130
Options List
B.8.6
Output Loading (Modulated IRIG-B)
Driving modulated IRIG-B loads is simpler than for unmodulated IRIG-B loads because input impedances
are substantially greater (several kilohms typically); and most modulated IRIG-B loads include some sort
of leveling or AGC amplifier, providing tolerance for signal level variations. Consequently, modulated IRIG-
B loads may be connected with greater ease; Arbiter Systems recommends that you simply calculate the
effective parallel load impedance of the parallel-connected loads. As long as the load impedance is 50 Ω or
more per driver, and the loads will accept a 3 Vpp minimum signal level, and the connecting lines are short
(5 Ω or less loop resistance), then no further analysis is required.
As with unmodulated signals, two or more drivers may be paralleled if desired. Unlike the current-
limited unmodulated IRIG-B drivers, the modulated IRIG-B drivers are impedance-limited and will operate
properly into any load impedance, including a short circuit.
If the loop resistance is greater than 5 Ω, then it may be treated as additional source resistance in series
with the 20 Ω driver impedance. This source resistance then forms a voltage divider with the load. See
calculation for “Output Level at Load” below by using Equation B.1.
For Example (see figure below)
Using Equation B.1 to calculate the Output Level at Load;
(B.1)
V
=
R
load
R
S
+
R
loop
+
R
load
×
4
.
5
Source impedance of driver: 20 Ω
Loop Resistance: 10 Ω
Parallel Load Resistance: 75 Ω
Output Level at Load V = (75
÷
105)
×
4
.
5 = 3
.
2 Vpp
