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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