Pages: [1]   Go Down

Author Topic: Stacking dissimilar yagis  (Read 380 times)

K3GM

  • Member
  • Posts: 2646
Stacking dissimilar yagis
« on: October 21, 2021, 03:36:44 PM »

When considering a stack of dissimilar VHF and UHF yagis, invariably, research will find that if a 6m yagi is involved in the stack, it will always goes on the bottom.  My question does not pertain to stacking distance, but stacking order.  Is the location of the 6m yagi on the bottom for mechanical, or for electrical reasons?
6m is my bread and butter band.  It's the band that garners the most contacts and grids in a contest.  But with my modest tower, limited in height, holding 5 bands, 6m, 2m, and 70cm yagis, a 23cm looper, with a 1.25m FM vertical on top of the mast, I'd like to place the 6m antenna at the top of the stack to get it as high as possible.  But I'm concerned that I would be violating an unforeseen electrical law like beam pattern tilt or the 6m yagi acting as a ground plane of sorts to the other 3 bands.  Any opinions?
« Last Edit: October 21, 2021, 03:40:50 PM by K3GM »
Logged

AA4PB

  • Member
  • Posts: 15504
Re: Stacking dissimilar yagis
« Reply #1 on: October 21, 2021, 04:01:29 PM »

I think it's mostly a mechanical issue. If the larger, heavier antenna is located closer to the rotor then there will be less load on the mast and rotor. It should work fine at the top as long as you maintain proper spacing and the mast and rotor can handle the weight and wind load at the top.
Logged
Bob  AA4PB
Garrisonville, VA

W7CXC

  • Member
  • Posts: 336
Re: Stacking dissimilar yagis
« Reply #2 on: October 21, 2021, 04:06:49 PM »

AA4PB +1 David
Logged

K0UA

  • Member
  • Posts: 9589
Re: Stacking dissimilar yagis
« Reply #3 on: October 22, 2021, 07:06:10 AM »

I don't understand why you would want the 6 meter antenna as high as possible. The 6 meter antenna will not profit from the additional height, but the high vhf and uhf antennas will. At least in my opinion. Perhaps others would care to comment, and perhaps I could learn something, but I sure would not put the 6 meter antenna on top, as I don't think you will gain anything by doing so. Assuming you are working Es not ground wave with your 6 meter antenna. Or hope of hopes, maybe someday F2 with it, I don't think you gain a thing by going over 1/2 wavelength over the ground. And I certainly don't think you are going to gain anything by using one end of your mast over the other, in other words the extra 10 foot or whatever the length of your mast is. All you will be doing is putting a higher weight and wind load up where you don't need it. So a no vote for putting the 6 meter antenna on top here.
Logged
73  James K0UA

AA4PB

  • Member
  • Posts: 15504
Re: Stacking dissimilar yagis
« Reply #4 on: October 22, 2021, 09:30:39 AM »

James, I think you are correct, depending on the height of the tower and whether you are working Es. If the tower is say, 30 feet or if you are interested in local nets with stations in the 50 mile or so range then the top location may improve performance.
Logged
Bob  AA4PB
Garrisonville, VA

VE6MB

  • Member
  • Posts: 59
Re: Stacking dissimilar yagis
« Reply #5 on: October 22, 2021, 02:06:18 PM »

If we are talking only two bands (two yagis)...won't make much difference. But if we are saying three bands/yagis or more...then having the lowest band (with the largest aperture) at the top will leave you more space on the mast for spacing the rest of the yagis with their various apertures and less interference between one another. A good document to have a look at is: http://www.jdunman.com/ww/AmateurRadio/Antennas/Stacking.htm (look at figure 7 or figure 8 ).

73, Valentino, VE6MB


I don't understand why you would want the 6 meter antenna as high as possible. The 6 meter antenna will not profit from the additional height, but the high vhf and uhf antennas will. At least in my opinion. Perhaps others would care to comment, and perhaps I could learn something, but I sure would not put the 6 meter antenna on top, as I don't think you will gain anything by doing so.
« Last Edit: October 22, 2021, 02:11:59 PM by VE6MB »
Logged

K0UA

  • Member
  • Posts: 9589
Re: Stacking dissimilar yagis
« Reply #6 on: October 22, 2021, 02:48:09 PM »

I saved that bookmark about stacking. Tnx for posting. And in the illustrations that showed a 6 meter beam, of course they put it on the bottom of the stack.
Logged
73  James K0UA

K3GM

  • Member
  • Posts: 2646
Re: Stacking dissimilar yagis
« Reply #7 on: October 22, 2021, 07:53:58 PM »

If we are talking only two bands (two yagis)...won't make much difference. But if we are saying three bands/yagis or more...then having the lowest band (with the largest aperture) at the top will leave you more space on the mast for spacing the rest of the yagis with their various apertures and less interference between one another. A good document to have a look at is: http://www.jdunman.com/ww/AmateurRadio/Antennas/Stacking.htm (look at figure 7 or figure 8 ).

73, Valentino, VE6MB
I have been using this paper in my planning.  The author Dave Olean, K1WHS is an excellent source.  But the aperture is formed above the boom, so if placing the 6m yagi on top, won't the aperture then affect the antennas below?

I don't understand why you would want the 6 meter antenna as high as possible. The 6 meter antenna will not profit from the additional height, but the high vhf and uhf antennas will. At least in my opinion. Perhaps others would care to comment, and perhaps I could learn something, but I sure would not put the 6 meter antenna on top, as I don't think you will gain anything by doing so.
James, what you raised is something I failed to consider.  The tower is 30' tall with 10' of mast above the thrust bearing.  The 5 element, 6m yagi while not a monster, does use a 20' boom.  All antennas are used for weak signal DX.   I have the 70cm and 23cm antennas spread apart on a very wide H frame in order to squeeze them onto the 10' mast.   This leaves enough space on the mast to mount a 2m K1FO yagi.  I will think about what you're saying and perhaps rethink my stacking arrangement as nothing is on the mast as of yet.  Thanks to all for your input.
« Last Edit: October 22, 2021, 08:06:56 PM by K3GM »
Logged
Pages: [1]   Go Up