Fixed Gain Amplifiers; Detector - Aeroflex NAV 2000R Operation Manual

With the RF leveling VGA nominally biased at 0.4 volts (U2 pin 8) the gain will be about 17 dB. Thus, the
carrier level at the output will be near the -19 dBm level. For a 100% modulated carrier, this means that
the peak will be at the -13 dBm level nominally.
Since variations in gain and frequency response of the three power boosting amplifiers may be as much
as 5 dB, the peak of the RF signal level at the output of the RF Leveling VGA could be as high as -8 dBm.
This is only 5 dB below the output compression point of this amplifier but has no appreciable effect on
distortion.
The RF output, of the RF Leveling Amplifier is single ended. The other output is match terminated in 50
Ohms.

4.5.19 FIXED GAIN AMPLIFIERS

The two fixed gain amplifiers on the RF Modulator Board boost the nominal RF carrier to 0.0 dBm at the
output.
The RF level from U2 is attenuated by a 6 dB pad and will be nominally -25 dBm at the input of the first
Fixed Gain Amplifier. Remember, that due to automatic leveling, this level may vary by +/- 5 dB. The first
Fixed Gain Amplifier offers about 22 dB of gain with a compression point of about 10 dBm.
uncompensated frequency response should be approximately 1 dB. The nominal output of this amplifier
is about -3 dBm. Note that L1 and L2 have been selected to improve the frequency response of the
amplifier.
The second Fixed Gain Amplifier offers 9 dB of gain with a +16 dBm 1 dB compression point. The output
of this amplifier will have a nominal carrier level of about +6 dBm. At the output of the second Fixed Gain
Amplifier, a small portion of the RF power is sent to the Detector and the main power path is attenuated
by a 3 dB pad and sent to the RF Modulator Board output connector E2.
At the output of the RF modulator board, the nominal carrier level should be at the -3 dBm level. Note
that the programmable step attenuator and output relay network have about -3 dB insertion loss so that
there will be a 0.0 dBm carrier level at the output of the NAV 2000R - if no other attenuation is inserted by
the programmable attenuator.

4.5.20 DETECTOR

The Detector circuitry demodulates the RF carrier to provide an audio signal that is independent of
temperature and RF frequency. This assures proper operation of the RF leveling and detected audio
Hi/Lo circuits. Calibration adjustment is also provided for the detected audio signal, which is used for
self-test.
The frequency response and detected audio level temperature dependence are handled by two
independent parts of the Temperature Compensated Detector circuitry.
leveled over the 25 MHz to 450 MHz range by capacitor C26 and resistor R14.
The temperature compensation circuitry involves CR1, CR2, Q1, and Q2 and is achieved by using the
same type diode as the detector, but used in a compensation capacity. With an increase in temperature,
the Voltage vs. Current curve of detector CR1 shifts. However, the bias current of CR1 is controlled by
CR2, the compensating diode. When the bias point of CR1 changes due to a temperature fluctuation, the
bias current provided through CR2 offsets the change. Q1 and Q2 provide the current drive for the
network.
NAV 2000R SIGNAL GENERATOR - REV. 0 – JULY 26, 2007 - PG 4-22
Aeroflex Operation Manual
The frequency response is
The