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Section 4.1: Resistance Test (mandatory)
The control cable uses 4 wires per motor (one motor in each element housing unit (EHU)). Each motor
has two wires for each of its two motor windings. This test assumes the antenna is connected to one end
of the control cable and the measurements are taken at the 25-pin connector that mates to the controller
(disconnected from controller). You need an ohmmeter capable of measuring 15 – 35 ohms with reason-
able resolution or at least one that you can tell the difference between a dead short and 15 ohms.
Step 1: Be sure the 25-pin DSUB control cable connector is disconnected from the controller (your con-
trol cable should not be plugged into the controller until the Resistance/Open Circuit test is completed).
Step 2: Hold the DB25 connector so you are looking at the pins with them pointing at you or open the
back shell of the DB25 field splice. If prodding the pins directly, orient the connector so the row with 13
pins is on top, now the upper left-hand pin is pin 1. See Figure 4.11 for reference. If you decide to open
the case of the connector, reference the pin number marking on the PCB (Figure 4.12).
Step 3: Measure the resistance between the pin pairs indicated. You only need to measure the re-
sistance of wires that correspond to the elements on your antenna. The required pin pairs to measure
are shown in the table below. You should read between about 15 ohms to 30 ohms depending on cable
length between the pins listed below. Record your results in the “Results” column. (100’ is about 23
ohms).
Figure 4.11
Figure 4.12
Resistance Test Table
Pin Pair Antenna Element Expected Resistance
Results (ohms)
1-2
Driven
~ 20 Ohms
3-4 ~ 20 Ohms
5-6
Director
~ 20 Ohms
7-8 ~ 20 Ohms
EHU WIRING TESTS
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