[Elecraft] separating RFI from band noise, PX3

[Greg Troxel]

Jim Brown <jim at audiosystemsgroup.com> writes:

> Yet another example of a switch-mode power supply.  Here's a
> preliminary version of k9yc.com/KillingReceiveNoise.pdf  that might
> help.

I see you mention a 10 dB increase in levels between band closed and
band open, with the notion that if you don't see that, you have too much
local noise.  That makes a lot of sense for bands like 15m.  I don't
quite follow how one can use that rule of thumb on 6m.  For 80m,
presumably it should be quieter in the day.

I've been looking at various bands with a PX3.  Certainly my outside
(80m dipole ish) antenna is quieter than my attic dipole, but some times
it's pretty close -- presumably that's when band noise dominates.

I wonder if it's possible to have any quantitative norms.  For example,
looking at the waterfall on 30m with a 50 kHz span, and ref of -110 dBm,
I'm seeing a lot of black pixels with a fair number of dark blue.  There
are a few solid lines that are obviously interference.  And I see some
short-duration broadband pulses (horizontal lines).  So I think I have
some issues, while others might find that better than usual.

Clearly some noise sources are obvious on the panadaptor.  But most of
what I'm seeing is not obvious.  In the end I suspect that trying to
decide if I have local noise by making measurements is not going to work
or be all that useful.  (Certainly measuring with power off makes sense,
and the open-vs-closed band levels is something I'll probably try to
really measure.)

Also when using the PX3, I realize that the levels can be interpreted in
two ways.  For signals narrower than the bin size, it seems that one
should read the level as the power in the bin and hence the signal.  But
for broad noise that is much bigger than bins, I think one should be
thinking in terms of dBm/Hz.  In other words, choosing a 5x narrower
span doesn't change the level of a carrier, but it lowers broadband
noise 5x.  So referring to "-100 dBm" seems to require giving the span
(or really the bin size, if one is comparing to non-Elecraft
panadaptors).

73 de n1dam