March 10, 2015
Scalar Network Analyzers
A review of some useful techniques and instruments for performance measurement of "networks"
(like filters, crystals, receivers, antennas, and more),
with a close-in look at a recent homebrew project called the "SNA".
Welcome! We have a guest designer joining us in this episode ... Dave Collins, AD7JT, will walk us through the topic of measuring a circuit's behavior to an RF stimulus, and his exciting new homebrew design of a super-useful instrument for doing this called the Scalar Network Analyzer. The SNA is a handheld instrument with a color graphic display (with a touch screen!) that enables the user to measure performance of things like LPFs, crystals, and receivers, while also serving as a precision RF signal source and an accurate RF power meter!
Listen to the Podcast (Right-click and download to your computer for best listening results)
Chat Text from during the show ...
<20:20:16> "Bruce - N1RX": Great news about the SW+ kit reintroduction! It has long been the "best bang for the buck" in QRP. (IMNSHO)
<20:20:39> "Ray K2ULR": I like the SW-30 idea, too.
<20:22:36> "AC0BQ": Ge all. I'm good for the 30 m version!
<20:25:27> "Joe N2CX": DUT = Device Under Test
<20:33:17> "Bruce - N1RX": SARK-110 from SteppIR "pre-order" stated "due Jan 2015" They -may- be available from stock now...
<20:42:39> "AC2GL_Dave": Any plans to re-roll the design using an AD8302?
<20:46:09> "George N2APB": Haven't considered that device. What benefits?
<20:52:37> "Clint-ka7oei": I always wondered how one dealt with the 180 degree ambiguity on the '8302...
<20:59:02> "Bruce - N1RX": WELCOME ABOARD, N8ET!
<21:00:03> "Joe N2CX": N8ET - good to see you with us, Bill!
<21:01:01> "George N2APB": Great to see you Bill. Be sure you are looking at our "whiteboard" of slides and visual, located at http://www.cwtd.org/SNA/2015-03-10.html
<21:04:13> "Mike WH6YH": Very Interested in Ver4
<21:04:34> "George N2APB": Thanks Joe - good job!
<21:06:05> "George N2APB": Yes, ver 4 is WAY cool. Plus, one can build up (add on) the different capabilities on the original NAT pcb ... OR, as we'll explain here this evening, there is a new "SNA" board coming along with all the hardware capabilities on the board already ... no mods! ;)
<21:08:20> "Bruce - N1RX": I'll probably hold off building my V3, in favor of a new V4 board... 8-)
<21:08:59> "Jim N5IB": Mike (WH6YH) see eBay item # 201114847196 for 8307 ten for $7
<21:10:05> "Bruce - N1RX": I still have free samples of the AD8307 from A/D waiting to be used....
<21:24:06> "Mike WH6YH": Lots of great work from those involved with designing this. :^))
<21:26:24> "George N2APB": Jim N5IB, Can you describe a little bit about the Measurement Receiver?
<21:26:41> "Jim N5IB": sure...
<21:27:58> "Jim N5IB": folks should see the PHSNA Yahoo group site for a document on the measurement receiver (a W5JH creation)
<21:28:28> "AC2GL_Dave": @George: The 8302 has the ability to give the phase angle as well as magnitude
<21:30:28> "Jim N5IB": It was Jerry W5JH who did the Meas Rx that I made PC boards for, taken from EMRFD
<21:31:24> "Mike WH6YH": Jim, can you post a link for the boards?
<21:31:53> "Jim N5IB": All out of boards for the moment...
<21:32:55> "Bruce - N1RX": An excellent useof the crystel parameter measurement is selecting crystals for the SWL+ reintroduction.
<21:38:23> "Jim N5IB": May be giving a PHSNA talk at HamCom, but not sure if it will make the schedule...
CWTD Episode #71: Scalar Network Analyzer
A) First, let's recap ... The road we've traveled, and the road laying ahead
Why we do this ... At-Scale Elmer'ing
Brief recap of past episodes
The CWTD "approach & style"
How listeners can interact (live and via podcast)
Value and benefit that can be derived from this growing wealth of technical materials, etc.
Our Plan for the Year!
B) What's New Out There? ... Cool new happenings, devices, rigs, gadgets & projects
Presentation Roundup 2015:
George N2APB is presenting the SNA Project at the Trenton Computer Festival on March 21
Joe N2CX is presenting the CWTD Elmer 101 & SW40+ Project at the South Jersey Radio Association (SJRA) monthly meeting on April 22
Dave AD7JT is presenting the SNA Project at the OzarkCon QRP Conference on April 10-11
Dave AD7JT and George N2APB are presenting the SNA Project at the TAPR Digital Communications Conference in September
George N2APB is presenting the SNA Project at the Pack Rats VHF Conference in Philadelphia on Oct 3
SARK 110 - http://www.sark110.com/ .... ~$390
Portable analyzer with graphical display
Similar in principle to AIM-4170
Now available at SteppIR
MFJ 225 antenna analyzer/VNA .... ~$300
Portable or bench VNA
You kits FG-01 Antenna Analyzer from TenTec
http://www.tentec.com/fg-01-antenna-analyzer-1-78-mhz-includes-battery/ .... ~$259
Includes graphical display
The FG-01 with its color graphical display allows you to dial in the frequency you wish to operate on and immediately read the SWR and Impedance of the antenna at that frequency. The FG-01 also allows you to easily adjust the frequency to determine the desired SWR points of the antenna. For instance if you wanted to know the 2:1 limits of your antenna you would just change the frequency using the large knob to move the graph to the 2:1 point on the center of the display and read the frequency.
Mini Radio Solutions Bluetooth VNA
Available thru HRO - http://www.hamradio.com/detail.cfm?pid=H0-012128 .... ~$490
The mini-VNA Pro BT is a further development of the worldwide highly acclaimed mini-VNA Network Analyser. The most prominent enhancements are a built-in Lithium Ion battery and the new Bluetooth interface. Both enhancements allow you to use the mini-VNA Pro BT outdoors, directly at the base of the antenna.
Further functions and technical data of the mini-VNA Pro BT
•Frequecy range 0.1 to 200MHz
•Calibration using open/short-load for accurate results
•Range of impedance Z from 1 to 1000 Ohms
•Two ports VNA with S11 and S12 display; displayed and save results
•I/Q DDS Generator with 0 dBm output power
•Two separate RF outputs for I/Q for SDR experiemnts and IMD measurements with independant attenuator from 0 to 55dB, phase angle adjustable to 1° precision
•Built in Bluetooth® Adaptor (Class 1) for wireless remote measurements
•Built in LiIon 1000mAh battery, (4 hours full-scan operation)
•Built in battery charger (up to 400mA)
•Accessory port for future optional interfaces and frequency extenders
•Low power consumption, 220mA @3.6V, (analyser mode using USB port)
•Power save mode
•SMA connectors for better isolation
•extended dynamic range: up to 90dB for transmission, up to 50dB for reflection
•Boot loader for future firmware upgrades
•User friendly interface for PC Windows, Linux and MAC
•Integrated Smith Chart in software
•Measurements of motional crystal parameters, cable lengths & more
•Export data in several formats: JPG, Excel, ZPLOT, S2P, PDF
Several QRP rigs including MTR by KD1JV
Trail friendly 10/20/40 End-Fedz - http://www.lnrprecision.com/endfedz/trail-friendly/
New EZ Quad 10/15/20/40 End-Fedz - http://www.lnrprecision.com/endfedz/
Hewlett-Packard / Agilent 8757D
The Agilent 8757D has four independent display channels that process the signals from the Agilent 85037 series precision detectors, 85025 and 85026 detectors, and the 85027 series directional bridges for logarithmic display, in single channel or ratio mode. Three (optionally four) detector inputs are provided.
The Giga-tronics 8003 Precision Scalar Analyzer combines a 90dB wide dynamic range with the accuracy and linearity of a power meter in a single instrument. Measures active and passive components with power meter accuracy from 10 MHz to 40 GHz. AC and DC detection is available with equal accuracy on the 3 inputs and standard, high-power, true RMS, low VSWR and triggerable pulse power sensors are available. Additionally, precision CW return loss bridges are available
C) Now, some "background" ... to RF measurement techniques
Contain a source & multiple receivers
Display amplitude (and sometime phase) ... often in a ratio
Look for a known signal at the output of the D.U.T. in a "stimulus-response system"
Enable designers to see many aspects about the performance of a component or network
Common Terms for HF Device Characterization
Scalar Network Analyzer
As the name indicates, a scalar network analyzer or SNA is a form of RF network analyzer that only measures the amplitude properties of the device under test. In view of this it is the simpler of the various types of RF network analyzer.
Effectively, a scalar network analyzer, SNA, works just as a spectrum analyzer in combination with a tracking generator. When a tracking generator and spectrum analyzer are used together, their operation is electrically closely linked.
The tracking generator generators a swept signal on exactly the same frequency that the spectrum analyser is receiving. Thus if the output from the tracking generator was connected directly to the input of the spectrum analyzer, then a constant line would be seen across the screen of the analyzer indicating the amplitude of the tracking generator output.
If a device is placed between the two items, then the spectrum analyzer will note any amplitude variations. In this way for example, the response of a filter can be plotted. The constant output of the tracking generator will pass into the filter, where the response of the filter will change it according to the frequency and the response of the filter at that frequency, and in this way the spectrum analyzer will be able to display the response of the filter. From this it can be seen that scalar network analyzers, SNA, are very useful for measuring the amplitude response of a variety of components.
Vector Network Analyzer
The vector network analyzer, VNA is a form of RF network analyzer widely used for RF design applications. A vector network analyzer is a test system that enables the RF performance of radio frequency (RF) and microwave devices to be characterized in terms of network scattering parameters, or S parameters. The information provided by the vector network analyzer VNA is then used to ensure that the RF design of the circuit is optimized to provide the best performance. Using an RF network analyzer in any RF design provides the RF design engineer with a view of the components and circuits that would not be possible with any other form of test equipment. In this way the vector network analyzer, VNA is an essential tool that RF design engineers should be able to use.
Although the name of the vector network analyzer VNA is the most widely used name for this item of test equipment, sometimes it may be called a gain phase meter in view of the fact that they are able to measure both the gain, i.e. amplitude and also the phase of the device or item under test. Another name that is occasionally used is the Automatic Network Analyzer. However by far the most widely used is the name vector network analyzer, VNA.
Logarithmic RF Detectors ... a common approach
AD8307 ... (Analog Devices data sheet: http://www.analog.com/media/en/technical-documentation/data-sheets/AD8307.pdf )
The AD8307 is the first logarithmic amplifier made available in an 8-lead (SOIC_N) package. It is a complete 500 MHz monolithic demodulating logarithmic amplifier based on the progressive compression (successive detection) technique, providing a dynamic range of 92 dB to ±3 dB law-conformance and 88 dB to a tight ±1 dB error bound at all frequencies up to 100 MHz. It is extremely stable and easy to use, requiring no significant external components. A single-supply voltage of 2.7 V to 5.5 V at 7.5 mA is needed, corresponding to an unprecedented power consumption of only 22.5 mW at 3 V. A fast acting CMOS-compatible control pin can disable the AD8307 to a standby current of less than 150 µA. Slope of 25 mV/dB,
1 μW TO 1 kW 50 Ω POWER METER ... A Typical application in Amateur Radio
The front-end adaptation shown in Figure 41 provides the measurement of power being delivered from a transmitter final amplifier to an antenna. The range has been set to cover the power range −30 dBm (7.07 mV rms, or 1 μW) to +60 dBm (223 V rms, or 1 kW). A nominal voltage attenuation ratio of 158:1 (44 dB) is used; thus the intercept is moved from −84 dBm to −40 dBm and the AD8307, scaled 0.25 V/decade of power, now reads 1.5 V for a power level of 100 mW, 2.0 V at 10 W, and 2.5 V at 1 kW. The general expression is
P (dBm) = 40 (VOUT − 1)
The required attenuation can be implemented using a capacitive divider, providing a very low input capacitance, but it is difficult to ensure accurate values of small capacitors. A better approach is to use a resistive divider, taking the required precautions to minimize spurious coupling into the AD8307 by placing it in a shielded box with the input resistor passing through a hole in this box, as indicated in Figure 41. The coupling capacitors shown in Figure 41 are suitable for f ≥ 10 MHz. A capacitor can be added across the input pins of the AD8307 to reduce the response to spurious HF signals, which, as previously noted, extends to over 1 GHz.
The mismatch caused by the loading of this resistor is trivial; only 0.05% of the power delivered to the load is absorbed by the measurement system, a maximum of 500 mW at 1 kW. The post demodulation filtering and slope calibration arrangements are chosen from other applications described in this data sheet to meet the particular system requirements. The 1 nF capacitor lowers the risk of HF signals entering the AD8307 via the load.
D) And now ... the SNA! ... Featuring SNA designer Dave AD7JT!
It all started with the ...
Features & Specifications
Basic NAT Block Diagram (versions 1 & 2)
Menu Mode Screen Shots
PLX Mode Screen Shots
DOS Mode Screen Shots
SCALAR NETWORK ANALYZER ... Version 4
NAT-SNA: NAT Scalar Network Analyzer ... BLOCK DIAGRAM
RF Power Meter by Dick Faust, K9IVB ... http://www.k9ivb.net/RF_Power_Meter/
The "SNA Power Meter"
Antenna Analysis with Return Loss Bridge (RLB)
Crystal Characterization & Matching
How about a little math? ... ;-)
RF Network Analyzer Basics Tutorial
SNA Slide Deck ... SNA_(AD7JT-N2APB)_CWTD.pptx
NAT-SNA Home Page & Kit Availability ...http://www.midnightdesignsolutions.com/nat
NAT-SNA Yahoo Group ... https://groups.yahoo.com/neo/groups/NAT-SNA/info
PHSNA Yahoo Group ... https://groups.yahoo.com/neo/groups/PHSNA/info
Contact the SNA Designers: