Hello Johan,
I'm copying the reflector in case we both might get some insights about
the quad antenna type based on two wavelength long elements.
By coincidence lately I've been time modeling
bisquare loops and two element "XQ quads" as you call them. EZNEC and NEC2
predict significantly more gain than for a conventional quad. For the models
I've been working with so far the bandwidth does seem significantly smaller
than that of a corresponding quad. The feedline impedance is, in a word,
"wild", with quite high R and large X values as frequency is changed. Also the
front to back ratio varies greatly with relatively small changes in frequency.
However this is very "early days" for me and I hope some of this bad behavior
will be resolved when I've worked out the important parameters using NEC2. I've
found the perfect off-hours use for my 4 processor, 200mhz Pentium Pro Unix
machine at work :-)
But at this point I'd describe a 2 element bisquare array as the most
unstable antenna I've ever done modeling experiments with. It reduces my
enthusiasm for building one :-) But if I'd properly modeled a Lazy-H I might
not have built one of those and I had great success with that design :-)
For the 10m band, 2 element antenna I was modeling last night, freespace
gain was around 9.5dbi with about 19dbi front to back ratio and 60 degrees of
azimuthal beamwidth. Over medium ground with the top wires at 60 feet the
gain was 15.2dbi with a 9 degree launch angle. This is about 3db better than a
2 element conventional quad. The feedpoint impedance of this antenna was
hugely reactive, e.g. 13000+j2000 to 500-j5000 across the range from 28.3 to
28.8mhz. It would take quite a collection of transmission line transformers
and stubs and what not to match this range, heh? But it's too early for me to
tell what it's bandwidth will be after (if) I get everything sorted out. The
2:1 SWR bandwidth of the single resonant bisquare element I based this model
on was 400hz, however.
What is "MGS"? Is this a vendor in the USA?
Regards,
Pete
KS4XG
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|