BLUES30/50NV
ELETTRONICA
27
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User Manual
Rev. 1.0 - 29/11/16
7.4 Power amplifier
The final power stage is enclosed in a totally shielded metal container fixed to the
central part of the device.
The RF signal coming from the main board reached the pilot, it come amplified
and sent to the final stage which takes care of final amplification up to 30/50W.
The amplifier is made in three stages. The first is made with one BFG35, the second
with two BFG35 in parallel, and the last with two MRFE6US25NR1.
In addiction to the actual RF amplification, this circuit carries out the following
functions:
• Measures of the forward and reflected power by means of directional
couplers
• Low-pass filtering of the RF signal in output
This board also features an RF sampling of approximately 7dBm at 30/50W with
respect to the output, which is available on a BNC connector below the transmitter
output connector. This sample is is useful for verifying the characteristics of the
carrier, but not for verifying those of upper harmonics.
7.5 Control board
The main function of this board is to check and correct the MOSFET polarization
voltage of the RF amplifier section with a feedback mechanism based on the
reading of the power really delivered (AGC).
The voltage is also affected by other factors, such as:
• Excess of reflected power.
• External AGC signals (Ext. AGC FWD, Ext. AGC RFL).
• Excess of temperature.
• Excess of absorbed current from the RF module.
It is also able to perform the reading, and the standardization, on different
parameters measured such as: forward and reflected power, current absorbed by
RF power amplifier and temperature.
