By G8MNY

Calculate 1/4 wave lengths of 75ê coax using the coax's velocity factor & the
wave length for your frequency of interest. None of this is too critical unless
above 1GHz, where cable Z change if you bend them & cutting to length is more
of an art, so the use of a solid power slitter is more common.

Decide which harness design you want:-

        Join     Tee == to aerial                 tee ========#== to aerial
50ê =======<ðððððððð[    2x 50ê      OR   50ê =======[ 2x75ê      2x 50ê
              37ê    == to aerial                     ========#== to aerial
            (2x75ê)

eg both matching lines in a single feed plug (or socket) & an aerial plug (or
socket) with a aerial T connector. Or use the matching lines as the T with 3
plugs (or sockets). The latter is mechanically less strong, & waterproofing
may be more difficult. Alternatively you could splice in the matching sections,
but again waterproofing can be a problem.

Use good quality 75ê cable with heavy braid. You should find that 2 coxes can
be made to fit N connectors with some difficulty. Use silicon rubber or grease
to seal/fill connectors once tested.

Testing can be done with a sensitive SWR meter a 1W rig & 2x small 47ê
resistors (with minium leads) mounted one the ends of the lines to simulate the
2 aerials. This should prove the cut lengths are OK before you terminate the
aerial ends.

The Aerials must be identical types (no early/later multibeam type mix). And
mounted so that the connections feed the same side of the driven aerial element
to be in phase. If the aerials are mirror images (one upside down) and the
element cannot be rotated, then add 1/2 wave length (x Velocity factor) to one
of the 50ê aerial feeders. The two aerial feed coaxes between the spliter &
aerials must be identical lenths & type.

Aerial spacing, is variable, the manufacturers data may help, but a good guide
is about half the boom length. This rule of thumb, makes sure the aerials
capture areas do not overlap. Closer stacking/baying, gives variable results as
all the aerial elements will couple, & this will result in a different polar
diagram/gains than optimin. But closely mounted aerials with high gains are
possable, if difficult to get the distance right!

73 De John, G8MNY @ GB7CIP