sdr based test equipment - bay- · pdf filea different approach - tuned receiver the...
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SDR Based Test Equipment Beric Dunn, K6BEZ
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About Me
Beric Dunn K6BEZ
G7JUO in late 80s
K6BEZ since 2011
Interests are QRP & Building Stuff
RF Design Engineer for 19 years
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Background
“Build your own Antenna Analyser for under $20”
DDS based HF Antenna Analyser
2013 Pacificon
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Background
Ham Radio 360 Workbench build project
Group build project
Intro to using Arduino
www.360workbench.com/
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Limitations
Limited Frequency Range
HF Only
Sensitive to strong nearby signals
Detector has no selectivity, has no tunability
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Improve Frequency Range
Replace DDS with higher frequency module
Bridge/Detector circuit should work OK for 2m
Need Surface Mount for higher frequencies
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That Sensitivity Issue
Filter strong signal
AM band-block
What if strong signal is in ham bands?
Make test signal stronger
Add amplifier
What other similar products like MFJ-259 do
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A Different Approach - Tuned Receiver
The “$20 RTL Dongle” you might already have
Linear receiver with over 40 dB of dynamic range
25 MHz - 1.8 GHz frequency range
Lower with “Direct Sample” mode
Can be purchased for under $10
http://www.rtl-sdr.com/rtl-sdr-quick-start-guide/
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GQRX
Cross Platform
Can show 2 MHz spectrum chunk
from 25 MHz-1.8 GHz (with RTL-
SDR)
Can decode AM/FM/SSB...
Can’t show 2m band in one window
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More Bandwidth?
Enter RTL-Power
Step the RTL-SDR over freq range
Command line tool:
rtl_power -f 24M:1.7G:1M -g 50 -i 15m -1 noise.csv
2014-07-27, 23:15:29, 127000000, 129500000, 4882.81, 240, -30.74, -30.91, -29.60, -30.99, -30.80, -30.47, -31.04, -
30.57, -30.60, -30.65, -30.81, -30.02, -30.29, -30.59, -30.22, -29.96, -30.23, -29.96, -29.69, -29.79, -29.23, -29.92, -
29.46, -29.12, -29.54, -29.00, -29.04, -28.89, -27.95, -28.44, -28.18, -28.05, -28.38, -28.32, -28.16, -28.21, -27.59, -
27.80, -27.93, -27.50, -27.79, -27.43, -26.96, -27.34, -27.47, -27.52, -27.04, -27.15, -26.20, -26.05, -27.28, -27.15
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GUI wrapper for rtl_power
QSpectrumanalyzer (Linux)
https://github.com/xmikos/qspectrumanalyzer
Spektrum (Linux, Windows)
http://www.rtl-sdr.com/spektrum-new-rtl-sdr-spectrum-analyzer-software/
GUI for RTL Power (Windows)
https://sourceforge.net/projects/guiforrtlpower/
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What about the other half?
Most analysers have a signal source and a detector
Have the detector (RTL Dongle)
What about a signal source?
DetectorSignal
Source
Device
Under
Test
RTL-DongleFilter/Antenna?
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Bring The Noise
Natural enemy of Amateurs everywhere
Other than HOAs
Wide-band unwanted signal
Can it be used for good?
If we tune the detector, noise can become a useful signal source
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Noise Source
“BG7TBL”
12V in
Noise Out
$20 on Ebay
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Noise Source
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Filter Measurement
Filter passes noise in passband and rejects noise elsewhere
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Filter Measurement
No Filter With Filter
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Directional Coupler
The last piece of or puzzle
Taps of signal in 1 direction but not the other
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How can we use it?
Antenna measurements
Tap off reflected power
Dip in the noise shows where antenna is tuned
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Where do I get one?
ZEDC-10-2B / ZFDC-10-5
$50 from minicircuits, cheaper on ebay
Check frequency range
Check Impedance
50 Ohms NOT 75 Ohms
Can get surface-mount part for under $10
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Calibration
Remove slope from noise source so we are only measuring DUT
Take reference ‘thru’ sweep
Subtract this from measured data
Can do this in excel from RTL_POWER data
Slow, and not real-time
Or….
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Automate it!
Python - has libraries for everything - even RTL-SDR
Pyrtlsdr (https://github.com/roger-/pyrtlsdr)
Script it to Calibrate, measure and plot
python sdr_sweep.py <f_start> <f_stop> <number_of_steps>
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How Well Does it Work?
Demonstrate with Filter and Antenna
ADS-B 1090 MHz Band Pass Filter
Dual Band Antenna
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Filter Measurement
1090 MHz Band Pass Filter
“passes 980 MHz – 1150 MHz
a 40dB drop outside the pass band”
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Filter Measurement - Results
“passes 980 MHz – 1150 MHz
a 40dB drop outside the pass band”
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Results - Antenna Measurement
Ed Fong J-Pole
2m & 70cm
On roof of my house through about 25’ of RG-8X
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Results - Wide Sweep
Dips at about
150 MHz
450 MHz
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Results - Zoom in on 2m
$50 (SDR+Noise+Coupler) $15000 Anritsu SiteMaster
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Results - Zoom in on 70cm
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$50 (SDR+Noise+Coupler) $15000 Anritsu SiteMaster
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Next Steps
Modify Derek AG6PO’s code for the Ham Radio 360 Analyzer to include this
Run on Raspberry Pi with touch-screen
Try to get working with Direct Sample mode (HF!)
Make PCB with noise source and coupler built in…..?
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Thank You!
Any Questions?
Presentation Materials: https://k6bez.blogspot.com/
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