Elecraft KAT1 Manual - Manual (Page 15)

Elecraft • www.elecraft.com • 831-662-8345
Circuit Details
The ATU uses four inductors and five capacitors in an L-network. The capacitance can be placed at the transmitter or
antenna end of the network via K5. Each inductor and capacitor has its own DPDT relay, with the individual sections of
each relay placed in parallel for reliability. The relays are selected under control of the ATU's microcontroller, U1.
Latching relays are used so that they will not consume any power except when the operator is actually tuning.
T1, D1, D2 (etc.) form a directional coupler for SWR and power measurements. The bridge output is buffered by op-
amp U2 and routed to the K1 control board. The bridge outputs are also connected to A-to-D inputs on the
microcontroller, U1. U1 measures these voltages and converts them to SWR or power readings, using averaging and
linearization techniques to improve accuracy. During normal operation, the RFDET/DATA line provides an analog
power indication to the K1’s main microcontroller. When SWR is to be displayed, this line is used to transmit digital
SWR data (10 ms/bit data rate). U1 "sleeps" except during antenna tune-up, so it generates no receiver noise.
KAT1 Schematic
W. Burdick
E. Swartz
Elecraft
2.6µH
Rev. Sht.
.32µH .64µH 1.3µH
Date
M M M MCC C CUU U U
150
B y
L1 L2
K2
L3 L4
C1 C2 C3 C4 C5
10 22 39 82
2 4
3
9 7
8
5-30pF
1N5711 1N5711
3.3K
C9
C10
C11 C12
100
.001 .001
200
100K
R 3 D1 D2
R 4
R 2 R 1
T1
4
2
3
1
6 5
10
1 2
3 4
5 6
7 8
9
P2
RF IN
RF OUT
PIC16C72
MCLR OSC1 OSC2 RA4 RC0 RC1 RA0 RA1 RA2 RA3 RA5 VSS RC2 RC3
RC4 RC5 RC6 RC7 VSS VDD RB0 RB1 RB3 RB4 RB5 RB6 RB7 RB2
10 14
15 20 25 28
U U U U 11 1 1
1 5
K10
10
1
K5 K4 K3 K2 K1 K6 K7 K8 K9
4.0MHz
Z1
.047
C15
100
R 5
P1
12
3
REFL
FWD
C16
.01
KAT1 Antenna Tuner
1 of 1 A
1K
R 6
6A
L-NETWORK SELECT
L1-L4 use T37-2 cores
FT37-43
.001
C17
NULL ADJ.
REFL
K5
2 4
3
9 7
8
C TX
K1
2 4
3
9 7
8
K3
2 4
3
9 7
8
K4
2 4
3
9 7
8
2
4
3
9
7
8
K6
2
4
3
9
7
8
K7
2
4
3
9
7
8
K8
2
4
3
9
7
8
K9
2
4
3
9
7
8
K10
C ANT
5
6
7 +
-
U2B
REFL
DATA
RFC1
100 µH
6R/AUX
8t, 12t, 17t, 25t
3
2
1 +
-
8
4
U2A
6A
To Filter Board, J1
To Filter Board, J2
D3
1N34A
LM358
DATA
FWD
= On bottom of PC board.
TT T T PPPP 11 1 1
N N N NO O O OTT T TEEEESSSS::::
1. R36 on the K1 RF board must be removed when the ATU is installed (see text).
11-27-00
Pins 5 and 6 of each relay are used as tie points but are not internally connected.
2. K1-K10 are single-coil latching relays, shown in the RESET position.
.001
C13
.001
C14
FWD
RFDET/DATA