[Elecraft] K3S Audio buzz on transmit, especially AM

Fri Apr 26 21:11:31 EDT 2019

A few more data points:

Changing TX EQ, including cutting the first 4 bands all the way down to -16
had no effect on the received signal.

Plugging in some headphones, turning the TX Monitor up all the way, I don't
detect the hum in the TX monitor signal either in TX test mode,
transmitting into a dummy load, or even transmitting into the antenna with
very low power.  If I turn up the Line In level, I just hear expected white
noise on the TX monitor.  So at least as far along the path as the TX
monitor, there's no hum or buzz introduced.

Switching the receiver (a KX3) to USB mode and using one leg of a
buddistick as an antenna so I can walk around, the noise received around
the house and outside is around S4 when transmitting about 100mW into the
antenna, though it varies some as I walk around.

I do have a set of power lines running through my back yard, and where I
live in San Mateo, you're always near somebody's wiring for something,
unfortunately... my neighbor's south wall is possibly as far as 8 feet away
from my north wall, etc.

It looks like two phases running along the top, then a transformer to two
phases and a neutral along the bottom, to which people's houses are
connected.

We also have underground utilities on our street, including a big green
transformer that sits in the corner of our front lawn.

I think the next test will be to take the K3S and the KX3 some distance
away from all of these things and see if the hum goes away, and if it does,
then figure out what thing the K3S needs to get away from in particular.
If it's the powerlines in my back yard or the transformer in my front yard,
then that'll be a difficult problem.

   Nick

On Fri, 26 Apr 2019 at 17:28, Bob McGraw K4TAX <rmcgraw at blomand.net> wrote:

> Yes but the EQ is in the digital path.  The EQ should be done there,
> preferably after the MIC input.   The AM BW does not attenuate the end like
> the SSB filter.
>
> I suggest -16 dB on the first 3 bands.
>
> Bob, K4TAX
>
>
> Sent from my iPhone
>
> > On Apr 26, 2019, at 6:38 PM, Nicklas Johnson <nick at n6ol.us> wrote:
> >
> > Flat, except I turned the first one down a few notches, which doesn't
> > really do much in my case because both the microphone and mixer that I
> use
> > (when they're actually connected) roll off below 150 and 80 Hz
> > respectively.  It had previously been suggested to me that rolling off
> low
> > frequency cruft is a good idea for AM and SSB.
> >
> >   Nick
> >
> >> On Fri, 26 Apr 2019 at 15:57, Bob McGraw K4TAX <rmcgraw at blomand.net>
> wrote:
> >>
> >> I recall commenting earlier.  What TX EQ values are being used for AM. ?
> >>
> >> Bob, K4TAX
> >>
> >>
> >> Sent from my iPhone
> >>
> >>> On Apr 26, 2019, at 5:48 PM, Nicklas Johnson <nick at n6ol.us> wrote:
> >>>
> >>> My desk in this case sits adjacent a wall, and there's only a shower on
> >> the
> >>> other side of that wall.  I did turn off everything in the vicinity of
> >> the
> >>> desk and all the lights in the room (I've in fact heard a very similar
> >> hum
> >>> from the switching power supply for my mixer, and my first thought was
> it
> >>> was this that was being picked up), but I didn't turn off the computer
> on
> >>> the other side of the room.  In this case it will be easier to move the
> >> rig
> >>> outdoors with a battery than it will be to turn that computer off for
> the
> >>> moment.  It would have to be an impressively/obnoxiously strong
> magnetic
> >>> field from that side of the room to influence the transformers inside
> the
> >>> rig 8 feet away, but it's worth trying and simple enough to rule it
> out.
> >>>
> >>>  Nick
> >>>
> >>>> On Fri, 26 Apr 2019 at 14:51, Don Wilhelm <donwilh at embarqmail.com>
> >> wrote:
> >>>>
> >>>> In addition to operating from a battery isolated from the solar
> system,
> >>>> I would recommend that you do a quick test - remove all cables from
> the
> >>>> K3S except the power cable and a coax to a dummy load.  Power down all
> >>>> power supplies in your station, including any desk lamps.
> >>>> Go into Transmit by tapping the XMIT button.
> >>>> Is the hum still present?  If not, then start connecting things to
> your
> >>>> K3S one at a time, doing the same test after each thing connected.
> >>>>
> >>>> Of course, if the hum is present with nothing connected, contact
> >>>> support at elecraft.com - but I cannot imagine a hum with harmonics of
> 60
> >>>> Hz being induced if you take away all the 60 Hz operated sources in
> the
> >>>> area.
> >>>>
> >>>> 73,
> >>>> Don W3FPR
> >>>>
> >>>> --
> >>> *N6OL*
> >>> Saying something doesn't make it true.  Belief in something doesn't
> make
> >> it
> >>> real. And if you have to lie to support a position, that position is
> not
> >>> worth supporting.
> >>> ______________________________________________________________
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> >>
> >>
> >
> > --
> > *N6OL*
> > Saying something doesn't make it true.  Belief in something doesn't make
> it
> > real. And if you have to lie to support a position, that position is not
> > worth supporting.
> > ______________________________________________________________
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>
>

-- 
*N6OL*
Saying something doesn't make it true.  Belief in something doesn't make it
real. And if you have to lie to support a position, that position is not
worth supporting.