Building a Quadrifilar Helix (QFH) Antenna
With a QFH antenna you can pick up weather satellite radio transmissions and convert them to images on a modern PC.
My old double-dipole antenna did quite a good job but you still had to move it around to ensure you didn't lose the signal as the satellites fly overhead.
I'd seen these Quadrifilar Helix Antennas (QFH or QHA) before and was always intimidated by the complex looking architecture, compared to a dipole antenna which is essentially just 2 pipes arranged next to each other.
One weekend in March 2014 I decided it was QFH-building weekend, so headed down to B&Q, my local hardware store, and bought what I needed...
- 2m x 32mm PVC pipe (for the stand)
- 2m x 21.5mm PVC pipe (for the horizontal arms)
- A pack of cable ties, just to keep things neat
- 15+ metres of 50 ohm coax cable.
- 10 metres, single core earth cable (green & yellow), 10mm2 - this was used for the actual antenna elements.
I then headed to Maplin, thankfully next door to B&Q to get a BNC plug, and some ferrit beads to try and prevent interference between the antenna and my scanner.
Following a few guides online I managed to construct something vaguely resembling the target antenna.
I'm not going to repeat what others have already done, a quick Google will find a hand-full of guides, but what I learned along the way, was, don't worry so much about the exact dimensions. Just build it and use it, and you'll soon be amazed at how much better a QFH antenna works than standard dipoles... for satellite transmission anyway!
When trying it out for the first time I was amazed, perfect quality signal, no drop in strength, even by propping the QFH antenna in the corner of my lounge.