- 2 -
sometimes the difference between barely readable and having a strong signal which can provide the
performance edge needed to work rare DX - and win contests.
It is therefore desirable to not only change azimuthal direction by rotating the antenna, but also
elevation angle by switching between antennas at different heights above ground and/or changing
the phase relationship between multiple antennas. The old standard system in stacks was to activate
or disable specific antennas in the stack to change pattern. In general, gain remains higher when all
antennas are driven and phase is changed. This system allows either phase inversion or completely
disabling any antenna.
The
DXE-PS-2B-P
Pro-Stack Broadband Two Antenna Phasing System provides the greatest
flexibility from two identical antennas. This system contains a broad-bandwidth high-power 2:1
impedance matching transformer. This eliminates common requirements of using mixtures of 75Ω
and 50Ω cables for impedance matching.
A central stack-box location is best. Feedlines to each antenna from any stack-box should match
the antenna system impedance and have the same electrical length. Feedlines need only be long
enough to reach comfortably from each antenna to the stack-box. While it is best to have feedlines
equal electrical lengths, total errors of twenty electrical degrees or less have only a minor impact on
system performance. With such wide tolerances in cable lengths, cutting similar cables to equal
lengths will suffice. There is no need to closely phase-match cables.
Larger Array Building Blocks
The
DXE-PS-2B-P
Pro-Stack
Broadband Two Antenna Phasing System control box works in
conjunction with identical boxes, or in combinations with 3-stack boxes, to build larger stacked
arrays. For example, four antennas are stacked using three
DXE-PS-2B-P
boxes. In this example,
two
PS-2Bs
would be centrally located; one between the upper and lower antenna pairs, and each
antenna would be fed through equal length cables. A single
PS-2B
located in the middle of the stack
feeds the upper and lower boxes through equal lengths cables. This would allow the user to take any
antenna or combination of antennas off-line, or feed any antenna or combination of antennas out-of-
phase. Keep in mind out-of-phase systems generally have more gain than systems that disable
antennas.
The best arrangement for larger stacked systems is feeding antennas in pairs, with the pairs fed from
other stacking boxes. This is a distributed or branched feed system. All cables at any branch level
should be equal length. While it is best to avoid length errors, accumulated errors totaling 20-
degrees or less have a minimal affect on gain and positioning of lobes. With such wide tolerances in
cable lengths, cutting similar cables to equal lengths will suffice. There is no need to closely phase-
match cables.
Multiple antenna arrays require modeling with software such as “
EZNEC
” by W7EL to examine the
multiple patterns possible by reversing phase and dropping antennas in a large system.
