[K2] Tuning a magloop with KAT100

[Brian - N5BCN]

I've recently acquired a magloop that will be used with a K2/KPA100/KAT100 and I wanted to double check my tuning procedure.

My plan was to tune the KAT100 into a dummy load (ATU in AUTO mode) and then place the ATU into SWR (x.x-1) mode.  Then use the TUNE button on the K2 to tune the loop to resonance, then operate.  Repeat for any band changes or when encountering significant SWR.

Does this sound reasonable or am I missing a step or two?

Brian, N5BCN

[Don Wilhelm-4]

Brian,

There is no need to tune into a dummy load first.  When the ATU menu is
set to CAL, the L and C elements in the KAT100 are bypassed.
There may be some residual L and C in the PC traces and relay contacts,
but that should be minimal.
Yes, you can use the TUNE button and observe the SWR on the K2 as you
tune the loop.

Be aware that the TUNE with the KPA100 in-line and powered will be at 20
watts unless you set the power knob to a lower level.

73,
Don W3FPR

On 11/30/2015 2:20 PM, Brian - N5BCN via Elecraft wrote:
> I've recently acquired a magloop that will be used with a K2/KPA100/KAT100
> and I wanted to double check my tuning procedure.
>
> My plan was to tune the KAT100 into a dummy load (ATU in AUTO mode) and then
> place the ATU into SWR (x.x-1) mode.  Then use the TUNE button on the K2 to
> tune the loop to resonance, then operate.  Repeat for any band changes or
> when encountering significant SWR.
>
>

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[Rick WA6NHC-2]

Brian,

Magloops have a VERY narrow bandwidth and putting RF power into them can
cause significant damage if the ANTENNA is not tuned.  Plus you'd be
experiencing significant line loss on your feed if the SWR wasn't
right.  That's two major drawbacks of your plan.

I would suggest that bypassing the KAT100 and tuning only with the
controls for the magloop is a far better way to go.  A mistuned magloop
will also show substantial  LOSS at the desired frequency so all tuning
should happen at the antenna for best operations.  First peak the
receiver noise as you adjust the antenna controls, then apply only
enough power to get a response from the SWR meter (say 5-10 watts); fine
tune the antenna controls for a good match.  Do NOT use the tuner in the
radio.

I was given one, have tried it and frankly I'm unimpressed with the
operation and performance.  I was hoping for better as it would make a
nice RV antenna, but a dipole works MUCH better.  If it is all one can
manage (HOA or lot limitations), it works but it is so narrow that
typical S&P ops are rather challenging, you're never tuned for that new
frequency.  As one that changes bands often and quickly, it would
severely hamper how I operate.  Tuning requires patience and time on the
lower bands, even a 20 KHz frequency change requires retuning.

But the bottom line is that in this case you must tune the ANTENNA, not
match it externally.  Good luck!

73,
Rick wa6nhc

On 11/30/2015 11:20 AM, Brian - N5BCN via Elecraft wrote:

> I've recently acquired a magloop that will be used with a K2/KPA100/KAT100
> and I wanted to double check my tuning procedure.
>
> My plan was to tune the KAT100 into a dummy load (ATU in AUTO mode) and then
> place the ATU into SWR (x.x-1) mode.  Then use the TUNE button on the K2 to
> tune the loop to resonance, then operate.  Repeat for any band changes or
> when encountering significant SWR.
>
> Does this sound reasonable or am I missing a step or two?
>
> Brian, N5BCN
>

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[Bill Frantz]

I had the same experience with the Little Tarheel II on my
4Runner. I was running S&P on 80 meters and as I swept the band,
every time I sent my call to a new station, I was also peaking
up the antenna tuning.

There's a nice article in the latest QEX on automatically tuning
these kinds of antennas. "Using an Arduino to Automatically Tune
an MFJ-1788 Magnetic Loop Antenna and Elecraft KX3 Transceiver"
Elwood Downey, WB0OEW (November-December, 2015).

73 Bill AE6JV

On 11/30/15 at 11:35 AM, [hidden email] (Rick WA6NHC) wrote:

>... is so narrow that typical S&P ops are rather challenging,
>you're never tuned for that new frequency.  As one that changes
>bands often and quickly, it would severely hamper how I
>operate.  Tuning requires patience and time on the lower bands,
>even a 20 KHz frequency change requires retuning.
-----------------------------------------------------------------------
Bill Frantz        | gets() remains as a monument | Periwinkle
[phone]      | to C's continuing support of | 16345
Englewood Ave
www.pwpconsult.com | buffer overruns.             | Los Gatos,
CA 95032

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[Rick WA6NHC-2]

Yup, I can relate to that too.  For exactly the same reason, it is a
highly compromised miniature antenna.  I have the model 100 on my
truck.  But I keep a manual tuner and all band dipole with feed lines
and a CCM in the RV... except most of the time the trees are too short
to be of value.  :-\

Rick nhc

On 11/30/2015 3:46 PM, Bill Frantz wrote:

> I had the same experience with the Little Tarheel II on my 4Runner. I
> was running S&P on 80 meters and as I swept the band, every time I
> sent my call to a new station, I was also peaking up the antenna tuning.
>
> There's a nice article in the latest QEX on automatically tuning these
> kinds of antennas. "Using an Arduino to Automatically Tune an MFJ-1788
> Magnetic Loop Antenna and Elecraft KX3 Transceiver" Elwood Downey,
> WB0OEW (November-December, 2015).
>
> 73 Bill AE6JV
>
> On 11/30/15 at 11:35 AM, [hidden email] (Rick WA6NHC) wrote:
>
>> ... is so narrow that typical S&P ops are rather challenging, you're
>> never tuned for that new frequency.  As one that changes bands often
>> and quickly, it would severely hamper how I operate.  Tuning requires
>> patience and time on the lower bands, even a 20 KHz frequency change
>> requires retuning.
> -----------------------------------------------------------------------
> Bill Frantz        | gets() remains as a monument | Periwinkle
> [phone]      | to C's continuing support of | 16345 Englewood Ave
> www.pwpconsult.com | buffer overruns.             | Los Gatos, CA 95032
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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