usual way (integrator, varicap etc.).

Mod 2) In the fast-mode H&P we use a much greater clock frequency.

This is good because it gives a much closer watch on the vfo, allows much earlier correction of its wanderings,
and we can kick it harder to get it back on track with less fear of knocking it out into the frequency wilderness.
To keep the time duration of the count the same in spite of the higher clock rate we store the start bit of each count in a
delay line (realised by shift register or other memory of some sort). This bit will become available (at the shift register output) for comparison with the last bit of the count after the appropriate time. E.g. for an 8Hz resolution the count must last for 1/8th second (when using the crystal clock type).
Many counts are in process at the same time, a new one starting and a "fully ripened" one ending on each tick of the clock.

DOWNLOADS
If any of these downloads don't install or don't work then please let me know. Hit "E-Mail enquiries' above and send me a mail.
Any other comments welcome.

1) Fast Huff & Puff simulator program
Download Fast Huff & Puff simulator program (1.5Mb)

Set your own parameters and watch a simulation of the fast Huff & Puff in action Notes: The program is a tidied-up version of the software I used to develop the fast H&P. Sorry, no 'Help' file is included as yet. Besides being interesting to watch, the program will tell you the maximum drift a stabiliser with given parameters can handle so you can optimise the stabiliser parameters. This version (13 March 2009) uses better graphics (gdi+) compared to the previous version (gdi), and has some errors corrected Please let me know if the new graphics doesn't work for you! This version can be relied on to get the green lines showing the step boundaries in the right places. It is also better at wider step H&Ps. If you want to use it but already have the previous version installed, then simply install over the previous version. When the install program asks if you wish to abort the install, just click "No" and then when it asks "Are you sure?" click"Yes".