Re: Follow-up Antuino question
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Farhan
It is possible to reverse the H&P design by dividing the VFO down to LF and letting? it be synched with a very stable HF reference (WWVB or GPS or TCO).? Result is? the same when derived steering voltage is then applied to the HF part of the VFO.
My comments were in response to someone's complaint about Si5351a outputs? being square waves.? With H&P the VFO can be a linear output.??
Arv _._
On Sat, Nov 14, 2020 at 6:39 PM Ashhar Farhan < farhanbox@...> wrote: I was expecting Arv to write in about H&P schemes. Between him and Hans, there is all we know about how this scheme works. The challenge of Huff and Puff is that it needs a very stable oscillator to begin with. It should have very minimal wobble (short term drift). The drift between two correction pulses should be less than its step size. That is not difficult to obtain. The inherent drawback of H&P is that the oscillator is always being pushed up or down from the central frequency between two cycles. This can have a disastrous effect on digital modes. There is probably another way to fix this. It is to use two flip flops as parallel mixers, each is fed the clock pulse that is 90 degrees out of phase from the other (imagine it to be a phasing receiver). Noe, the combined DC output of the two will indicate if we have drifted above, below or stayed on the frequency. I haven't tried this, but I am guessing that this will work. In the professional literature it is called a phase frequency detector. - f
This H&P jitter may not matter much if it isn't very frequent.
If it's a second or two between updates and the frequency slews
at a reasonable rate after an update, the "jitter" should be
no more objectionable than when manually making slight adjustments.
Jerry, KE7ER
On Sat, Nov 14, 2020 at 01:56 PM, Arv Evans wrote:
H&P stabilization is interesting because by default it sets the tuning?
step size as well as holding frequency drift to around 1 Hz, sometimes?
less.? However it does introduce its own type of slow jitter.?
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