ROC364 Instruction Manual
4-11 Communications Cards Rev Jun/05
4.3.2 Setting Modem Card Attenuation Levels
The output attenuation of the Leased-Line and Radio Modem Communications Cards is set by default to
0 dB (no attenuation). This level can be reduced, as necessary, to better match the modem output to the
line or radio. The adjustment is made by plugging a resistor into the card at the location labeled R2.
Refer to Figure 4-9. Table 4-3 lists resistor values and the amount of attenuation they provide.
Table 4-3. Radio and Leased-Line Modem Communications Card Attenuation Levels
Attenuation
(dB)
R2 Value
(Ohms)
Attenuation
(dB)
R2 Value
(Ohms)
–2 205 K –12 15.8 K
–4 82.5 K –14 11.5 K
–6 47.5 K –16 8.66 K
–8 30.9 K –18 6.65 K
–10 21.5 K –20 5.11 K
Notes: 1. All resistor values are nominal; 1% ¼ W resistors are acceptable.
2. Attenuation for leased or private-line operation or for a GE MCS
radio is normally in this case, no resistor is needed.
3. Attenuation for a GE TMX radio is typically –20 dB.
4. Attenuation for an MDS radio is typically –10 dB.
R2
COM PORTS
Figure 4-9. Location of Attenuation Resistor
R2 Attenuation Resistor
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