Trials, errors and construction of a crossed

Satellite Weather Pictures First-Hand, Part 1
How to receive NOAA weather satellites
using a home-made turnstile antenna
Inspired by an article in the German
magazine “Funkamateur” (issue 7/05,
p. 674), I wanted to try capturing
pictures from weather satellites as
seen on TV.
The following article describes my
experiences; however, I have omitted
details that can be found elsewhere. The
operation of the PC software has been
described in the above article and can be
looked up in the software “Help” files.
The terms following in italics can be
found via “Google”. Only the antenna
used is described in detail, as I found
only little information for home-making
one.
What is the NOAA?
It is an American Authority with various
functions (see wikipedia.org) which
operates, among other things, several
own weather satellites. These are
transmitting in the 137 MHz band and
can be received legally and cost-free by
everyone.
Reception uses PC sound card and
software
The receiver should be capable of
receiving 137 MHz and be set to Narrow
FM. The audio signal is fed into a PC
sound card. The PC runs the software
WxToImg which shows not only when
and on what frequency a satellite can be
heard, it also starts and ends the
recording automatically.
Live reception of an NOAA Satellite using
a Yaesu VX-5 and WXToImg
The pictures received can subsequently be edited and improved, e.g. by false colour
display. The basic version of WxToImg is freeware. You can purchase several improved
versions which promise more options and a better picture quality.
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Another very useful software is WXTrack. It shows the flight curves of all official satellites
(not only weather sats), also of the International Space Station ISS. This has enabled me to
copy the ham traffic coming over the ISS repeater when it flew over my location.
Screen shot: WXTrack displays NOAA 15 over the radio horizon of Berlin (+).
The window in the back is WxToImg, building the picture currently received by NOAA 15.
The NOAA sats are orbiting the Earth with relatively high speed from South to North or vice
versa. They are rising over the horizon, flying over your location in about 10 minutes, then
descending on the other side of your horizon. They continuously transmit a multi-channel
picture (infrared and daylight views with up to four sensors) which builds up line by line on
the screen.
First Reception Attempts
With my large 2 m/70 cm vertical antenna (Diamond X-300) I could hear the sat’s audio
signal, but the picture was garbled.
May be a directional antenna with position tracking would help?
WxToImg and WXTrack both display the sat’s elevation (the angle over ground when
looking at it from your location) and azimuth (position on a 360 degree compass rose).
Beforehand, you need to download the Kepler data from the internet. This way you always
know not only when the sat will show up and disappear, you can also tell its current position
in the sky.
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This helps a lot to evaluate the reception (e.g. the signal gets weaker when the sat
disappears behind a high-rised building) and for tracking the sat with a directional antenna.
Both programs can do this fully automatic if you have the relevant equipment –
unfortunately, azimuth/elevation rotors and related computer interfaces are very expensive.
I therefore tried a “manual” solution.
Manual Satellite Tracking
For manual tracking I used a small
compass and an enlarged
compass scale printed on paper as
well as a 90 degrees angle scale.
With this simple equipment I
manually tracked the satellites with
a 2m directional antenna while
watching the elevation and azimuth
display, enlarged by the Windows
Screen Loupe.
This resulted in a slightly better
signal strength but still delivered
poor pictures.
You Do Need an Antenna with
Circular Polarization!
The satellite transmission
antennas have circular
polarization, so I built myself a
crossed dipole antenna, also
known as turnstile antenna.
I found instructions under
www.dl7awl.de/dipol.htm.
I modified the suggested design to
be able to use only materials I had
in stock.
I mounted the dipole ends inside the junction box with small clamps onto a piece of wood.
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The antenna pole is a very old PVC tube with 40 mm diameter. Inside the pipe is the
transformation line going downwards from the junction box and a PL connector for the
regular coax cable leading to the receiver. This way everything was easily made rain safe
as well.
Measuring the antenna with an analyzer showed an SWR < 1:1.4 in the entire 137 MHz
range.
The junction box is laying loose on top of the pipe which facilitates stowing and
transportation of the antenna (R. H. picture).
The reflector is mounted 80 cm underneath the crossed dipole.
You may want to drill holes at several heights into the PVC pipe to optimize reception by
trying different distances between reflector and dipole.
The following page shows a couple of details.
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If you drill the holes
in the junction box
smaller than the
diameter of the
dipole elements,
the soft PVC
material will provide
for some rain
sealing.
To protect from
condensation
water, I drilled
another two holes
into the bottom,
small enough to
prevent insects
from nesting inside
;-)
Detail of the
reflector. Both
metal bars are held
together using two
cable ties, tied
crosswise. To
ensure the reflector
is horizontally, you
have to carefully
balance the free
hanging metal bar
;-)
Of course, you
could fix it to the
pipe using more
cable ties, but then
the antenna will no
longer fold for
storage…
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And now some of the NOAA satellite pictures I received with this antenna:
If desired, WxToImg puts a map overlay over the picture received. The yellow cross
indicates my location.
This picture was taken in the evening. You can clearly see the shadows of some cloud
“towers” over Germany, generated by the sun dawning in the West.
The cloud swirl over the Mediterranean Sea was surely not a tornado…
The best picture quality can only be achieved with certain scanner models (listed on the
WxToImg web site) or with specialized weather satellite receivers, since the sat signal is up
to 30 kHz wide.
With common ham equipment, like my IC-706 and VX-5, having only 10 to 15 kHz
bandwidth, you have to live with less contrast in the picture. Switching to WFM does not
help. The author of WxToImg promises that the upgraded version (approx. 50 Euros)
delivers a better picture with “narrow banded” receivers.
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The bar code on the border is telemetry data.
False colour display showing interesting cloud formations. Looks like it was very
windy over the Irish Sea, as the clouds appear so stretched.
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The horizontal picture disturbances were generated by ground reflections and deletions of
the radio waves. Since every sat pass is on a different flight curve, this can always happen.
The misalignment between map and actual land borders can be corrected using the
WxToImg menu item “Move Map Overlay”.
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As is often the case in
February-March, Germany is
almost completely covered by
clouds – whereas in France
and Italy, the sun is shining…
Fluffy clouds over the Irish
Sea.
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Depending on the flight curve of the sats, the high-rised buildings North West of my location
in 100 and 200 m distance disturb reception when the satellite is declining in the North.
Future Plans
When the weather turns better in Spring, I will try mobile reception from an elevated
location. I hope for pictures with less distortion. This is covered in part 2.
Conclusion
Capturing weather sats is fun, even if you are not a meteorologist!
It fascinates me when a satellite, announced exactly to the minute by the computer, shows
up on a normally empty frequency, with me being able to decipher the strange audio
signals (it sounds like a metallic, high-pitched “singing” with hectic “tic-tocs”. These are
the telemetry signals showing as barcode on the picture border.)
I have learnt a lot about satellites, built an interesting antenna and enlarged my radio
knowledge. Beforehand, it did not know what azimuth and elevation mean – now I can point
with the finger to the position up in the sky where the satellite is just now!
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Even if you do not have a ham radio license, you can capture satellites with your radio
scanner – the software needed is free on the internet!
Enjoy!
Disclaimer: You are welcome to do and try what I did, but please understand that you will
do so at your own risk. Thanks!
I appreciate your comments and questions. Please send an e-mail to <mycallsign> <at>
darc.de (this spelling of my e-mail address shall protect me from spam bots).
73,
Andy, DL4AND
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