by 5B4AIY » 28 Mar 2021 07:09
Hi, Marcel,
Since the input attenuator uses discrete components it would certainly be possible to increase the attenuation. For example, if the attenuation steps were increased so that the 2dB attenuator was 3dB, and the 4dB attenuator was 5dB, then this would give steps of 0, 3, 5, and 8dB. With 8dB attenuation the amplifier's gain would reduce from 15dB to 7dB, and for an output power of 50W, +47dBm, you would need an input of +40dBm, or 10W. If you opt to do this bear in mind that the power rating of the resistors forming the attenuator would need to be sufficient to dissipate the input power.
As for the PTT switching, the amplifier repeats the input key line to the output socket, so connect the SDR PTT keyline to the amplifier, and take the amplifier's output key line to the linear. There is no need for a parallel connection. Have a look at the Juma MAIN BOARD, T/R, ATTENUATOR, CURRENT SENSE schematic. The NOT_KEYIN line, active low, switches TR1, which repeats this by switching the NOT_KEYOUT line with TR2. The T/R switching is connected via a 3.5mm socket on the rear panel. This uses a stereo 3.5mm plug, with the NOT_KEYIN line wired to the tip, and the repeated NOT_KEYOUT wired to the ring.
Adrian, 5B4AIY