Hi guys
We, at club station built 80m 4-SQ antenna, but none of us have experience
with phased arrays, therefore several questions, maybe childish, remains
unanswered. Possibly, antenna can work better. Let me explain.
After first radiator erection we measured its impedance and resonance. It
was 70+35j @3,65MHz. Resonance was at 3,36MHz Z=44+0j. We decided NOT cut
off antenna and erect remaining 3 verticals. After that we measured
resonances at the bottom of each vertical. They were about same as with
single element erected: ~42-44 Ohm (!?). Phasing device is built according
well known scheme, TK5EP description http://www.egloff.eu/index.
php?option=com_content&view=article&id=4&Itemid=136&lang=en. Its probably
named Collins phasing. Now goes interesting part: minimum power dissipated
on 50Ohm load is at 3,60MHz, which is almost good for us. And here goes
first question: How target system impedance is determined? is it by minimum
power dumped on 50 Ohm load or somehow measuring radiator impedanses? Its
hard me to believe resonance jumped 240kHz.
Next question is about matching devices at the bottom of radiators. I may
need them for SSB subband or may not need. If I add LC matching devices,
what happens with phases? how does it affect all system work?
Can I measure phasing box output port impedance while keeping all other
ports connected to antennas and one 1/4L 75Ohm cable toward radiator to be
sure matching at this point is acceptable? As much as I understand it has
to be ~100Ohm.
Thank you
--------------------
Vytenis LY2KZ
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