November 17, 2015
CWTD Episode #76
An "Analyze This!"
style discussion of a fabulous resource from Texas Instruments
And updates on:
GPS-DO Project ....
Elmer 101 Course
GPS Display Terminal
With guest designers:
Craig AA0ZZ, Larry K3PEG,
Dave AD7JT and Mike WA8BXN
We found this really well done reference manual called
the "Analog Engineer's Pocket Reference" from Texas Instruments and
we just knew that we had to share it with our CWTD audience! And
what better way to do this than in the style of our long-standing
"Analyze This!" episodes, whereby we go through the relevant sections in a step-by-step manner, providing parenthetical
insight and experience as it relates to all us homebrewers and
Additionally, we've been crankin' with the midnight oil
burning in the background on our THREE MAJOR EFFORTS here in recent
months on CWTD ... The GPS-Disciplined Oscillator project, the
Elmer 101 Course and its companion SW30+ Transceiver Kit.
Here in this episode, our CWTD Dev Team brings us all up to speed with various
aspects of these projects that will soon be breaking upon the shores of
73, George N2APB and Joe N2CX
... Click to play, or right-click to download and archive on your
window comments made during the show ...
<20:03:57> "Alan W2AEW": link:http://www.cwtd.org/Analog_Dialogue/index.html
<20:07:09> "Alan W2AEW": Nice to be here (sitting in a hotel room in
<20:08:41> "Alan W2AEW": If you're really against registering, you
can find it here"
<20:08:59> "Alan W2AEW":
<20:15:52> "Alan W2AEW": If anyone wants a review of the decibel
(dB), as well as dBm, dBc, etc. - with specific spectrum analyzer
examples, you can see my video:
<20:18:19> "George N2APB": Yes, this is a great reference of Alan's.
Love your video "tutorial series on YouTube.
<20:20:10> "Alan W2AEW": Thanks - here is a playlist of four op amp
tutorial videos I did (basics, summing amps, power supply
considerations, peak detectors):
<20:24:25> "Alan W2AEW": (actually 5 videos - also includes gain-BW
<20:25:33> "Mike WA8BXN": we may see something like this in the
<20:29:53> "K2LAZ de Laz": lady ada had the author of art of
electronics and he shared his favorite plot which was a selector
guide for op amps
<20:30:19> "Alan W2AEW": It also gives you a good idea of the
harmonic frequency content of digital signals (all related to
<20:31:10> "Alan W2AEW": Paul Horowitz interview with Lady Ada:
<20:33:17> "Alan W2AEW": Instrumentation amps have very good Common
Mode Rejection (CMRR)
<20:33:46> "K2LAZ de Laz": he went at great length to how to use his
guide: important component is noise level
<20:34:02> "Alan W2AEW": Great for sensing small voltages in the
presence of large common mode noise
<20:38:13> "Alan W2AEW": ...75 ohm cable is generally lower loss
<20:39:24> "K2LAZ de Laz": is 9914 similar to 9913?
<20:39:47> "Dave AA3UR": A low dipole can have an impedance closer
to 75 ohms than 50
<20:43:17> "Alan W2AEW": Here is a video on measuring coax impedance
(and length) using a scope and signal generator:
<20:48:03> "Joe N2CX": BTW, N2CX pix shows me with filter mask since
my pulmonologist sez I'm allergic to solder smoke! Now I can solder
with no worries.
<20:48:36> "Alan W2AEW": Yikes! That's not a good thing to be
<20:51:21> "Alan W2AEW": Can I ask a naive question? Given that the
VCXO is phase locked to the GPS rx, what benefit is gained by
stabilizing the temperature of the VCXO? (sorry, I've missed
<21:05:18> "Mike WA8BXN": Dave obviously had a 30 m version because
we have the manual
<21:05:47> "Mike WA8BXN": elmer 101 never focused on 30 m version
<21:08:41> "Alan W2AEW": ...I think the LEDs in the Temperature
Display sub-circuit are drawn backwards...
<21:10:10> "Joe N2CX": Aha, maybe they are DED - Darkness Emitting
<21:10:55> "Mike WA8BXN": great idea for an Arduino!
<21:12:48> "Dave AA3UR": Very eager!
<21:16:23> "Joe N2CX": No surface mount so Doofusses need not apply!
<21:22:18> "Al - N8WQ": George, do you have plans to produce a
GPS-DO Motherboard to put this all together?
<21:25:10> "Alan W2AEW": I've also got a video on varactors,
including a VCO example:
<21:25:35> "George N2APB": I'm not surprised, Alan!
<21:26:07> "George N2APB": Al, I see your question here ...
<21:26:28> "Al - N8WQ": thanks
<21:27:12> "George N2APB": Yes, we're producing a motherboard for
the GPSDO, containing the different modules discussed thus far, as
well as the PLL "disciplining circuit" and output waveshaping
<21:28:13> "Al - N8WQ": cool, how about a bare board if we already
have the modules?
<21:28:40> "Pat - W0BM": On the Neo-7m, where do you tap off the 1
MHz timepulse to feed the PLL?
<21:31:55> "Pat - W0BM": yes
<21:36:41> "Al - N8WQ": Nice circuit (VVC) Joe, thanks for sharing
<21:37:56> "Mike WA8BXN": oven needed so vcxo drift less than time
constant of the control loop.
<21:38:50> "Mike WA8BXN": without oven and accurate frequency
measurement i could see frequency change when I caused air movement
walking by the vcxo
<21:38:21> "George N2APB": Perfect and succinct!
<21:39:56> "Steve, N0XC": Thanks guys! I always learn a bunch.
1. CWTD Analog
eBook at ...
1) Bode Plots are
commonly used in Amateur Radio (and all RF) circles to
graphically represent the performance of circuits ... Low Pass
Filters characteristics are the most often expressed using these
plots. The vertical axis is frequently expressed in dB, so
it seems appropriate to understand this fundamental ratio used
everyday among us hams.
Basic Op-Amp Configurations –
Short-cut diagrams for popular configurations. Op amps are used
in the I and Q channels of all Softrock designs, providing
precise gain in the two baseband audio paths after the Tayloe
3) Op Amp Bandwidth -- How
much gain can I get as freq. increases? (The gain of an op amp
stage decreases as the bandwidth spec is approached and
exceeded. Thus the “gain-bandwidth product” is an important
consideration in our designs.)
4) Small signal
step response – How bandwidth is related to rise and fall times
of square waves. For example a scope with a bandwidth of 1 GHz
has a rise time of 0.35 nS.
Instrumentation amplifiers – Special op amp circuits used for
small differential signals such as remote sensing and test
equipment uses – many temperature measuring devices use these.
6) Coax Cable
Information – A succinct listing of the important
characteristics of the coax types that hams use most. Great for
quick comparisons to see which is most suited to your particular
7) Coaxial Cable
Equations – If you have some unmarked coax cable here’s how to
tell what its impedance is. OTOH, if it’s marked Radio Shack
just sell it of at a hamfest….
measurement devices – Here are the common types of temperature
sensing devices. Common ones used in ham gear are thermistors
and diode sensors – in fact the temperature controller and temp
sensor in the CWTD OCVXO uses diode-based sensing and your water
heater may use a thermocouple.
9) Diode Voltage
Versus Temperature – Diode temp sensors are inexpensive and
cover a wide temp range. It only takes some tweaking to make
them useful- again look at the G0UPL temp controller used in the
10) Analog to
Digital and Digital to Analog Conversions – This the heart of
the techniques used to marry the analog world with the digital
domain. SDR’s are a prime example of the utility of these
conversions – heck your cell phone is a great example.
2. Now for the
... From the
CWTD Team ... (Click on any photo below to see a bigger mug
Mike WA8BXN Dave, AD7JT
Larry, K3PEG Craig, AA0ZZ Joe, N2CX
"The Scientist" "The Thinker" "The Elf" "The Doer" "The Brains" "The Dreamer"
GPS-Disciplined Oscillator Project
The breadboard platform ...
And the production motherboard pcb layout ...
Here is the original manual developed by SW30+
designer extraordinaire, Dave Benson, K1SWL.
CWTD SW30+ Manual: Theory, Assembly, Test,
Accessories ... Being spearheaded by Mike WA8BXN
The images below show examples of what we are developing right now
to assist in understanding and building the SW30+ Transceiver Kit.
It combines assembly, theory of operation and some great testing
steps all together into a very useful assembly and reference manual.
Optional Enclosure Kit
for the CWTD SW30+ Transceiver!
Big Surprise offering
from Craig AA0ZZ
Prototype #1 ...
The sides are a tad too long!
Example ... If you've seen Craig's
EZ keyer III project, you know how cool this will be!
Prototype build-up activities
Voltage-Variable Capacitance (VVC) Diode
Original SW30 calls for
MV1662 voltage variable capacitor
Difficult to find so wanted
to substitute MVAM109
SW30 oscillator operates at
2.42 – 2.45 MHz and beats with 7.68 MHz xtal osc
2.42 + 7.68 = 10.1 MHz,
2.45 + 7.68 = 10.13 MHz
Breadboarded SW30 tunable
oscillator to evalueate
Tables below show
equivalent freqs for samples of each VVC type
Inductor turns spread and
compressed to tweak frequency
Final range for MVAM 109 #
2 is 10.100 to 10.128 MHz
LO 10.130 10.130 10.125 10.125
HI 10.161 10.162 10.162
#3 #4 #5
LO 10.130 10.130
10.129 10.130 10.130
HI 10.159 10.158 10.160
Here are some of the publicly-available
materials produced by members of the QRP Community in the past ...
great reference and perspective!
(Click on any object below to
download the materials ...)
And the granddaddy of them all ...
Elmer 101 Special Issue of
QRPp magazine, Autumn 1998 ...
(Be careful, it's almost 50 MB in size!)
Some updates from Dave AD7JT and Mike
WA8BXN, who have been doing the bulk of the effort on this project
... design (Dave) and test (Mike)