[Elecraft] Powering a K3s from a battery?

[Bill Mader]

Actually, IMD in the PA increases significantly as battery voltage drops!
For example, during Field Day a few years ago someone kicked off the
generator power to our SSB station which kept operating on the back-up
battery.  Sometime later the CW captain stopped by asking if we had changed
anything.  He could hear "splatter" from our 20m signal on his 20m rig.
This was not the case earlier in the day.

I checked everything and discovered the AC power issue.  I turned the outlet
switch back to On and checked with the 20m CW operator.  His reception had
immediately cleaned up!  He no longer heard anything from 20 SSB the rest of
the (non-contest) event.  BTW, we went on to take 4th place overall with
just six transmitters (2012).

When driving a KPA500, this is much less of an issue since the K3 runs
typically under 30 Watts for 500 Watts from the KPA500.  NC0B has spoken
frequently, in less than glowing terms, about IMD issues in 12 VDC (nominal)
PA's.

I've seen a number of comments recently that some folks don't care if their
radios' TX IMD is high.  That attitude is exemplified in many DX pileups.  I
have raised my power supply's voltage in an effort to keep my TX IMD as low
as possible based on my reading and empirical evidence related above.

73, Bill, K8TE
Albuquerque DX Assn

Message: 23
Date: Tue, 29 Dec 2015 15:57:18 +0000
From: John Macrae <kk4oyj at gmail.com>
To: Marc Veeneman <mhvnmn at gmail.com>, Juliean Galak <jgalak at gmail.com>
Cc: "Elecraft at mailman.qth.net" <Elecraft at mailman.qth.net>
Subject: Re: [Elecraft] Powering a K3s from a battery?
Message-ID:
	<CAGfPUrh=j8OfirRXyXGiBvqGJ5X266KCByjVeScgD9JRnjgGUQ at mail.gmail.com>
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I run /P on a 35aH lead acid battery. Whilst there is a noticeable voltage
drop, I have worked dx till the battery voltage falls well below 11v
without any noticeable effects on signal quality (I asked)!
I have also run from a battery in the shack with a charger connected. No
problem.

Clearly the larger the battery,  the less problems you will have.

GL and 73
John, C6ATS

On Tue, 29 Dec 2015 15:43 Marc Veeneman <mhvnmn at gmail.com> wrote:

> My K3/P3/VGA monitor are happy with power from
>
http://bioennodepot.com/lithium-iron-phosphate-lifepo4-batteries/bioenno-pow
er-12v-40ah-lfp-battery-pvc-blf-1240w.html
>
> It's small enough to lie flat on a shelf with 3.5" clearance with a
> footprint smaller than my iPad.
>
> My KX3/PX3/KXPA100 run on another identical battery.  These have plenty of
> capacity to power 100 watts CW for longer than I can stay active.  They
> start out at 13.2 volts and stay there for hours.  I do use #10 AWG wire,
> though, to minimize resistive loss.
> --
> Marc W8SDG
>
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