[Elecraft] K2: maximizing RF output, upping audio output.

[Don Wilhelm]

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?
>