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

Thu Sep 26 21:52:02 EDT 2013

And you have another "QRO" option available soon: The KXPA100 100 watt amp.
Although designed to integrate very closely with the KX3, it is a great
general purpose 100 watt amplifier for use with almost any 160-6 meter rig.
It needs about 5 watts of drive to produce 100 watts output. 

Of course, the KPA100 is "internal" to the K2, replacing the top cover if
you want the most compact possible combination, but the KPA100 does not
include an internal automatic antenna tuning unit (ATU). Elecraft has the
KAT100 ATU for that purpose. An ATU can be invaluable in field emergency
operations. The KXPA100 has that option inside its box so, if you want 100
watts with an ATU, either solution does it with two boxes. 

Like Fred, I learned about equipment performance curves as an aircraft
pilot. I'm happy to say that I have never broken an airplane (which is
probably why I'm alive to write this) nor a piece of equipment through
pushing things beyond the red line. Some might call me a wimp, but this
wimp's equipment is reliable.

I hope you can find the reason for the low audio. Be sure BOTH the AF and RF
gain controls are turned up. I stand behind my earlier suggestion to check
the speaker wiring. Those who managed to reverse the connector and short the
audio line (fairly easy to do) often reported weak, low-level audio rather
than no audio at all. It would be great if that was all that was the matter
with your K2's audio.  

73, Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Wilhelm
Sent: Thursday, September 26, 2013 5:22 PM
To: Allan Taylor
Cc: Elecraft
Subject: Re: [Elecraft] K2: maximizing RF output, upping audio output.

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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