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K2: maximizing RF output, upping audio output.

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Allan Taylor

K2: maximizing RF output, upping audio output.

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?

--
73 Allan K7GT
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Vic Rosenthal

Re: K2: maximizing RF output, upping audio output.

Before the KPA100 came out I experimented with the K2 to see if I could get more output to
drive an external amplifier.

There IS a way, but I am sure there are lots of dangers involved. I will say that I did
this for a month or so until I got my KPA100. I am not recommending it!

The K2 has a closed-loop power control circuit. The MCU looks at the amount of power being
produced and adjusts the drive to increase or decrease it until it matches the setting of
the POWER control.

So if you lie to the MCU and tell it that less power is coming out than actually is, it
will increase the drive to try to make it reach the set point.

I have a KAT2 so all I had to do was adjust the forward power pot to say that there was
less output. I believe I got about 22 watts on 40 meters this way (less on other bands).

Again, you are undoubtedly stressing things beyond design limits when you do this and bad
things could happen. It might be better to get an external amplifier like the HF Packers use.

On 9/26/2013 5:55 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?
>

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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EricJ-2

Re: K2: maximizing RF output, upping audio output.

In reply to this post by Allan Taylor

Far more importantfor emergency communication is a reliable radio with
over a decade of testing behind it...you already have that. If you are
depending on SSB, you would be better off bringing along a key than
installing someones favoritepower tweak. Or look into SPOT gps and leave
the K2 at home.

http://www.findmespot.com/en/

Eric
KE6US

On 9/26/2013 5:55 AM, Allan Taylor wrote:

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k6dgw

Re: K2: maximizing RF output, upping audio output.

In reply to this post by Allan Taylor

On 9/26/2013 5:55 AM, Allan Taylor wrote:

> Yes, I know this amounts
> to only a dB or two. But it can be the edge needed in very marginal
> conditions.

Sounds like quite a bit of effort for 1.155dB.
>
> Second issue. The K2 has always been on the low side for RX audio.

Same problem for me and on KX1 too. I found a little AF distribution
amp at RS, plugs into the headfone jack and has 3 outputs. Runs on a
couple of AA batteries, seemingly forever. Seems to have about 15dB of
gain. I also found some RS ear buds that say "Koss" on them and they're
noticeably more sensitive. The combo doesn't really fix it for me
[nearly deaf], but it sure helps.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2013 Cal QSO Party 5-6 Oct 2013
- www.cqp.org

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Don Wilhelm-4

Re: K2: maximizing RF output, upping audio output.

In reply to this post by Allan Taylor

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:

w7aqk

Re: K2: maximizing RF output, upping audio output.

In reply to this post by Allan Taylor

Ron and All,

I think Ron's cautionary comments are right on! I remember a number of
years back when the Kenwood TS-50 first came out. It didn't take long for
the "tinkerers" to realize that the output transistors in that rig were very
conservatively rated. It was often stated that they could probably run as
much as two or three times the rating for the rig (100 watts). Sure enough,
a bunch of folks started "hopping up" their TS-50's. Problem is, most of
them forgot all about whether or not the output filters could handle that
much extra power. Apparently they couldn't, because soon you started
hearing a lot of sad stories.

Beefing up a K2 beyond it's design capability seems like pure foolishness to
me--unless you want to basically redesign the whole rig! Besides, most 12
volt rigs have significant IMD issues when run much above the design limit.
It doesn't take much either. The K3 runs pretty well at 100 watts, but at
110 watts (which is would do initially) it started getting dirty. I think
they subsequently capped it at 100 watts via firmware.

A few more watts just isn't worth it---usually! If you want to boost your
power, get an amp--even a small one. Or build one--there are a bunch of
good designs around for simple and inexpensive amps . Why jeopardize a
great rig like a K2 for a few more watts?

Dave W7AQK

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