[amsat-bb] Re: QFHA for SO-50... polarization issue ???

Ing. Pavel Milanes Costa pavel at conas.cu
Mon Feb 18 12:29:01 PST 2013

Thanks to all for the reply to this thread...

Conclusion is that I need RHCP & LHCP switchable antennas...

And my antenna is working good... but I'm reading an article Art send me 
to improve my knowledge about QFHA...

73 and Thanks to all.

El 16/02/13 23:21, Ing. Pavel Milanes Costa escribió:
> This weekend I tested a Quadrifiliar Helicoidal Antenna for 70cm (LHCP)
> I designed it by the online calculations of jcoppens on the internet...
> It is a 1/2 turn and 1 lambda, about 5 meters of elevation with ~25 cm 
> of RG-58U (a section of it is coiled to form a balum) and then ~15 
> meters of A.H. LDF4-50A down to the shack directly to the radio, of 
> course BNC to N adapter on the antenna and N to PL259 on the radio 
> side... It's at mast top.
> Results are good... In passes of over 20 degrees (almost the real 
> horizon here) I have a good copy, until... TCA, in which I lost the 
> signal completely...
> TCA = Time of Closest Approach.
> In northbound passes (I've not tested it in southbound) it work as I 
> just said...
> I have been reading and investigating this strange issue and I think 
> it is due to polarization...
> I had read that SO-50 is linear polarized on 2m AND 70cm with aprox 45 
> degrees each other...
> Then Linear to LHCP in the worst case is 3dB loss (half power) but 
> consistent over the entire pass... or have SO-50 some 
> circular/elliptical component in it's signals that renders useless the 
> antenna after TCA? spin maybe?
> There is any chapter of the book I missed or other variable(s) that I 
> have not taking into account here?
> Any comment, link or other kinds of help are welcomed..
> 73 de CO7WT.
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