An NEC4 analysis shows a 5+5 20m stack beats a dipole at the same max
height (125') in absolute gain by 10db (7.6dbi to 17.6dbi). This 5+5 owa
is <1.25:1 swr band edge to edge. The dipole has several -1 to -3db
high angle lobes to pick up local QRM/QRN so the stack has another big
advantage for working DX. There are many bigger stacks out there that
do better.
Re the other assertions, you may want to check out what designers using
computer analysis have produced for very good multiband interlaced
antenna designs. These interlaced designs tend to be on shorter booms
because it is easier to do, and that is where the market is. Putting 5
bands on one 48' boom has been done, but it is pretty complex.
Grant KZ1W
On 2/19/2015 11:05 PM, Chuck Smallhouse wrote:
"Since the 70s, at least a dozen times we have helped swap a Mosely
TA-33 jr to
something else, usually a Hy-gain 204BA. The difference on 20m is the
usual 10 db".
You really must have drunk a lot of the CC Kool Aid. There is no HF
yagi antenna that has anywhere close to 10 dBD gain, let alone that
difference over another ! Even a stacked monobander system doesn't
come close to 10 dBD gain .
In my opinion, no multiband yagi has anywhere close to optimum gain,
they are all compromises. To meet the current needs of SS xmtrs and
PAs (no manually tune pi networks) they are designed to be broad band
and thus compromise gain. The more elements (more bands) the
greater the compromise.
The tunable SteppIR that supposedly can be optimized at all
frequencies across a band, might be better, even though the element
spacing remains the same for all bands and frequencies. However
monoband yagis, with good gain, can be designed with element spacing
of < 0.1 WL to > 0.3 WL. I assume that SteppIR's S/W takes this into
account, therefor essentially making them a muti-band set of monoband
yagis.
No I don't have one - just a fairly new design, broadband tribander.
Chuck, W7CS
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