Original 137MHz QFH / QHA constucted by G6KIZ

 

Quadrifilar Helix Antenna for the 137MHz APT weather satellite bandDesign and Construction
Built to the dimensions given in these tall thin QHA pages using 40mm plumbing waste pipe and 8mm microbore tubing.

The tall thin design makes bending the tubes very easy and the hardest part was actually locating some 8mm elbows without paying a fortune in post – most online DIY sites are not geared to small orders and offer courier delivery that costs more than the elbows. I eventually spotted some on eBay.

As can be seen from the picture I mounted the QHA above a turnstile. This may have been a big mistake mechanically as obviously the tube is weakened by the join – something obvious afterwards but which I completely missed in the (lack of) planning stage. It sways around rather alarmingly in the slightest breeze and I really can’t expect it to survive a storm but miracles do happen and maybe it will – time will tell. At least it is pretty lightweight construction and unlikely to do much damage to anything other than itself if and when it comes down.

Performance
Electrically the SWR was virtually 1:1 measured close to the ground. In position it is slightly higher which may be caused by the actual height, cable length which is a bit less after mounting, or possibly it got a whack during installation. Whatever the cause it still seems to perform very well. Watching the R2ZX during a pass mostly the QHA is used by the diversity up to around 30 degrees elevation above which the turnstile gets most use. This is exactly what I expected.

Conclusion
Producing the QFH /QHA was worthwhile as the pictures certainly appear to be better. If it does all come tumbling down I’ll have to decide whether to rebuild it or stick with just the turnstile which was cheaper and easier to build and produced results only slightly down on the QHA.

I’m not paranoid they really are after me.


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