[TowerTalk] how deep a null do you need in a pattern..

[Keith Dutson]

Jim,

Being able to discern a target signal from a group is quite subjective.  The
top contesters can complete a contact that others could only dream about.
They often put one in the log that was covered up by stronger signals.  How
is this done?  Experience!

But back to your question, 1 dB should be sufficient for all but the
greenest operator.  A whole S unit would allow anybody to separate two
stations.

BTW, it is not all that difficult to make a reliable contact on 40 meters
very near a broadcast station.  Try it sometime.  During the next contest
tune up just off the center of one of those AM monster signals and throw out
a CQ on SSB.  You will likely get some replies.  It is as if your signal
rides on top of the AM carrier.

Keith

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Lux
Sent: Thursday, July 15, 2004 12:21 AM
To: Towertalk
Cc: cbduncan at earthlink.net; Jan.A.Tarsala at jpl.nasa.gov;
Mark.M.Schaefer at jpl.nasa.gov
Subject: [TowerTalk] how deep a null do you need in a pattern..

I'm doing some modeling, and an interesting question comes up, with respect
to nulling out interfering signals.

Say you have two stations, on the same frequency (or very close, so they
overlap), i.e. a pileup.  How much louder does one station need to be than
the other so that you can reliably copy it. 1 S unit (6 dB?)  1dB (that's
sort of the magnitude of a "Just Noticeable Difference")?

Different for voice or CW? (CW makes it a bit easier, because it's unlikely
that they're actually zero beat with each other, so there's a slight pitch
difference to help)

I realize that there's a lot more to it in practice (voice pitch, cadence,
slight differences in carrier frequency, etc. all help separate them
mentally).

What about if they're booming in at S9+?  S2-S3?  Down in the hiss?

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