This is a quadrifilar helicoidal antenna structure serving as a base for building a 137MHz NOAA satellite reception antenna.
Computations were done using Mr. John Coppens QFH antenna online calculator (thank you very much!) :
Edit 2015-04-11 :
- Added a picture received today with the antenna (no amplifier, only the antenna connected to the SDR RTL2832U dongle :-) )
This antenna is too large to be printed in one shot so I cut it in 8 parts (files QFH137mhz_V2_cut1 - 8 provided).
Note: the antenna is printed upside down (it was easier) so in the end the first part (cut1) will be the top of the antenna
- Print each part one by one in the given order (cut1 to cut8)
- glue parts together (I used epoxy glue), cut2 is glued on top of cut1, cut3 ont top of cut2, ... Note that I put a line of reference along the center cylinder so make sure all parts are alligned (straight line from top to bottom of the center cylinder)
- drill a hole on both side of the cylinder on part 7 in order to insert the smaller loop copper wire
Next step is to add the antenna cable. I used standard 75 Ohm coaxial TV cable because my receiver is a RTL2832U USB dongle (which is designed to be connected to a standard TV antenna).
The cable is inserted inside the center cylinder but you need to drill two holes through the cylinder in cut1 part in order to wind the cable (choke balun). Make sure you have enough cable sticking out the top of the antenna (2 or 3 cm should be sufficient).
Next step is to build the two loops. For this I used copper wire (2mm diameter). Start inserting the wire in the hole at the extremity of one horizontal arm in cut1 part (top of the antenna), then in the corresponding arm in cut2 an so on. At the bottom of the antenna continue with the opposite hole of the same arm and then go up until the top of the antenna and cut the copper wire. First loop is done, do the same procedure for the second loop.
The result should look similar to the picture I posted.
Last step is to solder the wires on top of the antenna. I made a small piece of PCB so it was easier to solder. A detailed picture is available on John Coppens website (picture at the bottom of the page): http://www.jcoppens.com/ant/qfh/adapt.en.php
Another good picture is available from another source:
Should you need more details don't hesitate to comment.