On Jul 5, 11:04 pm, Cecil Moore wrote:
Michael wrote:
According to the ARRL handbook the highest gain is achieve with a
5/8ths wave spacing between the upper and lower elements. The
handbook gives the following figures for estimated gain.

3/8 wave spacing = 4.4 dbd
1/2 wave spacing = 5.9 dbd
5/8 wave spacing = 6.7 dbd
3/4 wave spacing = 6.6 dbd

It seems to works on 14 MHz (stacked dipoles at 14 MHz), but on 10
meters the single 10 meter dipole blows it away.

Quoting the ARRL Antenna Book: "It should be designed
for the higher of the two frequencies using 3/4 lamda
spacing between parallel elements. It will then operate
on the lower frequency ... with 3/8 lamda spacing.

If you have 5/8 lamda spacing on 20m, you will have
5/4 lamda spacing on 10m with poor performance.
--
73, Cecil http://www.w5dxp.com

Not only that, but will depend if feeding end fire, or broadside.
It's only as a broadside array that max gain is at 5/8 wl
spacing.
And he is feeding his as an end fire array. The elements would
need to be end to end IE: collinear, array to be fed as a broadside
array.
As an end fire, the spacing must be quite a bit closer. If I remember
right, max gain with an end fire array is appx 1/8 wl spacing.
But from my own experimenting around with them, it's not
ultra critical as far as getting them to work.
In my case, I was feeding each element with a separate
feed line, and changing lengths to steer the array.
It was quite crude, but worked pretty well.
In my case, I tried to compromise on the spacing so I
could feed it both end fire, and broadside. I think I used
about 1/4 wl.
I also used about the same scheme on 10m, using two
5/8 wl ground planes. I forgot the exact spacing I used.
It was more dictated by available mast/.vent pipe locations
more than trying to get an exact length.
But it was a compromise spacing, and I fed it both ways
depending on the pattern I wanted.