This is a mirror of the old site from Sam Wetterlin. I have contacted him and he kindly gave me permission to host this valuable content. All credits go to him!
Sam Wetterlin Electronics

This site is presently dedicated to the posting of design information useful for amateur/hobbyist construction of electronic test equipment.





Following is a list of files containing schematics, board layouts or other useful information. Schematics and layouts should be considered works in progress.



Items related to Scotty’s Modular Spectrum Analyzer (MSA)


MSA OverviewAn overview of the MSA capabilities and construction, to provide orientation to potential builders.


Documentation for MSA Operation



The following documents walk the user through the actual use of the MSA, using simulated data. You do not need the MSA hardware to use these. They provide an overview of the MSA capabilities and an introduction to the use of the software.

Walk-Through: SA Mode

Walk-Through: VNA Transmission Mode

Walk-Through: VNA Reflection Mode


Bench-top Operating Guides

Spectrum Analyzer Operating Guide—MSA operating guide for Spectrum Analyzer Modes.

VNA Operating Guide—MSA operating guide for VNA modes. (Also includes SNA mode.)


Other Documentation

Operation of the MSA as a VNA—Overview and supporting documents regarding the MSA as a Vector Network Analyzer, including theory, procedures, fixtures, and test results.


RLC Analysis—Analysis of devices modeled as series or parallel combinations of a resistor, inductor and capacitor. Useful for measuring component values and parasitics.


Measuring PCB Dielectric Constant—Procedure and test results for measuring the dielectric constant of printed circuit boards from to 3 GHz, using the 1G, 2G and 3G bands of the MSA.

Measuring PCB Dielectric Constant Spreadsheet—Spreadsheet to help when matching resonant modes to measured peaks.

Fringe Effects in PCB—Experiments evaluating Fringe Effects that can affect the measurement of dielectric constant.


Measuring L and Q of High-Q Coils—Techniques for measuring inductance value and Q, especially for coils with high Q.


Front-End Compensation—New feature (as of 6/10) to adjust spectrum analyzer displays for the frequency characteristics of probes, amplifiers, attenuators or other front-end devices.


Version 116 ReadMe—Info on changes between MSA software versions 115 and 116 (scheduled for release Jan., 2011).


Filter MatchingDetermining optimum filter matching components using the Auto Match feature of the Two-Port module in MSA software version 116.


Effects of InterferenceAnalyzes the errors caused by various types of interference, such as the imperfect directivity of a bridge or leakage in switching mechanisms. Specifically analyzes the “VHF” Transmission/Reflection switch for the MSA.


PortView—A program for viewing and manipulating S-Parameter data, including a circuit layout module and a graphing module.


OSL Calibration—Collection of documents explaining the equations used for OSL calibration, the MSA method for describing calibration standards, information on construction of standards, and some test results. Specific data is provided for standards constructed with Amphenol RFX connectors and certain Molex connectors.


Marker Interpolation—Discussion of some issues arising when markers are placed between data points. Also illustrates some related features of the MSA.


Construction Photographs And Diagrams

Enclosure—Brass box to hold everything

High Frequency Grid Front

High Frequency Grid Back—The high frequency grid holds the microwave and signal generator components—DDSs, PLOs, Mixers and a few other modules. It is made of 0.016” brass strips reinforced on the back with small brass Tees. Very solid.

Progress 11/8/08—PDF file containing photos with most of the microwave modules installed.

Progress 12/3/08—PDF file with photos of the almost-finished innards. All modules are in place on brass grids, and most have their brass lids tacked in place. As is, this is functional enough for testing. Note: PDM inputs are reversed in this photo.

Module Layout and Coax Wiring—Modules viewed from bottom with coax connections. Express PCB format.

MSA Logic Wiring—Modules viewed from bottom with logic wiring. ExpressPCB format



MSA Documentation Relating to Hardware

RBW Filter Switch Board—Description and test results of switching board for selection of one of four RBW filters.


Video Filter Switch Board—Schematics and PCB layout (ExpressPCB formats) for automated video filter switching, and necessary corrections to the original PCB.


Calibration Accessories—Documentation, schematics and PCB files for several accessory boards that are useful for calibration of the MSA. Includes fixed attenuators, switched attenuators, calibration signal source and Leveler, most of which are described in more detail elsewhere on this site.


Control Board Tester—Zip file with program to set, clear or toggle the latches on the MSA control board via the parallel port. The latch bits can then be tested on a voltmeter or oscilloscope.


Calibration Source Schematic and PCB layout (ExpressPCB)

Calibration Source Test Results (pdf)—A simple device to generate a square or sine wave of predictable strength (near 0 dbm, accurate to +/-0.1 db) for spectrum analyzer calibration. The square wave is clean enough that a large number of odd harmonics also have very predictable values, which may be handy for other purposes. Built at several frequencies but output of 2 MHz is ideal for MSA calibration.


Peak DetectorExpressPCB layout of a high frequency peak detector; component values are shown on the layout. This might be useful for verifying the PLO output levels for anyone without a power meter.


High Frequency Log DetectorExpressPCB layout of a high frequency log detector; component values are shown on the layout. Has wider range than the Peak Detector.


Cavity Filter Tuning with the Peak or Log DetectorA procedure for tuning the cavity filter using the Peak Detector or Log Detector and a partially completed MSA.


Switchable Attenuator Schematic (ExpressSchem)

Switchable Attenuator PCB (ExpressPCB)

Switchable Attenuator Photo (jpeg)—Switchable attenuator with individually selectable attenuations of 2.5-5-10-20-20db which can be combined to cover 0-57.5 db in 2.5 db steps. This is intended to be used at 1 MHz for calibration of the MSA. At that frequency the attenuation should be accurate within 0.1 db at all settings. It is functional with somewhat less precision to at least 500 MHz.


Active Bridge for MSA—Documentation of an active reflection bridge that can also be used as a buffer amplifier in MSA test setups.

Buffer Amplifier—Buffer amplifier made by modifying the Active Bridge design. Great to 150 MHz; functional to 500 MHz.

ExpressPCB schematic and layout for Active Bridge and Buffer Amplifier. The layouts are provided for various op amp packages.


AGC LoopA high dynamic range method for amplification and magnitude measurement of the final IF in Scotty’s Spectrum Analyzer.  This is an alternative to the log detector.

Modifications to the original Cash Olsen AGC Loop boards to avoid oscillations (jpeg file)

SLIM version of AGC LoopNew layout and test results for modules in the SLIM format.


Expanded Log Detector

Updated Schematic and Layout for ExpandedLogDetector

Even More Updated Schematic and LayoutSimilar concept to the AGC loop, with slightly less potential range. A VGA is combined with a log detector (with a noise filter between them) to expand the effective range of the log detector. Combined with a preamp placed before the RBW filters (which preamp replaces the original IF amp), the range of the spectrum analyzer can be increased to cover -115 dbm to 0 dbm.


IF2 Amp—Amplifier with 28 dB gain, based on OPA847, to replace the standard MSA IF Amp, which provides 40 dB gain. This amplifier should be used when the Expanded Log Detector is used.


Digital Phase Detector Test—Schematic and test results of digital phase detector.  Test is at 20 MHz, but detector is functional to 100 MHz. Different logic family but similar to Scotty’s design.


High Voltage Supply Schematic

High Voltage Supply PCB—Schematic and PCB layout (ExpressPCB format) for a nominally +23V supply to power VCO control voltages, from a +10V source. It is a switching style design, but creates very little oscillator ripple at its input and output, and little radiation, though it should be encased with a fence and top. Output voltage can be adjusted.


1G/2G Diplexer—Documentation, schematic and PCB layout (ExpressPCB) for diplexer on Mixer 1 output to simplify switching between 1G and 2G modes. 1G is the normal 0-1 MHz mode. 2G mode is 1-2 GHz. 3G mode is 2-3 GHz and operates with the same hardware setup as 1G mode.


Cavity Filters (Cylindrical)

Cavity Filters (Box) –Construction method for cylindrical and box shaped cavity filters.


Stepped Phase Shifter—MS Word document describing a simple device for generating a test signal whose phase can be shifted manually or by digital command.  Can be used to calibrate a VNA or for other purposes.


SPI Transmitter Schematic

SPI Transmitter PCB   —PNG and ExpressPCB files for a simple device which can transmit data to SPI compatible devices.  Just push a series of 0’s and 1’s, and the necessary clock and data signals are generated.  Select signal can select one of three target devices.  Great for setting up digital attenuators, potentiometers, DDS’s, PLL’s, etc.  You don’t want to spend your whole life transmitting manually in binary, but it is a great way to test devices without messing with a computer hookup.


Attenuators Schematic

Attenuators PCB

Attenuators—Schematic (ExpressSchem), PCB layout (ExpressPCB),and PDF document describing homemade attenuators, with test results to 1.5GHz. These attenuators work extremely well—very accurate and very flat.



Fixtures/Reflection Bridges/Impedance Measurement


Measuring Resistance of Calibration Loads—Simple techniques to precisely determine the DC resistance of Loads used for OSL calibration. It’s easy with a 4 ½ digit DMM, but this explains how to get good results with the more common and much cheaper 3 ½ digit meters.


S21/Shunt Impedance Measurement—Measurement of impedance with the MSA using a normal transmission measurement (no OSL calibration) in a shunt test fixture. Describes the technique and test results.


Impedance Measurement with the Series Fixture and OSL Calibration—Description of simple test fixture for measuring impedance (and S11) of certain devices without use of a reflection bridge. The devices must be “floating” two-terminal devices (i.e. one terminal can’t be permanently grounded) such as resistors, capacitors, inductors and crystals. Test results show very good measurement from 1 ohm to 100K ohms, depending on frequency. In many cases the measurements are accurate to 500 MHz.


Shunt Fixture for Low Impedance Measurements—Simple fixture for impedance measurements as low as 0.01 ohms. Can be used with the MSA, or independently with manual calculations.


Fixture for Dip MeterSame shunt fixture, used with a coil for coupling to resonant circuits to measure resonant frequency. Can also be used without a VNA.


Three-Bead-Balun BridgeA reflection or return loss bridge which may be used in conjunction with Scotty’s Spectrum Analyzer configured with the VNA feature, or may be used manually as a freestanding bridge. Performance is good from 250 KHz to beyond 1 GHz. Note that for a second build of this bridge, I got somewhat lesser, but acceptable results. I prefer the “Bridge with Balun Plus Beads” described below.


Bridge with Balun Plus Beads—A reflection or return loss bridge that is ideal for use with Scotty’s Spectrum Analyzer configured with the VNA feature. Good from 50 KHz to beyond 1 GHz. Can also be used for manual measurements.

Single board PCB for Balun-Plus-Beads bridge—PCB layout (ExpressPCB) for the bridge, with input and output on one side and DUT on opposite side. Uses 1206 resistors so it can withstand modest “accidental power” (i.e. stray signals) at the DUT port.


Bridge with Dual TC1-1-13M


Performance GraphA reflection or return loss bridge useable with Scotty’s Spectrum Analyzer. Simpler than the ones above, but good only down to about 250 KHz, and not as good for manual measurements.


Manual Return Loss Measurements—Describes two bridges for manual measurement of return loss. The passive bridge (Parallel Line Bridge) is excellent from 1 MHz to 500 MHz, and quite functional to 1 GHz. The active bridge is outstanding from 10 KHz to 30 MHz and excellent to 300 MHz.

Using Manual Measurements to Estimate Impedance-PDF describing how to use multiple measurements of scalar return loss to determine impedance.

Spreadsheet for Impedance Calculation—Excel spreadsheet to do the graphs and calculations described above.


Bridge PCBs—PCB layout (ExpressPCB) for the above bridges.


Low Frequency Bridge—PNG--Image of schematic for a reflection bridge using one IC.


Simple Scalar Network Analyzer—Device to measure return loss/VSWR and transmission properties using a signal generator or sweep generator.  About $30 in parts.  Includes schematic, method of use, and some sample scans of filters and cables.


Reflection Bridge Schematic

Reflection Bridge PCB Layout—PNG and ExpressPCB files for a two op amp reflection bridge. Similar to Active Bridge described in “Manual Return Loss Measurements”, but uses +/-5V supplies.


Circulator Schematic

Circulator PCB Layout— PNG and ExpressPCB files for a circulator based on the Charles Wenzel article.


Visible Square Wave Reflections—Technique for viewing coax cable reflections using a square wave source and an oscilloscope. Can be used to find defects in the cable or its termination.



Bypass Tests—PDF file describing some tests of capacitor bypassing.


Quadrature Sampling-PDF describing a method of using quadrature digital sampling for phase and magnitude measurement of a low-IF signal for a VNA


ADE-1 Mixer as Phase Detector –Some experiments using the ADE-1 mixer as a phase detector, and potentially as a phase and magnitude detector.


Improve AD8302 with Phase Shifting—PDF file describing a method to use phase shifting circuitry to improve the accuracy of the AD8302 phase/magnitude detector, as well as to determine the sign of the phase, which the AD8302 always outputs as positive.


Expand AD8302 Range with AD8330 –MS Word file describing a method to combine a VGA with the AD8302 to expand its dynamic range.  The AD8302 nominally has a 60 db range, but is quite inaccurate at the edges.


AD995x Carrier Board—MS Word document describing a small carrier board for the AD995x DDS family, designed to confine intricate soldering to a single small board which can then be soldered onto a motherboard.


Test Results of Fancier Bridge—MS Word document showing results of experiments with reflection/transmission bridge using an AD8309 log amp to provide direct output measurement in db.


DDS Clock Calculator—Excel spreadsheet to calculate whether an integer multiple of the output of a DDS is also an integer multiple of the clock frequency, which aggravates spurs.  Assumes that the DDS has an output range centered at a user specified frequency, with a small excursion around that frequency, as when the DDS is used in a hybrid synthesizer to control a PLL.


Conversion of Phase Noise to Jitter—Excel spreadsheet to calculate the RMS jitter corresponding to a user-entered phase noise profile.  Can also be used in reverse to estimate how much phase noise corresponds to a specified amount of jitter.


VHF Noise Generator—Schematic for a noise generator for 100kHz to 30MHz and above.  Useful as a signal source to generate a DUT frequency response on a spectrum analyzer.





The Analyzer100, formerly the VectorAnalyzer60, currently in the prototype stage, is intended to be a stand-alone vector network analyzer for the 1kHz-100MHz range.  “Stand-Alone” means it requires no computer control.  It does depend on an external signal source for the test signal.  In this prototype, the phase or magnitude is displayed on the panel meters.  Ultimately, the displays will be microprocessor controlled. To see a further description, and the results of some tests, see Analyzer100.




Following is a list of useful links:


Scotty’s Spectrum Analyzer—web site explaining the original SSA and the Modularized Spectrum Analyzer.

Cash Olsen's Kits --kits for building Scotty’s Spectrum Analyzer, and related kits

SSA Builder’s Group --Builder’s group for Scotty’s Spectrum Analyzer


swetterlin at comcast dot net –My email address.  Comments are welcome.