User's Manual

VHF UNIDIRECTIONAL AMPLIFIER TECHNICAL MANUAL
8
Output Power Level – MSA#2 Setting
The limited output power of the Amplifier module is Factory set with a 2 carrier input while monitoring
IM products, such that these IM products do not exceeding -13 dBm at the diplexer common port. This
Factory set defines the maximum operable power, since the PA will automatically shut down if higher
output power is forced. The unit must not be re-adjusted for giving higher output. However, re-adjusting
the MSA# 2 for lower output power is permitted, and the desired level could be easily obtained with-in
±1.0dB of accuracy.
Since the PA unit has fixed gain, the output power could be settled to the desired level by mean of the
MSA#2 on the VGA unit. The MSA#2 attenuation can be set from 0 to 15dB per 1dB step, via a
hexadecimal switch (16 positions from “0” to “F”).
The output power re-setting must be done with the presence of the channel filters and diplexers in the
uplink and downlink paths. Since the VGA does have extra gain, a total insertion loss up 5dB on the
channel filter(s) still is acceptable, with no deterioration on the power level, or the IM products.
Depending upon the carrier frequency and channel spacing, the maximum operable power can be varied
as shown below in Table II.
Table II: Max operable power ratings to
comply with FCC and Industry Canada specs.
(Diplexer loss not included)
COMPRODmodelnumber: UDA138225
Frequencyband: 138225MHz
Powersupplies: ACorDC5.4V&48V
Frequency
(MHz)
MaxOperablePowerRating(dBm)
CHSpace
6.25KHz
CHSpace
12.50KHz
CHSpace
25.00KHz
138 29 29 29
145 30 30 30
155 31 31 31
175 31 31 31
215 30 30 30
225 29 29 29
VGA and PA output port termination
Due to the ALC loop, the VGA maximum gain can be as high as 85dB. During the installation, it is
recommended to set the MSA#2 at the position F (max att.) then gradually increase the VGA output
power to the desired level. The VGA input and output return loss are low (< -18dB) and can be
connected directly to the diplexer or mid-stage filter.