[K3] TUNE function + external tuner + high SWR power reduction?

[Tim Tucker]

I just got an MFJ-998 auto tuner to work with the K3.  I'm using the K3 TUNE
function (15 watts) to trigger the auto tune function on the MFJ-998.
Generally, it works fine.  However, if I try to tune up to a very
non-resonant band on my antennas where the SWR is very high, the K3 reduces
the power output to the point where the 998 cannot initiate the tuning
process.  For example, if I try to load up an 80m dipole on 60m, the 998
gives an "increase power" response.  I can kick start the 998 into its
tuning process by manually changing inductance or capacitance values until
the K3 starts to increase the power output, at which point the 998 loads up
the antenna, but that is not really the way the whole process is supposed to
work.

In the example I gave above, the SWR reported by the K3 was around 9:1 for
the frequency I was trying to load up.  If the K3 TUNE is set to 15 watts,
how much power is actually being output when the rig sees 9:1 SWR?  Is there
a way to get the K3 to at least output 5 watts under a very high SWR
condition so that an external tuner can do it's job?   If I was just using a
random wire antenna, it's impossible to know what the inital SWR will be,
and it could be very high.  However, the tuner still needs 5 watts to
initiate the tuning process.

What am I missing?
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[Tony Estep]

On Tue, Sep 20, 2011 at 11:47 AM, Tim Tucker <[hidden email]> wrote:

> ...if I try to tune up to a very non-resonant band on my antennas where the
> SWR is very high, the K3 reduces
> the power output to the point where the 998 cannot initiate...

===============
Tim, there's no magic solution to this situation, but it's not hard to work
around it. The idea is to get the 998 in a state where it's not so far from
the solution. For example, if I switch from 20M to 80M, I get the result you
describe, but if I tune up on 40M and then go to 80M, all is well. A more
straightforward way is to push the C-Up or L-Up buttons until you get the
tuner to a better state, then press Tune on the K3 and then Tune on the 998.
When the 998 is in tune, you can set the display to show the L-C
combination, so this will give you a guide for what to do with C-Up and
L-Up. You just have to get somewhere in a very big ballpark to get the 998
to do its job. All in all, it's an excellent tuner that came out on top in
the ARRL's tuner comparison. Phil, AD5X, has some tips on this tuner on his
excellent website.

73,
Tony KT0NY



--
http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352
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[Phil Salas]

"I just got an MFJ-998 auto tuner to work with the K3.  I'm using the K3
TUNE
function (15 watts) to trigger the auto tune function on the MFJ-998.
Generally, it works fine.  However, if I try to tune up to a very
non-resonant band on my antennas where the SWR is very high, the K3 reduces
the power output to the point where the 998 cannot initiate the tuning
process..."

Usually the problem is due to you having a tuning solution on one band that
leaves a very high SWR when you move to a new band - often worse than if the
MFJ-998 was just bypassed (the MFJ-998 doesn't "know" you've changed bands
except by sampling RF).  The solution is usually to just tap the TUNE button
on the MFJ-998 when you change bands.  This bypasses the tuner.  Then hit
TUNE on the K3.  In most cases there will be enough power to start the tune
cycle on the MFJ-998.

Phil - AD5X

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