Hi Rich,
> All 5 driven elements are tied together at a supplied 2:1 balun. With
> this set up only one feed line is required. The quad worked very well
> except on 10 meters. It did not work on 10 meters because (my opinion
> only no scientific back up) of two things. First, I think it would have
> worked better on 10 if it had a seperate feed line. Second I don't think
> the spacing was correct. K5ESW did some modeling and found that the
> spacing on 10 was a problem.
It was not the spacing that seemed to cause the 10 meter problem. My modeling
work
showed strong interaction with the 20 meter loop and 12 meter loop when using a
single
feedline and driving the quad on 10 meters. I modelled various changes trying
to keep a
common feedline, but I did not come up with a combination that was acceptable.
There
may be one, but I did not find it.
I used the original Lightning Bolt quad spacing but changed some of the loop
lengths and
used a separate feed for each band. Instead of a separate coax from each driven
element
to the shack, I used a switchbox mounted on the boom. I ran 1/4 wavelengths of
70 ohm
coax from each loop to the switchbox and 50 ohm coax from the switchbox to the
shack.
This gave me a feedline impedance of about 110 ohms at the loops.
The model also showed that when using 1/4 wavelength lines to the switchbox, it
was
important to have the switchbox leave the lines not in use (undriven)
open-circuited as
opposed to shorted. Open 1/4 wavelength lines give the appearance of a short at
the
undriven loops at their resonant frequency. If the 1/4 wavelength lines were
shorted, the
undriven loops appear as open loops, and there were some strong interactions. I
actually
included the 1/4 wavelength feedlines in the model, but you could see the same
affect by
running a model with the unused loops as either closed or open circuits.
I modelled a few random length feedlines, and it did not show strong
interactions whether
the undriven feedlines were left open or shorted.
If you want minimum interraction, my recomendation for a 2 element 5 band quad
is to use
a separate feedline for each band.
73,
K5ESW
Paul
Paul.Ferguson@pobox.com
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