Topband: Rig Comparisons

[Paul Christensen]

>
>> "Maybe I didn't read the right paper.
>Like I said,  this paper is clearly
>not on the same page with what Paul C. said.
>Paul, can you point us to the correct paper
>to read?  Rick N6RK"

Rick,

You likely read it right but the report implies too much emphasis on
needing LDMOS devices to achieve excellent linearity.  For example, if you
look at the ANAN-100D improvement, it¹s accomplished without LDMOS
devices.  The ANAN-100D uses Mitsubishi RD100HHF1 MOSFETS  and yet
excellent linearity is achieved with ADP ‹ likely due to the already low
memory effect of these devices.  ADP works best with ³low memory effect²
amplification and the reason why LDMOS technology is preferred for
solid-state, RF power devices.  Memory effect refers to changes in
amplitude and phase of distortion caused by a device's electrical changes
(e.g., hFe) due to thermal heating.

As shown in the report, many ANAN users are able to achieve excellent
linearity with ADP activated.  There¹s enough leakage from the transmitter
to the second receiver for ADP optimization to occur.  However, when an
external amp is used, a directional coupler is placed after the amp with
the sample port brought back to the second receiver.  What is a benefit of
the leakage in the first case, presents a less than optimal solution when
an external amp is used.

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.  ADP will reverse the *combined effect* of both the
transmitter and external amp.  Even so, minimizing leakage is manageable.
The ANAN transceivers were developed prior to the implementation of ADP.
I suspect that the next generation of transceivers will have better
internal shielding for use with external amps.  But it does show that even
with less than optimal RF devices like BJT and MOSFETs along with less
than optimal shielding, extraordinary results can be achieved.

The same is true for tube-based amps.  WA1OXT uses a home brew amp with a
pair of 8877s.  He¹s using an external sampler brought back to his
ANAN-100.  On air tests show a 25 dB reduction of SSB IMD components with
ADP activated.  On a clear band with ample signal, you can see the grunge
from outside his 3.5 kHz SSB passband drop like a rock from -35 dBc to -60
dBc.  With ADP activated, sharp transmit skirts are seen; there¹s nothing
else there down to the -60 dBc level.  With ADP, one can get much closer
to a very strong station to work a weak station.

For anyone wanting more info about practical ADP (PureSignal)
applications, KC9XG has included many references in the files section of
his new SDR Yahoo group.

https://groups.yahoo.com/neo/groups/KC9XG-SDR/files

Paul, W9AC