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Page 29
When wiring the EHU’s on the DB18 Yagi, it is important to know that there are two different types of
EHU. The two end “loop” elements can function as either a passive element or a driven element, de-
pending on what band or direction that antenna is in. Because of this, the end elements utilize relays
inside the EHU. The center, or “straight” element functions solely as the driven element when on 20m
thru 6m. There is no relay inside this EHU because its purpose is singular.
There are wiring differences that need to be followed as well—the center EHU, which has no relays,
uses 4 conductor control cable to power the stepper motor. The end elements, with the relays, uses 6
conductor control cable, 4 wires to control the stepper motor, and 2 wires to control the relays. It is
critical that the right control cable is used for the respective EHU or the antenna will not function cor-
rectly, and the electronic controller could be damaged.
This brings up an important note: NEVER DO ANY WIRING WHEN THE ELECTRONIC CON-
TROLLER IS CONNECTED TO THE CONTROL CABLE. Even if the power is turned off of the con-
troller, damage can occur. This is the number one cause of antenna installation failures, so please be
sure to heed the advice.
Figure 3.10 gives an overview of the inside of a SteppIR EHU.
Control cable tray
for routing cable
out of EHU
Relays (this space will
be empty if the EHU
has no relays)
6 position EHU terminal
header (4 position used
for EHU’s with no relay)
Element support
tube
Balun (the balun is only
inside EHU’s that are
driven elements)
Spring reel for
copper strip
SO239 connector
(for driven ele-
ment only)
Sprocket / platen
assembly
CHAPTER THREE
SECTION 3.1
MOUNTING THE EHU’S ON THE BOOM (continued)
ELEMENT HOUSING UNIT (EHU) WIRING OVERVIEW
FIG. 3.10
Serial # sticker
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