Sorry for the dyslexia. I've been meaning to type APD, not ADP.
Paul, W9AC
Sent from my iPhone5
> On Aug 3, 2014, at 10:58 AM, Paul Christensen <w9ac@arrl.net> wrote:
>
> 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
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