Collapsible Quadrifilar Helix Antenna

Build a collapsible quadrifilar helix antenna and use rtl-sdr to
listen to 137.5 MHz NOAA weather satellites
a workshop by @fbz aka Fabienne Serriere    fabienne@fabienne.us
first presented at BruCON 2012 in Ghent, Belgium
September 27th, 2012
http://2012.brucon.org/index.php/Talks_and_workshops#fbz_-_Hardware_Hacking

Build a collapsible quadrifilar helix antenna for 137.5 MHz NOAA
weather satellites. Use it with an rtl-sdr board, also provided,
(Terratec Cinergy T Stick RC Mk II (PID 0x00d3) with Elonics E4000).
You can be a complete beginner for this workshop. Please bring a
laptop, preferably with gnuradio installed and running (yes this is a
pain, but it won't be covered too much in this workshop). Tools to
build the antenna and materials for the antenna will be provided, an
rtl-sdr board will also be provided. You will walk away with a
collapsible (or fixed) quadrifilar helix antenna and an rtl-sdr stick,
and hopefully a head start at the amazingly cheap way of grabbing
satellite images from space! Available slots: 10. Cost: free as in
beer

cost of antenna materials per antenna (if you want to make another one
yourself): about 10 Euros
plastic piping and various cabling

cost of rtl-sdr Terratec Cinergy T Stick RC Mk II (PID 0x00d3) with
Elonics E4000: 20 Euros
(currently available off the shelf at Saturn in Berlin Alexanderplatz)
http://sdr.osmocom.org/trac/wiki/rtl-sdr

Main mast of antenna: 1m or shorter, minimum probably 630mm, but measure first.

If you want antenna to be collapsible, cut one of the 1m lengths with
wider flange at end exactly in half. you'll have antenna. that will
leave you with an attachment point between the bottom two support
heights.

If you want it to be fully collapsible, consider allowing yourself to
pull smaller pipes out of longer pipes when completed, aka don't glue
it yet, and make the fittings tight.

lengths to cut in skinny pipe (16mm pipe):
3 x 378mm (blue in diagram) (slightly longer, notch should be at 378)
3 x 340mm (yellow gold in diagram) (slightly longer, notch should be at 340)

Cut notches in each end of all six small pipes corresponding to length.

Drill points, leave a bit of room at the top for a cap if you find one
later (a couple of centimeters).

Drill with the 15mm drill through the pipe according to the diagram,
leave extra room between the bottom two pipe supports for cable holes.

Drill four smaller holes underneath each bottom pipe support (between
the sets of holes).

Thread smaller loop through correct holes in bottom of pipe.

Cut longer loop in half. On  one end, B2, twist together the inner,
outer and connect it to the braid of both the second half and the
braid of the feeder cable. Solder together. Mark opposite end with B2.

Solder together the inner feeder to the second half's bottom inner to
the feeder's inner. Wrap exposed areas in electrical tape to prevent
shorts.

Thread the two Y ends of the long loop through the bottom holes.

Solder together at top according to diagram.

One end of short loop S1, both inner and outer should be connected to
inner and outer of B2, and connected to center of B1.

Other end of short loop S2, both inner and outer should be connected
to braid of B1. Use electrical tape and hot glue to isolate and
strengthen.

Feed the cables over the supports, the short supports are for the
short loop, the long supports for the long loop.

Julian, G4ILO's instructions based on Chris van Lint's article:
http://www.g4ilo.com/qfh.html

Chris van Lint's instructions, include 75Ohm cable, but we'll be using 50.
http://is.gd/TN1DEq
http://web.archive.org/web/20090605023132/http://m0nde.co.uk/CVLQFA.htm

wiring diagram of all quad antennas, top:
http://is.gd/QLq2jw
http://www.gregorystrike.com/wp-content/uploads/2010/05/QHA_Wiring.png

kind of too huge to carry home copper based antenna:
http://is.gd/XNKuBQ
http://www.gregorystrike.com/wp-content/uploads/2010/05/P50401741_Rotated1.jpg

with how-to here:
http://is.gd/DI0nXE
http://www.gregorystrike.com/2010/05/16/quadrifilar-helix-antenna-137-mhz/

scientific paper on quadrifilar helix antennas (warning pdf)
http://is.gd/1CGe1o (pdf)
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.emgo.cz%2Fwww_profi_137%2Fpdf%2FRQHAeng.pdf&ei=KdBdUJVGxOm1BoyFgKgP&usg=AFQjCNEuAnbSK4kjVab9o0gnSGZcfEIw6A

many more links on QFA (Quadrifilar Helix Antennas)
http://perso.wanadoo.es/dimoni/ant_qha.htm
http://www.askrlc.co.uk/

http://is.gd/JuXB7U
http://www.poes-weather.com/index.php?limitstart=2&Itemid=1&option=com_content

Double cross antenna (a huge pain to build without pvc pipe cross
pieces, or in future 3d printer):
http://is.gd/4ECMCI
http://www.poes-weather.com/images/stories/station/20%20July%202007%20007.jpg