Copyright © 2009, 2010 Stu Phillips – K6TU Woodside, CA November 4 th , 2010 First presented September 2009 Weak Signal Propagation Reporter and Some of the things you can do with it!
Copyright © 2009, 2010 Stu Phillips – K6TU
Woodside, CA
November 4th, 2010First presented September 2009
Weak Signal Propagation Reporterand
Some of the things you can do with it!
Stu’s Background Engineer, now Venture Capitalist & Business Consultant
Systems, Software & Communications
ICL, Logica, Tandem Computers, Cisco Systems
First licensed as G8HQA in UK, 1973
Lived in California since 1984
US license in 1988 – N6TTO
Changed call in 2009 – K6TU
Ham Interests Weak Signal Propagation
Contesting
Ultra accurate time & frequency
Combining computers & radio (digital modes, SDR…)
Weak signal operation on HF
Bottom of the Solar Cycle
Propagation is “bad” – but how bad?
Test the limits of what can be done
Low power (QRP - < 5W, QRPP – mW)
RX signal often too weak to copy by ear
Use DSP software to recover signals below noise
Spectran, Argo, Spectrum Lab
Operating modes
QRSS – very slow CW (3 second dit or longer)
Weak Signal Propagation Reporter (WSPR)
WSPR Designed by Joe Taylor – K1JT for weak signal propagation operation
Implemented as a Windows program using PC sound interface for A/D and D/A
Combines Slow data rate (1.46 baud)
Forward Error Correction
Redundant coding & integrated timing symbols
4 level FSK at 1.46 Hz shift per level
Recover signals to ~ -28 dB SNR Too weak to hear, barely visible on waterfall
Simple message payload Call sign, Maidenhead locator, Transmit power in dBm
Uploads received signal “spots” to WSPRnet.org Freely accessible
Central Database for WSPR spots (www.wsprnet.org)
Set frequencies for WSPR operation to maximize chance of “spots”
WSPR – the program
Uploads spots
Spots from the database
WSPR operation
Low power, 5 watts – preferably less
5 W will generate spots across the world on 30m
Transmit, check database for spots
Receive, upload spots of received stations
Addictive!
So… what can you use it for ???
WSPR uses
Entertainment!
Testing different antennas
Validating propagation predictions
…
The challenge
How far could I get on 200 mW or less?
Built home brew WSPR transmitter
QRP crystal controlled transmitter
PIC controller
Generates WSPR signal
Timing control via GPS
Crystal oven controller for stability
Switches external attenuators
Transmit WSPR signal on 10.140 MHz
200 mW (23 dBm), 50 mW (17 dBm), 10 mW (10 dBm)
See http://1vc.typepad.com/ethergeist for details
How I got into this…
2009-04-03 23:52 WB3ANQ 10.140191 -29 0 FM19rc 0.005 VK6DI OF88cd 18609 301
WSPR spot from database
VK6DI reports hearing WB3ANQ at -29 dB SNR
Distance of 18,609 Km (short path)
WB3ANQ transmitting at FIVE MILLIWATTS
My best spot from VK6DI
2009-03-17 08:46 N6TTO 10.140186 -25 0 CM87vk 0.05 VK6DI OF88cd 14720 258
-25 dB SNR at 14,720 Km on FIFTY MILLIWATTS
How the heck did WB3ANQ do that????
Must be the antenna
N6TTO
Inverted L (160m full size) loaded with remote ATU
Sub-optimal radial screen
WB3ANQ
Force12 Sigma-40 vertical dipole
How differently do these antennas behave on 30m????
Antenna modeling
Computer modeling and analysis of physical antenna design
to predict
Radiation pattern
SWR
Feed impedance
Easy to use – graphical interface
Fast - seconds to try different configurations
Inexpensive
EZNEC (http://www.eznec.com/) $139
4NEC2 (http://home.ict.nl/~arivoors/) FREE
EZNEC analysis – Inverted L
Describe antenna as a series of wires
Graphic view of
constructed wires
EZNEC analysis – Inverted L
Run SWR analysis
Plot the results for SWR and Far Field radiation
EZNEC Analysis – Inverted L
SWR analysis for 1.8 MHz
Main radiation lobe at 25 degrees
Elevation angle
But how does it radiate on 30m?
Looks like a cloud warmer!!!
Peak radiation angle 35 degrees towards VK6
EZNEC analysis – Inverted L
EZNEC analysis – Force12 Sigma40
Low angle of radiation
17 degrees over normal
ground
Must be the antenna!!!
The “solution”
Build a 30m vertical and try it out
Cheap and cheerful approach
Wire antenna hung from tree
Use X shaped end loading to fit into available space
16 degree radiation angle – sweet!!!!
Comparing two antennas with WSPR
Use the same transmitter (200 mW)
Run each antenna for a week
Solar minimum an advantage – little variation in propagation
Extract the data from the WSPR database
Plot the results
Better test would have been alternating transmissions on each
antenna but this was quicker to get going!
Results – Inverted L(<
= -
29)
Seri
es5
Seri
es9
(4 -
6)
0
2000
4000
6000
8000
10000
12000
14000
16000
0:12 1:
30 4:12 5:
00 6:18 7:
18 8:06 8:
54 9:42
10:1
8
11:0
0
11:4
2
12:1
8
13:0
0
13:3
6
14:1
8
15:0
615
:54
16:3
017
:18
18:1
819
:42
21:0
022
:18
23:4
2
14000-16000
12000-14000
10000-12000
8000-10000
6000-8000
4000-6000
2000-4000
0-2000
WSPR Spots for N6TTO
23 dBM to 160m Inverted L
3/1/09 0000Z -> 3/10/09 23:50Z
Results – Vertical Dipole
0
2000
4000
6000
8000
10000
12000
14000
16000
14000-16000
12000-14000
10000-12000
8000-10000
6000-8000
4000-6000
2000-4000
0-2000
WSPR Spots for N6TTO23 dBM to 30m Vertical Dipole
3/11/09 2350Z -> 3/22/09 19:26Z
Surprise! The “cloud warmer”
works better at long ranges than the Vertical Dipole
Could be terrain – path to Australia from my QTH goes straight into rock
Higher radiation angle an advantage but results in more hops (weaker signal at distance)
Could it be propagation? Propagation can be modeled too!
Modeling tools can predict
Number of hops for a given path
Receive signal to noise levels for given power & antenna combinations (TX and RX)
PC based software – inexpensive or free
Graphical UI
Learning curve a little steeper (more variables)
Fast – 10‟s of seconds
Inexpensive to moderate price
VOACAP (http://www.voacap.net) FREE
PropLab Pro (http://www.spacew.com) $240
VOACAP Developed by US Government for coverage predictions of Voice of America radio
broadcasts
Extensive help/tutorial information available on the Internet
Three propagation models VOCAP (original)
ICEPAC (modified to include effect of K index)
REC533 (ITU RS Recommendation 522)
Point-to-point or Area coverage calculations Area coverage gives SNR or other parameter maps – easier to interpret!
Basic input data Solar weather
Transmitter & Receiver locations
Transmitter power & antenna
Receiver antenna & local noise level
Parameters to be calculated (SNR, received signal level…)
Required reliability – CRITICAL!!!!
Combine modeling tools Use ICECAP – takes into account planetary K (Kp) as well as SSN
ICECAP models propagation taking into account the transmitter and receiver antennas
Uses a form of antenna description that specifies antenna gain, radiation angle by direction (azimuth)
EXNEC and 4NEC2 can both save described antennas in the file format (type 13) required by VOACAP
For EZNEC Define the type of ground Select 3D plot mode Set step size to 1 degree Run Far Field analysis Save modeled antenna as type 13 file to VOACAP folder
Critical – model Y axis is the NORTH-SOUTH axis
Prediction run for WB3ANQ Model the WB3ANQ Force12 vertical dipole
Save in type 13 file
VK6DI located in a very quiet (remote!) area of Western Australia
Antenna at VK6DI is a horizontal dipole
Determine Lat/Long coordinates for each station
Determine the ground conditions at WB3ANQ
Pick date/time for run
Use Solar weather data for that date
Configure ICEAREA & run the model
WB3ANQ Ground
WB3ANQ located in
Pasadena, MD
Close to river estuary
Water table at 2 to 3
feet below ground
VERY good ground
Ground effect on Force12 Vert. Dipole
Normal ground – radiation angle 17 degrees
Very good ground – radiation angle 10 degrees
Setup ICEAREA
Plot the results and scale
VOACAP limitation – won‟t calculate for powers below 0.1
watt – calculate for 0.1 watt and scale result
Have to convert WSPR SNR (db in 2.5 KHz bandwidth) to
SNR in 1 Hz bandwidth for VOACAP
WSPR -28dB in 2500 Hz = -62 dB in 1 Hz
Then scale SNR levels to accommodate power reduction
from 0.1 watt to 5 milli-watts
Need 13dB better SNR than VOACAP predicts
-62dB + 13dB = -49dB or better
VOACAP results for WB3ANQ spot
Not enough at 90% reliability!!!
WSPR -28 dB SNR corresponds
to -49 dB SNR for VOACAP
prediction at 0.1 W scaled to 5
mW
Possibly benefitted from some
form of anomalous propagation?
VK6DI
VOCAP result for WB3ANQ spot
Reduce path reliability
to 1% - anomalous!!!
Close enough!
Wait long enough and
even the blind squirrel
gets a nut!
VOACAP run for my VK6DI spot Prediction run for
N6TTO spot by VK6DI with specific Solar weather
WSPR -25 dB SNR corresponds to -62 dB SNR for VOACAP prediction at 0.1 watt scaled to 50 mW
Prediction close against reported spot
VK6DI
SV8CS to California SV8CS spotted on 5/13
with -23 dB SNR running 10mw!
Antenna Moseley Pro-67 at 100‟ – looks like a horizontal dipole at 30m
Corresponds to a prediction of -65 dBW/Hz in VOACAP
Good correlation between prediction and observed results!!!
SV8CS antennas
30m antenna!!
California to Scotland GM4JYB spotted me at -24
dB SNR running 200mW
Very remote & radio quiet location using low Vertical Dipole
-24 dB SNR at 200 mWscales to -61 dBW/Hz in VOACAP
Good correlation between prediction and observed result
GM4JYB
GM4JYB antenna
Very quiet and remote location
Close to the sea and an unobstructed
takeoff
Conclusions - 1 Combining antenna modeling and propagation prediction software
generates results that can be verified against real world observations
General agreement – doesn‟t explain all observed cases but an excellent tool for determining antenna choice, frequency for operation and time of day
Can be a strategic weapon for contest operation IF you make realistic assumptions
Model using your antenna configuration
Assume the average station has a horizontal dipole or vertical
Assume the remote station runs 100w so adjust your expectations about received signal strength in your receiver accordingly
Conclusions - 2
Free software generates good results and enables the learning
curve to be climbed before deciding to jump into
commercial software
For me, I‟ve added EZNEC and PropLab-Pro to my must
have tools – to go with an antenna analyzer and „scope
Provides a basis for experimentation
Fast to try and decide whether to commit to an implementation
Conclusions - 3
I still haven‟t been able to duplicate Larry‟s spot!
VK6DI has moved to Eastern Australia so I guess I‟ll never will!
Chalk up another one to life‟s mysteries!
Always learning, always something new!
WSPR is seriously good FUN!!!!