Stacking beams
 

Hi, i am going in a VHF/UHF contest this weekend and have a question about
stacking beams.
We will have a pole approx 15-20ft long and want to stack the following
antennas,

1x20 element UHF yagi
1x10 element 2 Metre Yagi
1x5 element 6 Metre Yagi.

UHF yagi is approx 6-8ft long
VHF is approx 6ft long
6M is approx 17ft long

They are all horisontally mounted. I am guessing it will be UHF at top, then
2 mtr then 6 mtr.
What i would like to know is if this pole is long enough to space them
vertically enough or not.
If so, what distance should they be?

Thanks

Gary
VK3LCD

Stacking beams
 

On Wed, 12 Nov 2008 18:15:37 +1100, Gary Smith wrote:

Hi, i am going in a VHF/UHF contest this weekend and have a question
about stacking beams.
We will have a pole approx 15-20ft long and want to stack the following
antennas,

1x20 element UHF yagi
1x10 element 2 Metre Yagi
1x5 element 6 Metre Yagi.

UHF yagi is approx 6-8ft long
VHF is approx 6ft long
6M is approx 17ft long

They are all horisontally mounted. I am guessing it will be UHF at top,
then 2 mtr then 6 mtr.
What i would like to know is if this pole is long enough to space them
vertically enough or not.
If so, what distance should they be?

Thanks

Gary
VK3LCD

It should work. Try to get at least a 1/4 wavelength between them (a
half wavelength would be better. If you can get the 50 MHz 3 meters off
the ground and the 70 CM on top, and split the difference with the 2
meters, it should be a good place to start. Do you have a VSWR meter
e.g. MFJ-956?

Stacking beams
 

"Gary Smith" wrote in message
...
Hi, i am going in a VHF/UHF contest this weekend and have a question about
stacking beams.
We will have a pole approx 15-20ft long and want to stack the following
antennas,

1x20 element UHF yagi
1x10 element 2 Metre Yagi
1x5 element 6 Metre Yagi.

UHF yagi is approx 6-8ft long
VHF is approx 6ft long
6M is approx 17ft long

They are all horisontally mounted. I am guessing it will be UHF at top,
then 2 mtr then 6 mtr.
What i would like to know is if this pole is long enough to space them
vertically enough or not.
If so, what distance should they be?

Thanks

Gary
VK3LCD


There seems to be too many elements on the VHF and UHF antennas. I wold
think the booms should be twice as long.

I did not have too much choice when I mounted my antennas on the tower. I
had about 15 feet of pipe out of the top of the tower. I put a M2 432
antenna at the top, went down 4 feet and put a M2 2 meter beam, both had
about a 14 foot long boom. Then 5 feet below that is a 5 element 6 meter
beam on an 18 foot boom and then the triband beam for the low bands. I am
sure they interact to some extent, but they do seem to work ok and not much
interaction of the swr when mounted on the tower. All beams are horizontal.

Stacking beams
 

Gary,

For VHF contests I usually put the lowest frequency beam on top. After
doing some modeling with 4NEC2, the higher you get in terms of
wavelengths, the lower your takeoff angle on the radiation.

I also did some modeling to look at the interaction between yagis in a
stack. For your set-up, it looks like the 6M yagi should be at the top,
the 432 in the middle and the 2M at the bottom.

73, N6FD Erich
Usually QRP Portable in DM15 50, 144, 222, 432, 902, and 1296 MHz

Gary Smith wrote:
Hi, i am going in a VHF/UHF contest this weekend and have a question
about stacking beams.
We will have a pole approx 15-20ft long and want to stack the following
antennas,

1x20 element UHF yagi
1x10 element 2 Metre Yagi
1x5 element 6 Metre Yagi.

UHF yagi is approx 6-8ft long
VHF is approx 6ft long
6M is approx 17ft long

They are all horisontally mounted. I am guessing it will be UHF at top,
then 2 mtr then 6 mtr.
What i would like to know is if this pole is long enough to space them
vertically enough or not.
If so, what distance should they be?

Thanks

Gary
VK3LCD

Stacking beams
 

Gary,
The 'best' separation distance is as much as you can get. After that,
it's more a practical thing, use what you got, do what you can. Will
that result in the 'best'/'perfect' situation? Of course not, but it
will work in the majority of cases.
A very rough ROT (Rule Of Thumb) is that UHF antennas require less
separation than VHF antennas, which require less separation than HF
antennas.
- 'Doc

Absolute best distance between antennas is at least 1 mile... in all
directions. I'm still working on mine.