Allison, & others...
Since the time constant in an H&P (Huff and Puff) stabilizer is usually much
longer than that of a traditional PLL, a PIC-based H&P design might be quite
easy to implement. I wonder about the posibility of using the PIC H&P as a
slow tuning PLL-like unit where the PIC would control frequency over the full
tuning range. With such a design the operator might enter a frequency via
the keypad and the PIC would take over and slowly tune the VFO to the
requested frequency. "Slow" here being a relative term that could be quite
fast if a lookup table were employed for gross settings of the DC offset for
particular frequencies.
One big advantage of using a PIC for frequency display is that VFO offsets are
easy to accomodate (i.e. the display can show the operating frequency,
although the actual VFO may be on some other frequency as in superheterodyne
designs). This also works for LSB-CW-USB offsets of the BFO frequency.
This use of a PIC (or any other micro-controller) as a H&P control element is
something that might be best discussed in the context of the Huff & Puff VFO
forum at <>.
Arv K7HKL
_._
toggle quoted message
Show quoted text
On Tuesday 19 July 2005 06:51 am, ajparent1 wrote:
--- In BITX20@..., Jim Strohm <jstrohm@e...> wrote:
> On Jul 10, 2005, at 7:04 AM, Ashhar Farhan wrote:
> > while PLL chips are difficult to find, the 16F84 or the 16F628 are
> > plentiful. why can't we program the PIC to behave as a? PLL on it's?
> > own?
> >
> > the PIC timer can be used to accurately measure the oscillator?
> > frequency
> > (as normal PIC based frequency counters do) instead of displaying the
> > frequency on a display, it can (in addition) also pump a capacitor?
> > that
> > in turn is used to bias a varactor across the VFO.
> >
> > if chris and his merry band can do a single chip HnP, there is no?
> > need to
> > assume that they can't turn out a single mirochip PLL too.
>
> Given how cheap a PIC is, I think it's just a matter of time before?
> we stop using standard TTL/CMOS logic, and start programming PICs as?
> replacements.? They won't be pin-for-pin replacements, but they'll be?
> easier to locate than some of the more esoteric logic chips.
>
> A PIC PLL sounds like a fabulous project.
>
> Jim N6OTQ
Three things:
PIC is a sequential device, there are whole classes of logic solutions
that are not easily done with a sequential device.?
Using the PIC as a PLL, it could be done but even the fastest parts
are far too slow to be succiciently precise.? With PLLs a lack of
precision can be causes noise in the signal.? The core of most PLLs
is the phase detector which is usually a very fast sequential logic
element to in real time compare the phse of two signals.? Hard to do
well enough with a PIC.
Using a PIC for HnP and display, this is very do able.
Allison
KB1GMX
SPONSORED LINKS
Craft hobby
Hobby and craft supply
Ham radio
Hobby supply
Ham radio outlet
Ham radio sales
YAHOO! GROUPS LINKS
?Visit your group "BITX20" on the web.
?
?To unsubscribe from this group, send an email to:
?BITX20-unsubscribe@...
?
?Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
