KX3 PSK-31 IMD on Low Batteries

[Kevin - K4VD]

I probably should have expected this and took action before anyone had to
mention it.

I was using a KX3 on internal battery. I was running PSK-31 using DATA-A at
3 watts. I use an external soundcard (ASUS Xonar U7) and the laptop is an
HP Spectre running Win10 and DXLab suite. Rig control and the sound card
run off a USB hub. Antenna is a 160 meter OCF and I was on 40 meters.

The last QSO was with Eric KB3CNK. He's a few hundred miles from me. He
reported my signal was strong but that he saw some harmonics or splatter on
his waterfall.

I immediately backed down on the audio a little bit (5th bar flickering to
4th bar flickering) but he said it made no difference. My next thought is
some RF getting back into the audio which, with an OCF, wouldn't be unheard
of. I wasn't looking forward to tracking that down. I've got puka beads at
the feed and rig ends of the coax.

Then I noticed my internal battery voltage was down to 8.8V key down. I put
on the external battery which brought it up to 12.1V key down and he said
the signal looked beautiful (still 4th bar flickering).

The panic subsided. I'll need to be a little more aware of my battery
voltage in the future. Viva la simple fixes.

73,
Kevin K4VD
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[Don Wilhelm]

Kevin,

As you noticed, the IMD of any transceiver is degraded when operating at
a voltage below its design point.
That fact is independent of the mode.
Certainly, the KX3 will "work" down to 8 volts, but not without
consequences.

I do not know the design point for the KX3 PA, but I would figure it is
11 volts based on using fully charged NiMH batteries.

73,
Don W3FPR

On 8/9/2016 11:00 AM, Kevin - K4VD wrote:

> I probably should have expected this and took action before anyone had to
> mention it.
>
> I was using a KX3 on internal battery. I was running PSK-31 using DATA-A at
> 3 watts. I use an external soundcard (ASUS Xonar U7) and the laptop is an
> HP Spectre running Win10 and DXLab suite. Rig control and the sound card
> run off a USB hub. Antenna is a 160 meter OCF and I was on 40 meters.
>
> The last QSO was with Eric KB3CNK. He's a few hundred miles from me. He
> reported my signal was strong but that he saw some harmonics or splatter on
> his waterfall.
>
> I immediately backed down on the audio a little bit (5th bar flickering to
> 4th bar flickering) but he said it made no difference. My next thought is
> some RF getting back into the audio which, with an OCF, wouldn't be unheard
> of. I wasn't looking forward to tracking that down. I've got puka beads at
> the feed and rig ends of the coax.
>
> Then I noticed my internal battery voltage was down to 8.8V key down. I put
> on the external battery which brought it up to 12.1V key down and he said
> the signal looked beautiful (still 4th bar flickering).
>
> The panic subsided. I'll need to be a little more aware of my battery
> voltage in the future. Viva la simple fixes.
>
>

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