Antenna?

[Doug Forman]

Okay, this is a follow-up to my KX1 antenna question posted last night.  
I came home tonight and did a bunch more measurements.

====================

First, grouped by antenna:

Cushcraft MA5V "Mini Vertical"
40m:  7055 - (tuner in - 2.1 Watts out, SWR 1.1 ) - (tuner out - 1.4
Watts out, SWR 5.7) - MFJ-259B: SWR 7.6
30m:  10107 - (tuner in - 4.3 Watts out, SWR 5.6) - (tuner out - 6.3
Watts out, SWR 9.9) - MFJ-259B: SWR 6.5
20m:  14065 - (tuner in - 2.1 Watts out, SWR 1.0 ) - (tuner out - 2.5
Watts out, SWR 1.0) - MFJ-259B: SWR 1.1

Slinky Dipole "CliffDweller II"
40m:  7055 - (tuner in - 2.1 Watts out, SWR 1.0) - (tuner out - 2.0
Watts out, SWR 1.3) - MFJ-259B: SWR 1.6
30m:  10107 - (tuner in - 1.8 Watts out, SWR 5.2) - (tuner out - 1.8
Watts out, SWR 7.0) - MFJ-259B: SWR 8.4
20m:  14065 - (tuner in - 3.0 Watts out, SWR 1.2) - (tuner out - 1.4
Watts out, SWR 8.0) - MFJ-259B: SWR 8.8

Dummy Load (Oil-filled "Can-tenna")
40m:  7055 - (tuner in - 2.9 Watts out, SWR 1.0) - (tuner out - 2.2
Watts out, SWR 1.0)
30m:  10107 - (tuner in - 2.3 Watts out, SWR 1.0) - (tuner out - 2.5
Watts out, SWR 1.0)
20m:  14065 - (tuner in - 2.3 Watts out, SWR 1.0) - (tuner out - 2.0
Watts out, SWR 1.0)

====================

Second, grouped by band:

40 meters (7055)
MA5V Vertical - (tuner in - 2.1 Watts out, SWR 1.1 ) - (tuner out - 1.4
Watts out, SWR 5.7) - MFJ-259B: SWR 7.6
Slinky Dipole - (tuner in - 2.1 Watts out, SWR 1.0) - (tuner out - 2.0
Watts out, SWR 1.3) - MFJ-259B: SWR 1.6
Dummy Load - (tuner in - 2.9 Watts out, SWR 1.0) - (tuner out - 2.2
Watts out, SWR 1.0)

30 meters (10107)
MA5V Vertical - (tuner in - 4.3 Watts out, SWR 5.6) - (tuner out - 6.3
Watts out, SWR 9.9) - MFJ-259B: SWR 6.5
Slinky Dipole - (tuner in - 1.8 Watts out, SWR 5.2) - (tuner out - 1.8
Watts out, SWR 7.0) - MFJ-259B: SWR 8.4
Dummy Load - (tuner in - 2.3 Watts out, SWR 1.0) - (tuner out - 2.5
Watts out, SWR 1.0)

20 meters (14065)
MA5V Vertical - (tuner in - 2.1 Watts out, SWR 1.0 ) - (tuner out - 2.5
Watts out, SWR 1.0) - MFJ-259B: SWR 1.1
Slinky Dipole - (tuner in - 3.0 Watts out, SWR 1.2) - (tuner out - 1.4
Watts out, SWR 8.0) - MFJ-259B: SWR 8.8
Dummy Load - (tuner in - 2.3 Watts out, SWR 1.0) - (tuner out - 2.0
Watts out, SWR 1.0)

====================

Notes:

1.  KX1 #731 with 30m and Antenna Tuner installed, running from
batteries only, Lithium, 8.9v indicated.  All power out and SWR
indications from the KX1 except as noted from the MFJ-259B.

2.  SWR Analyzer is MFJ-259B

3.  MA5V Vertical is tuned for digital modes, so SWR measurements of 1.0
and 1.1 are expected.

Observations:

1.  KX1's antenna tuner does a fantastic job matching either antenna on
40 meters.

2.  KX1's antenna tuner does a dismal job matching either antenna on 30
meters.

3.  KX1's antenna tuner does a fantastic job matching the slinky dipole
on 20 meters.
    (vertical is already resonant on 20m)

I guess it's just interesting to me that the internal tuner does such a
GREAT job matching the 135' slinky dipole on both 20 and 40 meters, but
falls apart on 30meters.  It's also interesting to me that the internal
tuner NICELY matches the MA5V on 40 meters (it's only a 10-20m vertical
with a SWR of 7.6 on the antenna analyzer at 7055khz).

I appreciate the suggestions I have received so far and will check them
out - first by adjusting the coax length by adding some to see if the 30
meter situation improves (without negatively affecting 20/40 meters).  
Any other observations or suggestions are welcome!

72's,

Doug  N7BNT




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[wayne burdick]

On Jul 7, 2004, at 10:16 PM, Doug Forman wrote:

> I guess it's just interesting to me that the internal tuner does such
> a GREAT job matching the 135' slinky dipole on both 20 and 40 meters,
> but falls apart on 30 meters.  It's also interesting to me that the
> internal tuner NICELY matches the MA5V on 40 meters (it's only a
> 10-20m vertical with a SWR of 7.6 on the antenna analyzer at 7055khz).

Hi Doug,

The KXAT1 was designed with medium-length random wires in mind. It has
a fairly limited Z-matching range, and may have a rough time with very
low-Z or high-Z loads. In your case, the L and C values provided just
happened to hit a sweet spot on the Smith chart with your 40-meter
tuneup on the vertical. And a sour spot on 30 with the slinky dipole  
;)  The L and C steps are fairly coarse, so with loads like this, it
will be hit-or-miss.

If you want to make sure the KXAT1 is working as intended, try the
"sorta-vertical" we recommended in the KXAT1 manual: toss about 20 to
25' of wire into a tree, and lay out a 16' radial on the ground. The
L/C values were tuned for this easy-to-erect field antenna.

The ATU also does a great job with not-quite-resonant antennas.
Example: the Maldol AH-14 20-meter whip. This whip is tuned for the
high end of the band, but the ATU finds a match close to 1.0:1, making
the transmitter happier. Without it, the SWR is over 3:1.

73,
Wayne

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[Larry Kayser]

Greetings:

The limited tuning range of the KXAT1 antenna tuner originally bothered
me some.  Since I started working with it, and I am still having a few
problems with the unit but that is another story, I have experimented
with a simple technique to deal with very short or wires approaching 1/2
wave long.  I am not keen to measure the length of wires that I toss
into a tree, so I have taken to carrying a small coil with me that I
just put in series with the random wire if the ATU is unable to achieve
a reasonable SWR.  The action is to simply move the effective length of
the wire along a ways, thus avoiding the 1/2 wave length of wire.  This
could also be done with a small capacitor, but I have not yet taken one
of these in my pocket when I go for a walk to the back of my island home.

The coil I use is about 30 turns on a 1r5 inch form, spaced one wire
diameter.  I have never worked out the inductance, it was left over from
a receiver experiment some years ago.

Larry
VA3LK



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[Stuart Rohre]

Doug,
Hams have to remember, even if using coax, with a tuner on the rig, the coax
is part of the antenna system and can radiate if a critical length.  This is
obviously why the 30m band is hard to match.  You have to make the antenna
plus coax of an electrical length the tuner can match.

GL and 72,
Stuart
K5KVH


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