CWTD - Dec 10, 2013

(Now a bi-weekly program)

December 10, 2013

Poor Ham's Scalar Network Analyzer (PHSNA)
A study of a simple scalar network analyzer (SSNA) project, and interview with the PHSNA designers: N5IB & W5JH

Left: Arduino controller, DDS signal source, LPF and buffer amp                   .
Right: RF Power Meter, containing the logamp power sensor and buffer amps.

Overview

Being the intrepid homebrewers and experimenters that we all are here in CWTD, we are always on the lookout for simple measurement equipment that can be used for giving us greater insight to the radio projects on our benches.

Well, several months ago N5IB and W5JH teamed up to work on developing a useful-and-inexpensive way to sweep an RF signal through a Device-Under-Test (DUT) and read and plot the power coming back from the DUT, yielding insightful characteristic information about it.

We have been following the PHSNA project as it has been evolving with its Yahoo Group followers and we wanted to explore some of the background information here with our CWTD members and get some "insider knowledge" from the masterminds behind the project!

73, George N2APB & Joe N2CX

Audio Recording ... (Click to listen or download)

Discussion Notes:

<20:15:31> "Joe N2CX": Yahoo PHSNA group - http://groups.yahoo.com/neo/groups/PHSNA/conversations/topics
<20:31:49> "George - N2APB": Joe ... you have a technical question or two along these lines? Pop in when Jim is done?
<20:40:04> "Charles WC5MC": Good, if you don't program in C how can you call yourself a programmer? ;)
<20:49:49> "Rick K3IND": ?
<20:55:46> "Steve K1RF": sorry about that. I've been in and out and this may be extra bandwidth, but what is the difference between an SNA and a spectrum analyzer with a sweep generator?
<20:58:04> "Alan W2AEW": a spectrum analyzer + tracking generator uses a narrow-band, tuned detector, while the SNA uses broadband RF power detection. Thus, the SA+TG can typically have lower noise floor, higher dynamic range.
<20:59:10> "Steve K1RF": ahh....makes sense. Thank you.
<21:04:13> "Terry WB4JFI": Yes, use either an ERA3 or MAV11 MMIC
<21:10:41> "Charles WC5MC": vox threshold?
<21:11:20> "Terry WB4JFI": Jack, was that the small Brainerd 6-stage BPF board, and did you use SMT or torroid coils?
<21:11:53> "Joe N2CX": I think you may be speaking too close to the mic and clippping out on voice peaks. I've done that myself!
<21:11:55> "George - N2APB": I have the Brainard filter board here too.
<21:13:42> "Jack -- W0FNQ": Terry, no I have Dave's board but haven't tried it yet. Check on http://mobokits.stormwarning.org/content/mobo-links-0 for some information on the MOBO filters
<21:15:23> "Joe N2CX": Jim, can you send me the web link that Nick is talking about?
<21:15:30> "Charles WC5MC": Method of least squares?
<21:19:10> "Nick WA5BDU": Here you go -- method of least squares ... http://science.widener.edu/svb/stats/regress.html
<21:32:59> "Armand WA1UQO": Thanks Guys. Have a great Holiday And Happy New Year!
<21:33:01> "Nick WA5BDU": dit dit
<21:33:37> "Terry WB4JFI": Another great show!
<21:33:48> "Mike W5RST": 73
<21:34:37> "Larry - W2HHV": Another AD9850 module seller on ebay (Qty 2 for $8.88 + $.60 shipping) <http://www.ebay.com/itm/2PCS-AD9850-DDS-Signal-Generator-Module-0-40MHz-2-Sine-Wave-And-2-Square-Wave-/400385386770?pt=LH_DefaultDomain_0&hash=item5d38d42912>

CWTD Episode #66: Poor Ham's Scalar Network Analyzer

... A simple scalar network analyzer employing an Arduino UNO, an inexpensive AD9850 DDS module, and an AD8307 RF power detector

PHSNA designers and guest hosts with us for this episode:



                    Jim N5IB                                    Jerry W5JH

Features / Design Goals:

USB interface to PC (appears as a COM: port)

Use with a terminal program such as Term232, TeraTermPro, HyperTerm, etc

Frequency range from 1 MHz to 30 MHz

1 Hz frequency resolution

Selectable step size from 1 Hz to (End Frequency – Start Frequency)

Sweep speed about 100 steps per second

Buffered, filtered output at about -10 dBm level (0.1 mW or 70 mV across 50 ohms) can be modified for more or less output

Dynamic range ~ 55 to 60 db

Two analog input channels, user adjustable analog reference voltage

Menu-driven user interface

Requires a single 12 V DC supply

Data analysis with Excel® or other graphing application, e.g., (Graphical Analysis®)

Open source – program code released for experimentation

BLOCK DIAGRAM

                                                               Block Diagram

SCHEMATIC

         Alternate DDS buffer amplifier

PROTOTYPES

Another version built by N5IB ...
This Arduino+DDS assembly is housed in a nice wooden enclosure, characteristic of Jim's fine handiwork.



                                                     RF Power Meter Board

PLOTS, GRAPHS and OTHER REPORTING METHODS

ALTERNATIVES

"Low power sweeping & measurement" can be accomplished in a number of different ways ...

1) Sweeper Input Card + Micro908 Antenna Analyst



            Sweeper Input Card (SIC) developed in early 2013 on CWTD                                                               SIC mounted inside the                              Making measurements on a Filter-Under-Test
            (Has shielded log amp for input, and 12-bit ADC output to a processor.)                                             Micro908 Antenna Analyst

2) SIC Sweep = Sweeper Input Card + DDS + Arduino (modified WA5BDU_1r5) = "PHSNA Hybrid"

REFERENCES

SSNA Yahoo Group (open membership – support documents will be posted here) ... http://groups.yahoo.com/group/PHSNA

Arduino UNO® Support:   http://arduino.cc/en/Main/ArduinoBoardUno

AD-9850 Modules (a selection of overseas eBay sources):
    http://tinyurl.com/puhqa75
    http://tinyurl.com/pxxrxjh
    http://tinyurl.com/nfbhw5h
Schematic: http://tinyurl.com/o63l2t3
W7ZOI RF Power Meter (QST June 2001, available in print archive for ARRL members) ... http://w7zoi.net/Power%20meter%20updates.pdf
Analog Devices AD-9850 DDS datasheet: ... http://www.analog.com/static/imported-files/data_sheets/AD9850.pdf
Analog Devices AD-8307 RF Power Detector Datasheet ... http://www.analog.com/static/imported-files/data_sheets/AD8307.pdf
Graphical Analysis for Windows – scientific graphing application ... http://www.vernier.com/products/software/ga/