VHF+ Vertical Antenna Stacking: More than 3 dB gain? Yes!

by Mike Waters, W0BTU
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I have used both single and stacked beams, ten meter Yagis and two meter Quagis. Every time I stacked two of them 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 is so.


Horizontal Stacking (Both antennas side-by-side)

(Not many hams run more than one antenna, and those that do usually stack them horizontally.)

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 space.
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 pattern is 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)

 This 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.


Summary

Horizontal stacking
Pros:  Cons: [incomplete]
Vertical stacking
Pros: Cons: [incomplete]
Experiences          [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!


Additional thoughts 

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 antennas high, for terrestrial DXing on the low end of two meters.

References

  1. The Radio Amateur's VHF Manual, 3rd edition, 2nd printing, (c) 1972 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?
  2. http://www.w8ji.com/stacking_broadside_collinear.htm
  3. QST, April 1977, p. 11, The VHF Quagi, [for 144 and 220 MHz] by Wayne Overbeck, K6YNB (Now N6NB)
  4. QST, February 1978, p. 20, The Long Boom Quagi, [for 432 MHz] by Wayne Overbeck
  5. QST, August 1981. Quagi design for 1296 MHz, by Wayne Overbeck
  6. 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.)
  7. http://www.directivesystems.com/lva.htm
  8. http://www.mydarc.de/dk7zb/Stacking/stacking.htm



COMMENTS ON THIS ARTICLE ARE WELCOME, either at http://www.eham.net/ehamforum/smf/index.php/topic,72780.0.html or http://forums.qrz.com/showthread.php?t=279928.

EZNEC .ez files either proving or disproving the above can either be sent to mikewate (at) gmail [dot] com, or posted as .zip and .gif files on the above forums.

 

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Document created January 2, 2011 - Last Edited January 12, 2011

 

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