Service Manual Part 1
80
L114 and L116 form a 50Ω delay line that provides the delay necessary for the noise
blanker to detect and clamp noise pulses and also provides a high impedance point for
the signal to be clamped.
The 10.7MHz output feeds the plug-in IF PCB through R128, R129 and R132 which pro-
vide the attenuation equivalent to the second mixer of the T2000-300, T2000-400, T2000-
500 or T2000-600.
Each sub-block within the front end has been designed with 50Ω terminations for ease
of testing and fault finding.
8.8 11111'<#
The VCO output from the PIN switch is amplified to 500mW by a two stage broad band
exciter (Q301 and Q302) with approximately 2ldB of gain. Q301 is operating into com-
pression to prevent changes in VCO drive affecting output power. This output power is
controlled by varying the collector voltage on Q302, via Q303, Q304 and the feedback
loop from the PA. The power settings (maximum, high and low) are under microproces-
sor control and are set for each channel by programming. R308A, R308, R309 and R310
provide approximately 1dB of attenuation and isolation between the exciter and power
amplifier.
8.8 111117!&
The 500mW exciter output is amplified to 30W by Q305 and Q306. The T2000-200 power
amplifier has no tuning, and when the output power is set to 25W the variation across
the 22MHz switching range should be less than ±2W.
The high level RF signal passes via the Tx/Rx PIN switch, the low pass filter and the
directional coupler to the antenna connector. The power level is sensed by D301 on the
directional coupler and this voltage is fed back to the power control operational ampli-
fier via RV324. RV324 on the RF PCB sets the high power and RV507 on the logic PCB
will adjust the low power.