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!!!!