The following diagram from Henning DK5LV provides an insight into the final four stages of the µBITx PA chain. This stretches from Q90 through to the finals.
Warren WA8TOD has measured the gain and drive requirements of the transmit chain at operating frequency from Q90 through the finals. A sweep generator was inserted at C80 and the level adjusted first for a nominal 1 watt indicated on the wattmeter (Purple trace) and then five watts indicated (Blue).
– Gain of the chain varies from 56 dB at 3.7 MHz to 52 dB at 28.2
– Input levels at C80 were -24 dBm (purple) and -15 dBm (blue); note 9 dB input increase generates 7 dB output increase….. 2 dB com
pression and resulting unacceptable IMD (not shown)