[Elecraft] Horrible APRS QRM on 2 Meters

[Guy Olinger K2AV]

Although I agree with other points, the DSP noise blanking does not work by
pulse-closing the analog 15 kHz IF. It works in the number soup which is
after the high IF, *and* after the low IF, *and most importantly* after the
analog to digital conversion. DSP NB, being accomplished in the number
soup, is not restricted to the limits of analog methodology. While the
signal being corrected is *representative* of the low IF, it is not
accomplished *in* the IF circuitry and is subject to any outcomes of the
analog to digital conversion.

A good rule for using the IF labeled NB in the K3, is to only use it if it
makes NB on ***that particular noise*** work better, otherwise don't use it
at all. Some of the noise I have around here from time to time is better
blanked with IF + DSP. Other noise is blanked better, sometimes much
better, by DSP only. I'm to the point now where I know what each noise
around here sounds like and can put up the best NB settings right away.
Also some combo's that work well on 160 work poorly on 80m and up.

For the new user of K3 NB, remember that METHODS are also being switched as
you turn the knob, it's not at all like a simple 1 to 10 scale. You can use
a (1st) IF method, and a DSP number soup method, or IF only or DSP only.
When you use both methods, they operate separately in series, with the IF
method necessarily being applied first. It appears, to me at least, that
some DSP methods are diminished by running the IF blanking at the same
time.

For 2 and a half years I had an AC pulse noise on 160 that IF NAR4 + DSP
T1-7 or T2-7 cleared out to below the band noise in a certain 5-6 kHz range
and less efficiently away from that. Contest operation in that range was
equal to no pulse noise. It turned out to be leakage in a splice in the
13kV buried line to easterly neighbors' power transformer. When the splice
hard arced this spring, that noise went away and has never returned. The
fuse blow up on the feed pole across US 64 sounded like a bomb. It rattled
windows. They replaced all the buried 13kV line off that aerial 13 kV feed
to our transformers. Noise has never come back. Currently the IF blanker is
not useful for any noise I run into here. That could change, of course, at
any time  :>))

73, Guy K2AV

On Sat, Jul 28, 2018 at 12:10 AM, Jim Brown <jim at audiosystemsgroup.com>
wrote:

> . Fact is, that they are BOTH working in an IF, one in the first IF and
> the other in the second. FAR better to call them IF1 and IF2. NOW it
> becomes clear which is post-xtal filter.
>
>