Vs: Re: Vs: Re: [1000mp] keying mod... do it

[Jaakko]

----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: "Hulkko Jaakko" <Jahla@mail.suomi.net>
Sent: Tuesday, March 18, 2003 3:08 PM
Subject: Re: Vs: Re: Vs: Re: [1000mp] keying mod... do it


> At 12:52 PM 3/18/03 +0200, you wrote:
> >Yes it is against the conventional visdom.
> >
> >According to the measurements IMD is better with NB on than off for NB
> >setting B12 (or A12) or 'higher'. For NB setting B11 (A11) or less it
does
> >not make a difference if you keep NB on or off.
> >
> >I think the main reason for the anomaly is that the test is done with two
> >tone measuerement. If the interfering signal would be of pulse type, then
> >obviosuly the results with NB on would be worse.
> >
> >So the safe bet for real interferers is to keep NB in setting B11/A11 or
> >less AND NB off (when you do not need then NB).
>
>
> Thanks, Jaako.  This really has me confused.  You and W8JI both obviously
> know what you are doing, yet you have come to totally opposite
> conclusions.  www.w8ji.com/receiver_tests.htm gives the numbers he
measured
> both with an unmodified Mark V and with one that he modified to disable
the
> NB totally by shutting off Q2009 when the NB is off.  Details on the
> modification are at www.w8ji.com/ft1000mk_v.htm.  He has confirmed to me
> that this single change is the only one responsible for the dramatic
> difference in close-in IMD between the two test series.  The Mark V went
> from being one of the worst to being second only to his modified R-4Cs.
>
> 73, Pete N4ZR
> The World HF Contest Station Database was updated 23 Feb 03.
> Are you current? www.pvrc.org/wcsd/wcsdsearch.htm
>


I do not think we have come to opposite conclusions. Stock results what Tom
and I have measured are pretty close. We both have also measured two-tone
IMDR, so we are talking about the same thing.

Tom writes in his WEB page that when NB is turned off, then "NB" Fet Q2009
gate is left floating which for sure worsens the IMD when high RF signal
levels are present compared to keeping NB on (and gate not floating). So my
results are in line with his finding here.

However - I claimed in my original post that you do not need to do any NB
mod if you use NB setting "in a controlled way" is not fully valid. If you
use NB setting as I have proposed you NB IMD negative impact is much less
than it could be, but certainly based on Tom's results much further improved
performance can be obtained by doing his mod.

So I'll do Tom's mod and report here the results...

BR, Jaakko - oh8nj