Topband: ??? from ON4UN Book

[Bill Tippett]

N1EU wrote:

>Would appreciate it if others could confirm that there is an error on page 
>10-8 (new edition), third paragraph from top.  Shouldn't it say "Bill used 
>what he calls a squashed delta loop on 80 meters", not "160 meters"???

Hi Barry!

        My delta loop was indeed for 160 meters.  It was approximately
240' on the base with each side about 150'.  This forms a triangle that
is 90' high.  As I recall, the impedance at the feedpoint was around 120
ohms.  I fed the loop in the corner via 1/4 wave of 75 ohm coax
which yielded almost a perfect match to 50 ohms.  The loop does NOT have
to be fed 1/4 wave from the top and modeling shows both the impedance
and pattern are not affected by feeding it in the corner which is much
more convenient.  Modeling also shows the "squashed" delta actually 
has about 1 dB more gain than an equilateral delta, primarily due to the
two vertical sides having more separation.

        Assuming the base of the loop is 6' high, you would need a 
support 96' high to suspend the apex.  However you can pull the base
away from the support so that shorter supports can be used.  This
also enhances the gain slightly in the direction you move the base
at the expense of reduced gain on the "backside".  If you pulled the
base out 30', you could use a support about 90' high.  I believe 
W3BGN uses a similar antenna with very good results on 160.  I am not
sure about pulling the base out too much farther since you might begin
to lose the low angle effectiveness of the antenna but you might
take a look at EZNEC to see what happens.

        I was very happy using delta loops for a couple of years but
finally went to a shunt fed vertical because of difficulty in working
stations in the loop's nulls to the side.  Hope this helps!

                                        73,  Bill  W4ZV

P.S.  The actual loop I finally evolved to was opened at the top and
suspended from 150' at my first NC QTH and at 180' from my present 
QTH.  An opened loop offers increased gain over a closed loop but
does not significantly affect the impedance.  


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