[1000mp] IP3 on Rob Sherwood's site

[Chuck Lewis]

Thanks, Bill, that answers my question.

Chuck, N4NM

----- Original Message ----- 
From: "Bill Tippett" <btippett at alum.mit.edu>
To: <1000mp at mailman.qth.net>
Sent: Wednesday, October 13, 2004 7:53 PM
Subject: [1000mp] IP3 on Rob Sherwood's site


> 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.
>
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