Fig 1.SSB spectrum at full power from a modified IC-275E.
The serial number is 01744 and the modification is described below.
Fig 2.The noise floor with 20 dB less attenuation
between the IC275 and the RX144.
Here there is no voice signal into the microphone, otherwise
everything is as in figure 1.
Fig 3.Here is the noise floor from a modified unit.
The modification is by DF9IC who is the owner of the test
The modification is a filter in the transmitter that removes
noise the wideband noise generated in the first buffer
amplifier after the filter.
This spectrum can be directly compared to figure 2.