[1000mp] IP3 on Rob Sherwood's site

[Bill Tippett]

N4NM wrote:
 >It appears, from the superscript (b), that Rob used the preamp when
evaluating the Mk-V (and others). Is that everyone else's interpretation?

         Superscripts apply only to the column they appear in, and Preamp
On (b) is used ONLY for sensitivity measurements (i.e. Noise Floor,
AGC Threshold, Sensitivity, etc.)  Rob, like ARRL, W8JI and others
normally quote IMDDR3 and BDR with Preamp Off to be consistent.

 >Surely the preamp affects IP3 adversely, right?

         Correct, which is why IMDDR3 and BDR are normally measured with
Preamp Off.  Actually ARRL provides their measurements with Preamp
both On and Off, but all tabular comparisons I know of use Off for
all rigs.

K9VUJ wrote:
 >Another question I would ask is if the preamp is used is it in tuned or
flat (menu 8-4)?

         Like ARRL, Rob makes measurements at 14 MHz.  Therefore it really
makes no difference since bands below 12 meters and above 40 meters
revert to the Flat preamp on 14 MHz, even if 8-4 is set to Tuned.  If
my memory is correct, there are actually 3 different MP preamps:

1.  Tuned on 10/12m provides about 10 dB extra gain over Flat.
2.  Tuned on 160/80/40m provides a little less gain than Flat.
3.  Flat is auto-selected on 30-15 meters even when 8-4 is set
to Tuned.

I no longer have an MP manual but that is how I remember it.

K5UJ wrote:
 >my understanding of the mod is that it affects performance
(if it does anything at all) above 20 m.

         More likely the other way around unless you are using very
high gain antennas on the high bands.  The reason being that
extremely strong (S9+30) interfering signals on the low bands are
much more common than on the higher bands.

                                         73,  Bill  W4ZV

P.S. There is no IP3 measurement on Rob's site.  IMHO IP3 is an
academic measurement whereas IMDDR3 and BDR are better measurements
that simulate the real world problems of phantom IMD products (from
multiple strong signals) and front-end desense (BDR) from a single
extremely strong signal.