VHF+ Vertical Antenna Stacking: More than 3 dB gain? Yes!
by Mike Waters, W0BTU
I have used both single and stacked
beams, ten meter Yagis and two meter Quagis. Every time I stacked two
together the logical choice was
VERTICAL, one over the other. Vertical stacking of VHF and UHF antennas
is nearly always more
desirable than horizontal (side-by-side) stacking, and the apparent gain when stacking them
vertically is more than the 3
dB than one would expect. Here's why that
Horizontal Stacking (Both antennas side-by-side)
(Not many hams
run more than one antenna, and those that do usually stack them
Horizontal stacking will increase the gain by about 3
dB, and narrow the beamwidth. The radiation angle with respect to the
horizon will be the same as a single antenna (that is, too high). Both
of these conditions are usually undesirable.
The radiation pattern of either a single beam or two beams stacked
horizontally (side-by-side) has a similar elevation angle: in either
case, the radiation angle is too high. And as a result of that high
radiation angle, a good portion of your signal is simply wasted by
beaming it way too high. Way over everyone's antennas, and into outer
Another thing: you had better be
pointed nearly at the distant, weak
station you are trying to communicate with. Since the pattern width is
so much narrower with horizontal stacking, you may not hear other weak
stations that you are not pointed at. And neither might you hear such
stations calling CQ, nor would as many stations hear YOU call CQ.
That's not all. Nothing changes as far as the received elevation
concerned. That means that we're also listening to an area
higher than the horizon (i.e. towards outer space) as well as
transmitting our valuable RF power there as well. That's also too high;
also way over everyone's antennas, and into outer space.
Why would we want to do that? The goal of erecting antennas is to
effectively communicate with other hams here on planet Earth, not the
moon, not on orbiting objects, nor space aliens. At least that's my
goal here. And if it's yours too, allow me to explain why you should
absolutely, always, stack your beams vertically and NOT horizontally.
But perhaps the most compelling reason for not stacking them
horizontally is that you are not going to solve the too-high radiation
problem. You're still going to radiate to, and listen from, well above
the horizon. There are no other hams there, my friend.
Vertical Stacking (One antenna over another other)
will also increase the gain by about 3 dB. However...
A very marked (read: spectacular) improvement comes with properly
stacking similar antennas one over the other. Gain from a stacked
pair of antennas tends to average well above the 3 dB that theory would
indicate, directly resulting from the lowering of the radiation
angle that comes from such vertical stacking.
Commercial FM and TV broadcast stations
have realized the amazing
advantages of vertical stacking (vertically stacked arrays of low-gain
omnidirectional antennas) and the resultant low angle of radiation for
years. Without exception, they stack them vertically, not horizontally.
That's what it takes. Of course, commercial stations are not interested
in point-to-point operations like hams are.
Pros: Cons: [incomplete]
Pros: Cons: [incomplete]
Don't let ANYONE convince you that if you add another identical antenna
over another one that you have now, that you --and the other stations
you are communicating with-- are only going to see a mere 3 dB of gain!
Unless you have an unusual problem where:
1. There are many close-by hams on the same band QRMing you, or
2. You have an unusual need to reject local QRN noise*
there is little reason for stacking two beams horizontally
(side-by-side) in lieu of vertically (one over the other).
So, unless you have a compelling reason to, stack your two antennas
vertically instead of horizontally!
I stacked my two meter Quagis only 8' apart. Stacking them further
apart may have increased the gain a little, but I don't know what would
have happened to the pattern. The way it worked at that spacing was so
amazing, I don't see how it could have been improved by raising the top
antenna (and thereby the distance between them).
* I had a lot of power line noise at the time I had that amazing
vertically-stacked two-Quagi array. I always wondered how a 4x4 array
would have worked at that QTH. The radiation angle should have been
just as low as 2 over 2, but there would have been disadvantages from
the narrower beamwidth.
My desire is to build a larger vertical array of Quagis, 8 or 16
high, for terrestrial DXing on the low end of two meters.
- The Radio Amateur's VHF Manual, 3rd edition, 2nd printing,
ARRL, p. 184, 198, 199. Time and again, that book speaks of amazing,
unbelievable results from stacking two antennas vertically, and that
book was the primary motivator for me building this array. And so help
me, I was NOT disappointed from following the advice in that book!
On p.199: Is 4x4 worse than
that (read: a
dive, a step backwards)? Seems like that's what's being said; does that
raise the radiation angle?). If so, would a 2 x 8 be better? (2 wide, 4
high). I can't say, I haven't seen a model. Have you?
April 1977, p. 11, The VHF Quagi,
[for 144 and 220 MHz] by Wayne Overbeck, K6YNB (Now N6NB)
- QST, February 1978, p.
20, The Long Boom Quagi, [for
432 MHz] by Wayne Overbeck
- QST, August 1981. Quagi
design for 1296 MHz, by Wayne Overbeck
- Wayne Overbeck's Quagi page, http://commfaculty.fullerton.edu/woverbeck/quagi.htm.
The QST articles can be read here. (Dr. Overbeck's main page is www.n6nb.com.)
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Comtech Research LLC. All Rights Reserved.
Document created January 2, 2011 - Last Edited January 12, 2011