[ARC5] Receiver Filter Adaptor Simple ARC 5 xtal receiver?

[Dennis Monticelli]

I will also endorse Bill's commentary along with Frerking's book.

My research involvement includes electro-mechanical resonators among other
things.  We look at different materials (both crystalline and amorphous)
and different 3D shapes and study their modes and characteristics.  The
models that we use are based upon the physics.

I just want to note that the simple electrical models in the books, while
adequate for our purposes, should not be taken too far.  The series L, C,
and R are just analogies for material properties and they only cover the
primary resonant modes of the slab, not the many others that exist in all
mechanical resonators.  For example, it is common practice to talk about
the loss in the crystal in terms of a series resistor.  That loss could be
just as accurately expressed as a parallel loss resistor (of much, much
higher value) and that may be more useful in analyzing certain circuits.
You can calculate this parallel resistor yourself as you would any series
to parallel resonant circuit.  The loss is also not linear.  Shake-n-Bake
that rock with lots of excitation and it changes, not to mention exciting
unwanted secondary resonant modes.

As for using quartz crystals in resonators, there is a reason why these
exist commercially at certain frequency ranges.  Loss and spurious response
matter and the popular cuts perform best at certain frequencies.  For the
cut we are most likely to use, the AT found in most holders from WW2
onward, they don't drop below 100 ohms until 2MHz or greater.  Other cuts
get used at LF.  At >20MHz the third overtone is often used because the
loss then becomes less than the fundamental.  Spurious responses can be
handled via proper oscillator design but in a filter they are harder to
suppress.  Toss in multiple resonators for your filter and it gets
messier.  You can succeed in building a decent oscillator with trial and
error, but a more studied approach is needed with a filter, even a
relatively simple half-lattice.

Better stop now.  Probably TMI :-)

Dennis AE6C

On Thu, Feb 18, 2016 at 8:41 AM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> On 18 Feb 2016 at 18:23, Brian wrote:
>
> >
> > Hello All,
> >
> > I think we should listen to Bill.
>
> I absolutely agree.
>
> > One mistake I suspect the rest of you are making is assuming that if you
> put a
> > capacitor in series with a crystal, that is a series resonant circuit.
> The first
> > thing that most of you are missing is that the series and parallel
> resonances
> > refer to within the crystal, not the circuit outside the crystal.
>
> Yes.
>
> > Go look in any
> > book on crystal oscillators. In the book you may be lucky enough to find
> a chart
> > of frequency versus impedance. If you look at resonant frequencies, you
> will see
> > that the parallel and series resonant frequencies are very close.
>
> I have seen such a graph and, of course, you are correct.
>
> > For instance,
> > see Figure 5.3 on p22 of Marvin Frerking (1978) Crystal oscillator
> design and
> > temperature compensation, Van Nostrand, NY.   Please note email
> etiquette: I
> > have only left attached those emails dealing directly with series and
> parallel
> > crystal resonances.   73 de Brian, VK2GCE. BE, PhD, CPEng, FIEAust  On
>
> Good for you, Brian. I hope your explanation above helps clear the air a
> little.
>
> I have a fairly thick book on crystal manufacturing written by the military
> during and/or after WWII, which goes very heavily into crystal theory.
>
> Bill's explanations most certainly agree with everything I have read in
> that
> pub.
>
> Although I most certainly no expert in these (or most other) matters, what
> I
> have read here during this discussion contained very many misconceptions.
>
> Bill's information was obviously accurate.
>
> Ken W7EKB
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