[Elecraft] PX3 Problem?

[Dale Boresz]

Hello Dave,

Just checked my KX3/PX3 and with no antenna, I am also seeing spur peaks
about 25 to 30 dB above the noise floor.

With the PX3 SPAN set to 30 KHz:

On 20 meters, when I turn the preamp ON (20dB preamp setting), and connect
my HexBeam, I only see 20m band noise at about -112 dBm; there is no sign
of the spurs. If I turn the preamp OFF, then I do see some of the spurs
about 5 - 8 dBm above the noise floor.

To provide some idea of my actual noise floor on 20 meters, my P3 indicates
-124 dBm (also with a SPAN of 30 KHz), and three other SDR radios also read
-124 dBm on their respective panadapter displays, each set to a span of 30
KHz.

Do you still see any of the spurs with your antenna connected on 20 meters,
and the 20 dB preamp engaged?

73,

Dale - WA8SRA






On Sun, Jul 16, 2017 at 10:47 PM, Dave Sublette <k4to at arrl.net> wrote:

> Using just one of 20 “extra” spurs, I measuredthe spur peak at -90 with
> the preamp on. Base line is -125 with it on.
>
> Turning off the preamp, the peak is -75, base line -112.
>
> The s/n remains basically with preamp on and off.  The main thing is,
> Those spurs were not there previously.
>
> I just took the PX3 out to the shop and hooked it to another supply.  The
> spurs are still there.
>
> Dave
> > On Jul 16, 2017, at 10:22 PM, Don Wilhelm <donwilh at embarqmail.com>
> wrote:
> >
> > Dave,
> >
> > The KX3 is designed to be operated with the preamp on most of the time.
> The only reason to turn it off is when extremely strong signals are
> encountered.
> >
> > The preamp eliminates many spurious signals that are actually out of
> band due to its signal rejection "filtering".  That has nothing to do with
> the sensitivity, and it can kill extraneous results such as you are seeing.
> >
> > If it makes those responses substantial with the preamp on, then there
> may be a problem to be addressed.
> >
> > 73,
> > Don W3FPR
> >
> > On 7/16/2017 10:07 PM, Dave Sublette wrote:
> >> Good point.  However I am on 20 meters, which really doesn’t need the
> preamp.  Besides, the spikes are 40 dB high or so.  No, this behavior is
> definitely looking like a failure.  I have one more thing to try.  I will
> carry it out to the shop in my garage and plug it in.  If it is the same
> there as in here, it’s not any external influence.  Thanks for hanging in
> there with me.
> >> 73,
> >> Dave
> >>> On Jul 16, 2017, at 9:56 PM, Dale Boresz <dmboresz at gmail.com> wrote:
> >>>
> >>> Dave, make sure that the preamp is engaged on your KX3. If the preamp
> is off and you are receiving on a quiet band, you'll see "stuff" that would
> normally be covered by the band noise. Turn on the preamp, and the
> artifacts that you're seeing should be pushed below the noise floor of just
> about any band.
>
>