stacking tribanders

K8DO at K8DO at
Sun Jul 30 14:23:55 EDT 1995

I'm using Elnec to help sort out the bugs in an interleaved 40 / 20
"monobander" stack, with some tribanders, also... The forward stagger idea of
the Force 12 antennas does work... I modeled the 3 el' 20 mounted forward on
the boom of the 3 el' 40, with the reflector of the 20 ahead of the DE of the
40... Elnec shows minimal interaction... Aluminum tube is on order and
construction soon to start...
The tower is 150'... Plan at this time is placing the usual tribanders at 30
/ 90 / 120 and the 40m / 20m 'forward-staggered / interleaved' mono's at 60 /
A couple of issues remain to be solved... 

A)  For the three tribanders... C3 v/s KT's v/s TH's ?   -   ala. this
B)  If I try to run the three tri's and the two mono's on  20 as stack, will
the relative forward stagger of the 20 mono's at 60 / 150 cause destructive
phase differences with tribanders?  I'M working on modeling this to try to
get a feel for the answer.... In fact, I should be doing that right now
instead of writing this... :>)
C)  Also, I have seen opinions here that one does not get as good results
when the antennas in a stack are not identical... That seems logical, yet I
KNOW that identical antennas at differing heights have different complex
impedences and therefore, different  voltage v/s current, phase angles at the
antenna leads, when excited by a common EM wavefront... So, where does that
leave us?  We know that stacking helps in the real world... Are we all
missing a point here on stack phasing that will improve things even more?  We
ASSUME that equal feedline lengths gives the best phasing...   I urge those
of you with stacks to get a scope and compare the phase of the received
signal of 2 antennas at differing heights...  We may find that, like the 4
square arrays, correcting feedline lengths will make a dramatic improvement..
D)  Thirdly, (or whateverly this point is) I strongly suspect that even for
antennas in a perfect vertical plane, the incoming EM wavefront is at an
angle to the vertical and thus the lower antennas are excited later than the
higher antennas - i.e. have a lagging phase angle  - Thus, should each lower
antenna on a stack have a different feedline length?

Questions, questions.... I'm open to any answers....

Cheers ...  Denny        K8DO at AOL.COM

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