User Manual

USER’S MANUAL SERIES 48750 RF REPEATER
5 120556
INTERMODULATION PRODUCTS, AGC, AND OUTPUT POWER
A general requirement exists within 47 CFR 90, Subpart I and 47 CFR 22, Subpart K regarding
emissions outside of any particular channel of operation. As a general rule, there shall be no spurious
emissions greater than {43 + 10 Log10 (Power Out watts)} dB below the carrier Power Out (dB) level.
This is always equivalent to a fixed level of -13 dBm maximum spurious emission.
Radio Frequency Systems has designed the 48750 amplifier line using a combination of an automatic
gain control and a low distortion power amplifier to achieve maximum output while automatically
maintaining spurious intermodulation levels below -13 dBm for any number of input channels.
AGC automatically varies the overall gain of the system by up to 20 dB. The gain set by AGC is a
function of the total power present in the amplifier at the final output power amplifier stage. The total
power level is the sum of all signals within the applicable bandwidth. This includes all active channels, all
intermodulation products, and any other noise power in the band.
Table 4 lists the typical output power per channel which can be expected from the amplifier for a given
number of active channels operating at equal input levels. The numbers given in Table 4 are valid only
when operating within the active AGC region of the AGC amplifier stage. Operation in the AGC region
occurs for input power levels such that the sum of total input power plus the amplifier's maximum gain
exceeds the stated maximum level for the given number of channels. AGC will then actively limit the total
output power to the stated maximum levels.
TABLE 1. TYPICAL OUTPUT POWER

  
  
  
  
  
  
  
  
AGC AUTOMATIC SHUTDOWN
When the automatic gain control circuit reaches its control limit, power to the power amplifier stage is
cut. This feature ensures that spurious emissions are never allowed to exceed permissible levels. Note
that only the path (Tx or Rx) which has reached its control limit is shut down.
Shutdown will only occur if the AGC control limit is reached and maintained for about a half second.
Power is then cut for 5 to 7 seconds. After this time-out, power is brought back on-line. If the overload
condition is still present, shutdown will again occur in about a half second. This cycle will be repeated
until the condition causing AGC to reach its limit is removed. Conditions which can cause AGC to reach