This site is
presently dedicated to the posting of design information useful for
amateur/hobbyist construction of electronic test equipment.
FILES
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
Construction Photographs:
Enclosure—Brass
box to hold everything
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
Progress
11/8/08—PDF file containing Photos with most of the microwave modules
installed.
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.
1 MHz
Calibration Source Schematic (ExpressSchem)
1 MHz
Calibration Source PCB layout (ExpressPCB)
1 MHz 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.
Peak Detector—ExpressPCB 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.
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.
AGC Loop—A 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 Loop—New layout and test results for modules
in the SLIM format.
Expanded
Log Detector—Similar 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.
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 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.
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 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 (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.
PortView—A
program for viewing and manipulating S-Parameter data, including a circuit
layout module and a graphing module.
Reflection
Bridges
Three-Bead-Balun
Bridge—A 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, but is not as good for that purpose as the ones below.
Bridge with Dual TC1-1-13M
Performance
Graph—A 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 (
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 PCB Layout—PNG and ExpressPCB files for a two op amp reflection bridge.
Similar to
Circulator PCB
Layout— PNG and ExpressPCB files for a circulator
based on the Charles Wenzel article.
Other
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.
Analyzer100
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.
LINKS
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
sam
at wetterlin dot org –My email address. Comments are welcome.