Huff & Puff overview
If your Huff & Puff doesn't stabilise your VFO immediately on switch-on, or if it ever needs to be reset - then replace it with a fast Huff and Puff. It is very simple to modify an existing 'old' type H&P to the fast configuration. You just have to add a shift register, an XOR gate, and increase the clock frequency.
Fast Huff & Puff simulator program
How does the Fast Huff and Puff stabiliser work?
The Fast Huff & Puff uses a simple principle.
The initial and final Least Significant Bits of an asynchronous count are compared. If they 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.
The VFO is 'corrected' accordingly.
Note that ALL Huff and Puff stabilisers work by comparing the start and final bit of a count.
Explanations involving only the final bit are not correct.
A huff and puff that simply decides to go up when the end bit is high and down when the end bit is low can only produce
a very weak lock, if indeed it produces any lock at all.
The following 'thought experiment' may help you to understand the principle of operation of the (Fast) Huff & Puff -
The first design for the so-called Huff & Puff stabiliser was published in 1973 by the late Klaas Spaargaren, PA0KSB. This was what I call a 'crystal clock' or 'type 1' stabiliser.
In 1996 Klaas published his VFO derived clock (type 2') version. The type 2 has a considerably stronger lock at VFO frequencies below about 40MHz, though it suffers from the disadvantage that the step height is not independent of VFO frequency.
The third main development was in 1998 when QEX magazine published my 'Fast Huff & Puff' stabiliser design (thanks to Klaas and to Pat Hawker, who first published the circuit and an outline of its operation in 'Technical Topics', for their encouragement).
The 'Fast' design was derived from a close analysis of Klaas' earlier models and with the help of computer simulation.
The Fast Huff & Puff stabiliser uses a shift register as a memory and an XOR device as a decision maker.
The 'fast' architecture can be applied to either type of stabiliser and improves lock strength by many times.
Download Fast Huff & Puff simulator program (1.5Mb)
Set your own parameters and watch a simulation of the fast Huff & Puff in action
Notes:
De-install any previous version before starting install.
If you're running VISTA then do not install to 'Program Files' - choose some other folder when give the option on the install screen.
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.
Imagine hopping along a pavement made from alternate black and white blocks.
If your hop is exactly one block long, you will always land on the same colour block as the one from which you started.
If your hop is exactly 1.5 blocks long, you will always end on a different colour block from the one from which you started.
If you increased slightly the length of your next hop when you landed on the same colour as the one you have just left - and
decreased slightly the length of your next hop when you landed on the different colour from the one you have just left, then
the length of your step would hover about a length of one and a quarter blocks.
The following little program is an additional aid to understanding this idea.
Download Fast Huff & Puff visual aid (1.5Mb)