K2: MARS Frequency Access?

[Jon Perelstein]

Is the K2 a viable radio for MARS work?  I found some references in
the archives from back in 2005 suggesting that it won't transmit on
some of the MARS frequencies even though it appears to be transmitting
on them -- the VFO display shows the desired frequency, but that far
out of band it's not transmitting on the frequency it's displaying.
The issue appeared to be one of how far out of band the PLL will go,
as opposed to there being a restriction programmed into the
microprocessor.

I confirmed last night that mine (#6550) will not -- on some of the
bands -- transmit as far out of band as needed, even though it is
transmitting.

There was no mention in that exchange of any mods that might be done
to make the K2 capable of transmitting on the MARS bands, and I
haven't found any other useful posts on the subject.

Has anyone successfully modified a K2 for MARS operations, and if so
what did you do.

73s
Jon
WB2RYV

P.S.  If you respond with the old "well tell us what the MARS
frequencies are so we can answer the question" response, it means that
you haven't modified a K2 to do what I need and therefore don't have
the information I need.
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[Mike Morrow-3]

> P.S.  If you respond with the old "well tell us what the MARS
> frequencies are so we can answer the question" response, it means that
> you haven't modified a K2 to do what I need and therefore don't have
> the information I need.

I like your attitude.  I can tell that you really know how to motivate
folks to help you.  But of course, just between you and me, we *know* that
questions like that are really only tricks to gain knowledge of highly
classified MARS frequencies so that Red China, Russia, and Al Qaeda can
monitor the very 'sensitive' traffic found there.  :-)

In point of fact, most popular (commonly-used) HF MARS frequencies for
Navy-Marine Corps MARS and Army MARS will likely fall within K2 range.
You obviously are seeking operation on USAF MARS frequencies, most of
which are well outside K2 operating capability.  (I hope that isn't
revealing too much classified information.)  So...in fact, some indication
of what frequencies are to be used would be important to someone attempting
to help you.  Imagine that!

73,
Mike / KK5F
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[Don Wilhelm-4]

Jon,

How far out of the ham bands you can go with the K2 depends on 3 factors.
First is the range of the VFO tuning.  If you measure the PLL/VFO range
at the left end of R30, but extend the voltage range  to 1.0 volts to
7.0 volts. and you will have an indication of how far out of band the
VFO will tune.  Beyond those points, the VFO indication on the display
will not be reliable.
The second is the falloff of the bandpass filter.  That can sometimes be
modified slightly by tuning at a different frequency than is indicated
in the K2 manual.  For instance, if you need to tune up to 4300 kHz, you
may be able to shift the bandpass filter tuning by setting the frequency
to  3900 instead of 3750 when tuning the 80 meter bandpass filter.  The
response falloff at the edges of the new "BAND" limits should be checked.
The 3rd thing is the Low Pass Filters.  Remember there are 2 sets in the
K2/100 - one in the base K2 and another in the KPA100.  The bands that
they cover are not necessarily the same.  For instance, the base K2 LPF
combines 30 and 20 meters, so if you want to transmit at 12 MHz, that
one will give you no problem, but the 40/30 meter LPF in the KPA100 is
designed to cut off the 2nd harmonic of 60 meters, so it has a rather
steep cutoff after 11 MHz, so attempting to run a 12 MHz signal through
that filter will likely result in low output and high current drawn by
the KPA100 and there is a liklyhood of damage.

Bottom line - unless the MARs frequencies are quite close to the ham
bands, the K2 will not do the job.  It could be modified for the MARs
frequencies, but it may not cover the entire span of the ham bands
afterward.  I would discourage such modification, and any mod to the VFO
Range Select is quite tricky (a change of a few pF makes a big change in
the range) and not all K2s will respond the same to any given capacitor
due to component tolerances.

So, yes, the K2 can be modified with a LOT of work, some of it requiring
redesign of the VFO, Bandpass Filter, and the Low Pass Filters.  When
you are done, it may or may not be usable on the ham bands.

I believe the K3 (with the KBPF3 option) and the KX3 are better
candidates for MARS operation.

73,
Don W3FPR

On 9/24/2012 11:34 AM, Jon Perelstein wrote:

> Is the K2 a viable radio for MARS work?  I found some references in
> the archives from back in 2005 suggesting that it won't transmit on
> some of the MARS frequencies even though it appears to be transmitting
> on them -- the VFO display shows the desired frequency, but that far
> out of band it's not transmitting on the frequency it's displaying.
> The issue appeared to be one of how far out of band the PLL will go,
> as opposed to there being a restriction programmed into the
> microprocessor.
>
> I confirmed last night that mine (#6550) will not -- on some of the
> bands -- transmit as far out of band as needed, even though it is
> transmitting.
>
> There was no mention in that exchange of any mods that might be done
> to make the K2 capable of transmitting on the MARS bands, and I
> haven't found any other useful posts on the subject.
>
> Has anyone successfully modified a K2 for MARS operations, and if so
> what did you do.
>

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[Jon Perelstein]

Thanks Don.

Definitely sounds like something I don't want to do.  Okay, which of
my kids do I sell to buy a K3?

73s
Jon
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