Topband: Rig Comparisons

[Tom W8JI]

You¹ll final several references of ANAN users who have improved internal
transceiver shielding so that RF detection comes only from the sample port
and not internal leakage.  Otherwise, the ADP algorithm is trying to
simultaneously correct for non-linearity of two amplifiers (internal and
external) and not just one  < when only the external amp requires IMD
optimization.  >>>>>>>>>

I know Paul knows how it works, but the explanation was incorrect.

The bulk of distortion is almost always, with the exception of a few radios 
and amplifiers, from the transceiver. Most external amplifiers, with the 
exception of the common poorly designed tetrode systems and low voltage 
solid state amps, are significantly more linear than the exciter. A grounded 
grid triode amplifier using 8877 tubes, or even 811A tubes, is significantly 
cleaner than most radios (even when the amplifier is being hammered). The 
general exception are tetrodes with improper screen and bias regulation that 
lack the heavy negative feedback of grounded grid amps, or the rare radios 
with exceptional transmitter linearity.

Distortion correction *must* include the exciter, but it must be at the 
antenna port.

Unwanted coupling from the exciter does not cause the ADP system to correct 
the exciter. Unwanted coupling introduces a sample that is not 
representative of what is actually on the antenna port. This effect is 
commonly observed when we try to monitor our own transmitters with other 
receivers at the operating position. We often hear hum, noise, distortion, 
and artifacts that are not on the antenna line.

73 Tom