### Crystal Oscillator Design: Parallel and Series

On the Rockmite yahoo group today, Chuck Carpenter, W5USJ posted a very nice explanation of series vs. paralel resonant crystals along with a link to a FAQ on crystal oscillator design at:

http://www.foxonline.com/techfaqs_cry.htm#a4

Chuck' post follows:

RMers,

Here's some info sent to me by Rich at ESS.

Chuck,

The group that requested 7114 requested it in Series Resonant crystal. Most
of the other crystals that I sell are Parallel Resonant. I have included an
explanation from Fox Crystal Co. web site. They are not my supplier but the
information applies to all crystals and their manufacturers. This should
get you where you want to be.

The information that everyone needs to know is #6. 4 and 5 will help people
make a circuit oscillate where they want it.

This is from: http://www.foxonline.com/techfaqs_cry.htm#a4

4. The load capacitance (CL) of my parallel resonant crystal is rated at
20pF. How do I calculate the value of the load capacitors used in my
parallel resonant oscillator circuit?

Use this formula to approximate the value of capacitors needed:

CL=((C1 x C2) / (C1 + C2)) + Cstray

Cstray is the stray capacitance in the circuit, typically 2-5pF. If the
oscillation frequency is high, the capacitor values should be increased to
lower the frequency. If the frequency is low, the capacitor values should be
decreased, thus raising the oscillation frequency. When CL =20pF, C1 and C2
will be approximately 27-33pF each, depending on the amount of stray
capacitance.

Load capacitance is defined as being the total capacitance present in an
oscillator circuit as measured or calculated across the pins of the crystal
socket. Load capacitance has the effect of increasing the frequency of a
crystal unit. Please see the tutorial section for a complete explanation.

6. Will a series crystal work in a parallel circuit and vice versa?

Yes to both, but a crystal unit manufactured as a series resonant crystal
will operate at a frequency higher than expected if used in a parallel
resonant circuit. A crystal unit manufactured as a parallel resonant crystal
will operate at a frequency lower than expected if used in a series resonant
circuit.

If you need any other information then feel free to contact me,

Rich Kennedy - N4ESS
Expanded Spectrum Systems
6645 Founders St.
Zephyrhills, FL. 33542-1828
USA

813-620-0062 Office

www.expandedspectrumsystems.com

n4ess@tampabay.rr.com

Chuck Carpenter, W5USJ, Point, -|- Rains Co., TX -|- EM22cv -|- 72/73
56 years -|- 19 as K2OFN and 37as W5USJ -|- Most fun = QRP since 1984.
Website = http://www.w5usj.com

### Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

### Lost Phone

We were incredibly lucky to have both been in university settings when our kids were born.  When No. 1 arrived, we were both still grad students.  Not long after No. 2 arrived, (about 10 days to be exact), mom-person defended her dissertation and gained the appellation prependage Dr.

While there are lots of perks attendant to grad school, not the least of them phenomenal health insurance, that’s not the one that’s come to mind for me just now.  The one I’m most grateful for at the moment with respect to our kids was the opportunities for sheer independence.  Most days, we’d meet for lunch on the quad of whatever university we were hanging out at at the time, (physics research requires a bit of travel), to eat lunch.  During those lunches, the kids could crawl, toddle, or jog off into the distance.  There were no roads, and therefore no cars.  And, I realize now with a certain wistful bliss I had no knowledge of at the time, there were also very few people at hand that new what a baby…

### Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…