Tom,
Also consider a situation where a solid-state transceiver is driving a class B
amp with, for example, -20 dBc 3rd order IMD -- and that IMD is much worse than
the driving transmitter. In that case ADP is correcting IMD products where IMD
is generated primarily from the amp.
Paul, W9AC
Sent from my iPhone5
> On Aug 3, 2014, at 10:25 AM, "Tom W8JI" <w8ji@w8ji.com> wrote:
>
> 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
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|