Allan,
You have received several replies, and most (if not all) said "don't do
that".
I recommend that you keep the power on the K2 to 10 watts or less - that
is the design point. Above that, the IMD increases and the components
are stressed more than at the 10 watt level. Furthermore, the PA
efficiency decreases when the design point is exceeded.
If you need additional power at times, I suggest you add an amplifier -
either the KPA100 or something like the HFPacker amp.
The KPA100 is ideal and can provide both low power and high power
operation. You can power the base K2 from the coaxial power jack and
operate at 10 watts or less, and if there is a power source connected to
the KPA100, operation at 11 watts and above is just a matter of turning
the power knob. Should the power to the KPA100 go down, you still have
power to the base K2 (assuming a battery supply on the base K2) and
operation can continue at 10 watts or less. The KPA100/K2 is designed
for this type of operation and the switchover is instantaneous and
automatic.
Since you are mostly concerned with emergency communications, this seems
to me to be the best solution - operate the base K2 on a gel cell
battery, and operate the KPA100 from an AC source or automotive (or
other large capacity) battery. If the KPA100 power fails, you can still
communicate, but at lower power.
That is a lot safer than trying to "hot rod" your QRP K2 which could
lead to failure. Murphy strikes at times when the needs are the
greatest - don't try to defy Murphy, you could be left without any
communications capability.
As for the audio, it is normally sufficient for headphones or on speaker
in a normal room environment (for those with normal hearing). If you
are operating with a speaker in a high ambient noise situation, the best
solution is to use an external audio amplifier.
73,
Don W3FPR
On 9/26/2013 8:55 AM, Allan Taylor wrote:
I have a very early K2 that I use for field operations. It functions as an
emergency communication source for serious
backcountry trips (multi-day wilderness whitewater rafting, etc.). I am
finding that a power output of, say, 20W would be
desirable as a compromise between more reliable communication and battery
usage. My K2 puts out about 14W. Thus I
ask the experts: has anyone revamped the TX RF stages sufficient to put out
20 -25W output? Yes, I know this amounts
to only a dB or two. But it can be the edge needed in very marginal
conditions.
Second issue. The K2 has always been on the low side for RX audio. Being no
longer a young buck, my hearing is not
perfect any more. Is there a known mod to add 5-10 dB to the audio chain
without drastic distortion? Presently I take along
a Radio Shack headphone 3-way amp that gives about that. It works fine but
is yet another piece of gear to bring along and
doesn't feed the internal speaker. When I had a KX1 (now sold) it had been
modified to have a second audio amp chip put
in and it really helped. Has anyone done a similar thing for the K2? I am
not a EE by any means so would prefer to follow
known modification paths.
Anyone?
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