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Elecraft KX-1
A battery comparison chart has been added to
the bottom of this page. See also on my
Batteries & QRP page for more info on batteries and how
the tests were conducted.
Spectrum Analysis
 The
following plots were taken with a recently-calibrated Hewlett-Packard
HP-8563A spectrum analyzer. I am uncertain how much variation
there may be from one KX-1 to the next given the fact that different
builders may have different techniques with such tasks as winding
toroids and making clean solder joints. These plots represent
my own KX-1 and may or may not be typical of others. The built-in
auto-tuner was, of course, disabled for these tests.
Values below represent decibels below carrier.
Click on the thumbnail for a larger version of each band's plot.
| Plot |
Fundamental |
2nd |
3rd |
4th |
5th |
| |
7.0 MHz |
-40 |
-53 |
-60 |
-66 |
| |
10.1 MHz |
-35 |
-63 |
-71 |
-68 |
| |
14.0 MHz |
-58 |
-60 |
-73 |
-70 |
Two Ways to Power Your KX1 with 12V from an
Internal Battery
The portable KX1 operator faces a choice: the
simplicity and compactness of using 6 internal AA cells with
the resulting reduced output power caused by this 9V supply
or an external 12V battery pack that will power the KX1 to its
full potential.
I always made the latter choice when operating
afield with the rationale being that I would likely be using
a compromise antenna, shorter and lower than I'd prefer or have
available at home - therefore, I wanted every milliwatt I could
get. But I never liked having to attach an external battery
pack to the rig as this seemed to "undo" one of the
features I like best about the KX1 - its integrated portability.
1. As my external battery-pack-of-choice
evolved from alkalines to NiMh and finally to Lithium-Polymer
batteries (and as my LiPo collection grew), I found that a particular
3-cell (12V) 900 mAh would fit in each side of my KX1's bottom
case - exactly where the AA holders are normally mounted. So
I ordered an additional bottom case and the appropriate power
connector from Elecraft and one more 900 mAh LiPo battery and
wired them in parallel for 1800 mAh of capacity.
The results are:
- Preserved integration of the KX1
- Full power out of the KX1 for the duration
of the battery's charge (over 5 hours)
Yes, there are caveats associated with lithium-based
rechargeable batteries but I have them in my laptop and my cell
phone and see no reason not to put their advantages to use in
a QRP rig for the same reasons they are used elsewhere. I don't
leave this bottom case on the KX1 when I'm not actually in the
field with it and I also don't charge the batteries while this
case is attached to the rest of the rig.
The chart below summarizes the difference between
batteries:
This chart illustrates the difference between
the "best case scenario" with internal AA cells by
plotting high-powered lithium batteries against the 2-pack LiPo
batteries shown in the photo. Alkaline AA cells would fare even
worse and NiMH would be worse still.
Lifetime of these two types of batteries is
similar - the main difference is that the LiPos will provide
full power out of the KX1 for the duration of their charge whereas
the lower voltage provided by the 6 AA cells will not allow
the rig to operate to its full potential. Also note that the
starting voltage of the AA cells is less than what I consider
to be the end-of-charge voltage for the LiPo batteries.
Keep in mind that this plot is based on a constant
current draw of 300 mA. This is done for comparison purposes;
both batteries would typically last longer in actual QRP use.
2. A simpler way to have an
internal 12V battery in the KX1 utilizes both of the rig's existing
3xAA holders. At least one company, BatterySpace.com,
sells rechargeable Li-Ion batteries in an AA-size form factor.
These batteries have 3.7V each rather than the typical 1.2 to
1.5 volts for NiMH or alkaline batteries.
If the KX1's two battery holders were re-wired
so that they were in parallel with each other rather than in
series, six of these batteries would provide 12V with 1500 mAh
of capacity.
Cermark
900 mAh LiPo | N7CEE's
KX-1 Experiences | KX-1
Cheat Sheets | K6DGW's
KX-1
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