[TowerTalk] Mast size for stacking

Jim Jarvis jimjarvis at verizon.net
Tue Aug 15 04:20:37 EDT 2006

N5XZ wrote:
 I am planning to install a 4-el SteppIR at 70 ft and possibly another HF
> beam above it in the future. One plan is to install a 10-Meter monobander
> in a few years when the spots come back. Another is to install a 2 or 3 el
> 40-meter monobander.
> 1. How much benefit would I get mounting the 10-meter mono above the
> SteppIR on the same mast and how far should I space it if I do it.
> 2. What size and material mast should I use if I mount a 40-meter beam
> above the SteppIR? (Material / length / wall thickness, etc)


Multiple questions here.

1) If you invest in a 4 el steppIR, you would be hard pressed to
improve on it much with the monobander.  Not that you wouldn't..
for an equal length boom, the monobander should give more fwd gain.
but on 10, when the band is open, I'm not sure you'd notice the
difference in performance.  With a 3 el steppIR, you might see the
difference between it, and a long boom  6 or 8 element 10m monobander.
But the longer boom would have a tighter forward lobe...not always what you
want on 10.

2)  Stacking.  You are unlikely to see more than 1dB added gain from
the complexity of a bip-bop stack at 28MHz.  What it will give you is
angle control.  I would avoid the problem of stacking dissimilar antennas,
and put my money into motorizing the tower, so you could put the steppIR
at the best height for the band in use/prevailing condx.

    Without a doubt, during the sunspot peak, 10m gets very high angle at
mid-day.  Vertical angle control is a benefit...but so is having a low 10m
beam...say 20-30'.  We used one to great benefit at W3GM's contest stn, when
the array at 100' wasn't effective.

3)  I like 40m, so my stacking choice would be a 2 el 40 above the steppIR.
But I
haven't explored their 40m add-on yet.  Ease of maintenance is a factor
shouldn't be overlooked, when you go above the top of the tower.

jimjarvis at ieee.org

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