Stacking Distance Qusetion
 

Hi group... Need some input.

I need to stack two 432mhz quads, not in the traditional vertical plane,
but horizontal. This brings me to two questions... (1) What distance
apart? 1/2 wave length or 1 wave length or ?? (2) Do I need to make
that measurement from boom center line to boom center line OR would it
be end of element to end of element?

Thanks & 73,

Steve
ab5mm

assuming they are being fed in phase and are polarized the same way they
should work best at an odd multiple of 1/2 wave apart... measured boom to
boom. of course at 70cm a 1/2 wave spacing is only 35cm, which is pretty
close and will probably result in unwanted interaction between them. i
would go for at least 3/2 or 5/2 wave spacing... 3/2 spacing is only about
1m which is very workable even in a small space and would be reasonable for
fairly short quads. if they are long ones you may want to go for 5/2 or
even wider spacing. one kind of generic rule of thumb is that you want them
at least as far apart as their boom length..

one other thing, this is not an odd application. it is fairly common to see
horizontal stacking of yagis for vhf and uhf. cushcraft used to sell a pair
of 2m yagis with a cross member and phasing line. many big gun uhf stations
will stack 4x70cm yagis in a square with an H shaped framework.


"ab5mm" wrote in message
...
Hi group... Need some input.

I need to stack two 432mhz quads, not in the traditional vertical plane,
but horizontal. This brings me to two questions... (1) What distance
apart? 1/2 wave length or 1 wave length or ?? (2) Do I need to make
that measurement from boom center line to boom center line OR would it
be end of element to end of element?

Thanks & 73,

Steve
ab5mm

Here is a chart of what the EME'rs are doing for spacing on 2m. Scale
by exactly 3 for 432 for your boomlength.

http://www.vhfdx.net/VE7BQH.html

And here is the DL6WU stacking formula -

--------------------------------------
DL6WU Stacking Formula for Long Yagis

D = W / (2 * sin(B/2))

* D = stacking distance, vertical or horizontal
* W = wavelength, in same units as D
* B = beamwidth between -3dB points.
Use vertical beamwidth for vertical stacking (as above);
use horizontal beamwidth for horizontal stacking.
---------------------------------------

Or you can do it using YO, EZNEC, etc., and increase the spacing until
the first sidelobe is minimized, and the next stacking distance step
makes it larger. I think that's at 13dB down, but I could be wrong,
17dB also sounds correct. ;)

tom
K0TAR

ab5mm wrote:
Hi group... Need some input.

I need to stack two 432mhz quads, not in the traditional vertical plane,
but horizontal. This brings me to two questions... (1) What distance
apart? 1/2 wave length or 1 wave length or ?? (2) Do I need to make
that measurement from boom center line to boom center line OR would it
be end of element to end of element?

Thanks & 73,

Steve
ab5mm

How big are the antennas? The pattern can get pretty sharp and hard to nail on
the station you're trying to peak. No doubt you'll be loud once you're there,
but the wind may blow you off track.

jw
K9RZZ

I need to stack two 432mhz quads, not in the traditional vertical plane,
but horizontal. This brings me to two questions... (1) What distance
apart? 1/2 wave length or 1 wave length or ?? (2) Do I need to make
that measurement from boom center line to boom center line OR would it
be end of element to end of element?

Another one of the all depends questions. If you want a clean patern it is
one spacing, maximum gain is another.
Forget stacking quads at 432 and go with a longer length yagi if you want
the maximum gain.
Quads are good for maybe 6 meers and lower. By the time you get to 2 meters
it is beter to go with a long yagi as the aditional gain of quads start to
fall off compaired to yagies of the same boom length.

I verified that just about 13 dB down on the first sidelobe gives you
the best pattern, and is about .2 down from highest gain.

tom
K0TAR

Tom Ring wrote:




Or you can do it using YO, EZNEC, etc., and increase the spacing until
the first sidelobe is minimized, and the next stacking distance step
makes it larger. I think that's at 13dB down, but I could be wrong,
17dB also sounds correct. ;)

tom
K0TAR