8
Switch to 30 meters and align the two trimmers on the KXB30. You can peak them while listening to
WWV at 10 MHz, or using signals or noise in the ham band (10100-10150). The peak of either or both
capacitors may be somewhat broad since they represent only a portion of the total capacitance.
i
C1 and C2 on the KXB30 are switched in on 30 meters, and also when you tune below 6.7 MHz
(approx.) on 40 meters. This re-peaks the receive band-pass filter near the center of the 49-meter SWL band
(about 6.1 MHz), greatly improving sensitivity in this band. The following step will confirm this.
Switch to 40 meters and tune the VFO down toward the midpoint of the 49-meter SWL segment
(about 5.9-6.2 MHz). Locate a signal in this vicinity. If the KXB30 was properly aligned, it will now be
greatly enhancing sensitivity in this range. Next, temporarily set the
B 3 0
parameter to
O F F
, then exit the
menu. As soon as you move the VFO, sensitivity should drop sharply. Re-set the
B 3 0
parameter to
O N
and exit the menu. Sensitivity should increase again.
Turn off the KX1 and re-install the bottom cover.
Be very careful not to pinch the battery wires
between the bottom cover and the ATU module or the nearby long standoff.
Circuit Details
When the KX1 is switched to 30 meters (or tuned below about 6.7 MHz on 40 meters), the MCU places 5
volts DC on point
D
, forward biasing high-performance PIN diodes D1 and D2. This inserts the series
combination of C3/C1 in parallel with points
A
and
B
, i.e. in parallel with CA on the KX1; it also inserts C2
from point
C
to RF ground, or across L7 on the KX1. At other times point
D
is at 0 volts, reverse biasing
the diodes so they have a minimal effect on the band-pass filter.
C1
C3
68
40
L1
W. Burdick
Elecraft
E.Swartz
Rev.
Sht.
Date
By
1 of 1
D1
P I N
47µH
A
10/11/03
K
K
K
KX
X
X
XB
B
B
B3
3
3
30
0
0
0 3
3
3
30
0
0
0----m
m
m
m M
M
M
Mo
o
o
od
d
d
du
u
u
ulllle
e
e
e
L2
47µH
L3
47µH
D2
P I N
C2
40
C4
0.1
C5
0.1
R 5
R 4
B
A
G
C
5
D
G
1K
1K
*
*
*
*
L1-L3 may be labeled R1-R3 on the PC board
5V ON, 0V OFF
5V
4V ON, 2.5V OFF
