November 17, 2015

CWTD Episode #76

Analog Dialogue
An "Analyze This!" style discussion of a fabulous resource from Texas Instruments

And updates on:

GPS-DO Project  ....  Elmer 101 Course  ....  SW30+ Kit  ....  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 experimenters. 

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 your workbench!

73, George N2APB and Joe N2CX

Podcast ... Click to play, or right-click to download and archive on your computer

Chat window comments made during the show ...

<20:03:57> "Alan W2AEW": link:
<20:07:09> "Alan W2AEW": Nice to be here (sitting in a hotel room in MA)
<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 product too)
<20:25:33> "Mike WA8BXN": we may see something like this in the SW30+
<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 rise/fall times)
<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 allergic to!
<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 previous episodes)
<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 Diodes!
<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 circuits!
<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 your experiment
<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 Dialogue!

               Download eBook at ...
                                           or ...


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.



2) 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 Detectors.







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.


5) 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 application.


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….


8) Temperature 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 CTWD OCVXO.                                                                              


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 Project Updates!

... From the CWTD Team ... (Click on any photo below to see a bigger mug shot!)

       Mike WA8BXN                Dave, AD7JT                     Larry, K3PEG                     Craig, AA0ZZ                Joe, N2CX                   George, N2APB
       "The Scientist"                 "The Thinker"                        "The Elf"                            "The Doer"                  "The Brains"                   "The Dreamer"


1)  GPS-Disciplined Oscillator Project

The breadboard platform ...

The prototype ...


And the production motherboard pcb layout ...


2) SW30+ Transceiver Kit

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 ... Mike, WA8BXN



Voltage-Variable Capacitance (VVC) Diode Characterization ... Joe, N2CX

MVAM109/MV1662 Comparison

-          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


                   #1          #2       #3        #4

LO           10.130   10.130  10.125   10.125

HI            10.161   10.162   10.162   10.162



                  #1         #2         #3        #4         #5

LO           10.130  10.130    10.129  10.130  10.130

HI            10.159  10.158    10.160  10.160 10.157



3) Elmer 101 Course

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!)

4 GPS Display Terminal

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)