Posted by
David Gilbert on
Dec 05, 2011; 2:42am
URL: http://elecraft.85.s1.nabble.com/Fw-CQ-WW-DX-Contest-CW-2011-Unofficial-claimed-scores-tp7060148p7061639.html
When I experience the problem the signals are all quite close ...
probably within a 30 Hz window, but not exactly the same. My hearing
isn't as good as it was when I was younger (mostly high frequency loss
above 10 KHz), but I can tell when signals are exactly the same and if
that was the issue I'd obviously never be complaining about that. The
RIT on the K3 varies in 10 Hz steps and that difference is very
noticeable to me, so it would not normally be difficult for me to
separate a few pileup signals within that 30 Hz window if frequency was
the only factor.
As you mentioned, signals are often very close these days. People are
using narrower and narrower receive filters and that puts them more
precisely on frequency than in the past, and of course packet cluster
spots put callers pretty close on frequency subject only to the accuracy
of their rigs.
As I mentioned in another post, I think these are the key conditions for
the problem:
a. the signals need to be close enough that the children
(sum/difference mixer products) overlap in frequency with the parents
b. the signals need to be keyed, which makes me suspect at least some
gain non-linearity that varies with time. The addition of AFC-SOFT
represented an significant improvement, but not enough. Possibly some
insight into this aspect of the problem might be gained by varying the
keying speeds and observing the effect. Even there is not a time
non-linearity, though, having keyed signals is important. In real life,
keyed signals help us mentally separate signals spaced closer in
frequency than if they were not keyed.
c. The signals need to be weak, which makes me convinced that there is
a gain non-linearity at the low end. I can't really quantify just how
weak, but I would estimate less than S-2 and it seems to get worse as
the signals get weaker. I have a very low ambient noise level here and
S-1 signals are typically quite readable. Strong signals do not cause
the problem we are discussing here.
Hope some of this helps.
73,
Dave AB7E
On 12/4/2011 1:31 PM, Eric Swartz WA6HHQ - Elecraft wrote:
> We actually have a 'pile-up' generator we designed that sends multiple
> cw signals. So far it has not reproduced the issue here.
>
> What is the signal spacing you are hearing this with? All -exactly- on
> the same freq? Or spread out?
>
> 73, Eric
>
> _..._
>
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