QFH?

2“QFH?” means “Do you have a quadrifilar helicoidal?”

As of this morning I am “QFH” and ready to receive NOAA weather satellites – in fact, I already have with the antenna indoors and propped against a wall. The resulting image is nothing to write home about but I have no doubt that once placed outside in the clear, the images will be fine.

This whole thing started with the Funcube Dongle Pro+ that I received a few weeks ago. Surfing the web to see what others were doing with this thumb-sized marvel sparked my interest in using it (for now) for this purpose.

I have absolutely no experience building VHF antennas but the online calculator made it into a simple project that cost a total of $6. That’s for the PVC and two wooden dowels that form the antenna’s skeleton. Most people use 1/4″ copper tubimg of even old RG-8 for the actual elements but, being a cheapskate, I just used 12g wire that used to be a dipole.

Following the dimensions given in the calculator led to a finished product that has a 2:1 SWR from 126-144 MHz. The NOAA sats are on ~137 MHz. Not that I’ll be transmitting but I wanted the antenna to be resonant in its required range.

Prior to building the antenna I tested the ability of the FCD+ to receive them using my 80m dipole. At times during a satellite’s pass, the signal was very strong; a few seconds later, no copy at all. This is because the satellites tumble as they pass overhead thus requiring an antenna with right-hand circular polarization like the QFH.

Work schedule (and satellite schedule) permitting, I’ll have decent images in a few days. There are quite a number of these satellites in orbit but only three are currently functioning.

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  2 comments for “QFH?

  1. August 23, 2013 at 4:07 am

    I used to receive wxsats mny years ago using an antenna like the one you built.The problems used to be pager interference, and the IF filters of most receivers being too narrow. The SDR software shouldn’t have that problem. I look forward to seeing some great images

    Julian, G4ILO

    • August 23, 2013 at 6:15 am

      Hi Julian, I saw your write-up when looking for antenna designs and started to build it with RG-58 but the 12g wire was so much easier to work with. I like the ability of SDR#/FCD+ to have such steep “virtual skirts” on whatever bandwidth is dialed in.

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