Automatic Band Decoder for the antenna switches or filters
February 2015
OK2ZI
Rev 1.0
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Introduction
The Automatic Band Decoder continuously decodes your transceiver's band changes and
provides a separate output for each of the nine bands of your rig. By connecting an external
antenna switch to the decoder's output, automatic and correct antenna selection is
accomplished.
The Band Decoder is primary designed for Yaesu radios with band output signal BCD coded
at TTL voltage levels.
However, it can be used with any other device that uses the same method of band coding at
TTL voltage levels (for example Microham MK2R or LPT computer port). Then the computer
running software may send the current band information to the computer's LPT port or to an
auxiliary output at Microham MK2R. Many computer logging programs support this feature
now, which can be useful if you have a Kenwood or Icom transceiver. Consult your
transceiver and software manuals on how to interface your radio to the computer and how
to enable the software's antenna control feature.
If you want to use an another kind of controller (like Arduino, RaspberryPI etc.), then the
different bands are coded as follows:
Binary code
0001
0010
0011
0100
0101
0110
0111
1000
1001
Band
160m
80m
40m
30m
20m
17m
15m
12m
10m
Table 1.
The Band Decoder provides source driver outputs, which provide a source of 12Vdc for the
“hot” side of external relays (common point for the relays is a ground or minus pole).
All of the antenna switches designed by OK2ZI are controlled by this way, but you can
control many other products with the same method of switching.
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Circuit Description
The schematic of the Band Decoder is shown in Figure 1.
Figure 1.
The decoder accepts a four bit binary-coded decimal (BCD) word at TTL levels and decodes it
at IC3 (a CMOS BCD-Decimal Decoder). Data Bit A is the Least Significant Bit (LSB) and Data
Bit D is the Most Significant Bit (MSB). All nine bands are decoded as described in Table 1.
The outputs of IC3 go high to reflect that band in use.
Four of the IC3 outputs are routed to IC1, five of the IC3 outputs are routed to IC2. IC1 and
IC2 contain eight N-channel Darlington pair transistor switches, see Figure 2.
Figure 2.
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All nine switches function in the same manner. When their input goes high, their output
switches high. All unselected outputs float at ground level if connected to the antenna
switch relays.
Please note: Output for 160m-15m bands are doubled, two outputs are connected together
for higher current output. Output current capability is min. 350mA per output, but the total
dissipation of whole IC must be kept under 2W. The average output Darlington pair
saturation voltage is 1.7V, therefore the power supply must deliver at least 13.7V for the
12V relays ! More information can be found in the datasheets for UDN2981 or TD62783.
The Band Decoder is powered through either the K6 terminal block or via the “data” cable
from the transceiver. Diodes D1 and D3 isolate these two sources to prevent circulating
currents in case voltage is applied to both inputs simultaneously. If the voltage drop 0.5V [at
the diode is significant for the function, you must use higher power supply voltage. 14-15V
should be enough for 12V relays. If you can’t use higher supply voltage than 13,8V then
remove the appropriate diode and substitute a wire bridge in its place. D2 is a protection
transient voltage suppression diode P6KE18A with the 18V clamping level for the protection
of the relays from overvoltage. If you want to optionally use 24V relays then replace D2 with
P6KE27A or with P6KE30A for 26V relays.
BCD decoder CMOS4028 is powered from 5V monolithic stabilizer IC4 – 78L05. Resistor
networks R5 and R7 with the capacitors C4-C7 are for EMI protection.
The Band Decoder can be connected to the transceiver via DIN8 connector K7 or via header
connector K8. The pinout of K7 is the same as on the YAESU transceivers.
Band data pinout at Yaesu DIN8 band data connector.
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Band data pinout at Yaesu Mini-DIN8 band data connector.
I don’t offer the cable between transceiver and the Band Decoder. For the transceivers with
the Mini-DIN8 you can buy standard Yaesu CT-58 cable, for the transceivers with the DIN8
search the Web and eBay. Those cables are available from other sellers.
The antenna switch relays are connected via K1-K5 terminal blocks. Do not forget to connect
also the power ground from K5.2.
Applications
With the Band Decoder you can control up to 9 separate relays one for each band.
Very often many Hams use multiband antennas and then less amount of relays are needed.
In this case you can combine the Band Decoder outputs in parallel.
Examples:
1. You have 4:1 antenna switch and 4 antennas, but only 2 are mono-band antennas.
Band
160m
80m
40m
30m
20m
17m
15m
12m
10m
Antenna
Dipole
Inverted Vee
40/30 GP
40/30 GP
5 band Yagi
5 band Yagi
5 band Yagi
5 band Yagi
5 band Yagi
4:1 Switch Port
1
2
3
3
4
4
4
4
4
Band Decoder combination
K1.1
K1.2
K2.1+K2.2
K2.1+K2.2
K3.1+K3.2+K4.1+K4.2+K5.1
K3.1+K3.2+K4.1+K4.2+K5.1
K3.1+K3.2+K4.1+K4.2+K5.1
K3.1+K3.2+K4.1+K4.2+K5.1
K3.1+K3.2+K4.1+K4.2+K5.1
The Band Decoder outputs can be combined at the PCB with short wires or at the terminal
block. See images.
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On board connection
Out of board connection
2. You have 6:1 antenna switch and 6 antennas, and 2 are multi-band antennas.
Band
160m
80m
40m
30m
20m
17m
15m
12m
10m
Antenna
160m Dipole
80m Inverted Vee
40m Ground Plane
30m Dipole
20m-15m-10m Yagi
17m-12m Yagi
20m-15m-10m Yagi
17m-12m Yagi
20m-15m-10m Yagi
6:1 Switch Port
1
2
3
4
5
6
5
6
5
Band Decoder combination
K1.1
K1.2
K2.1
K2.2
K3.1+K4.1+K5.1
K3.2+K4.2
K3.1+K4.1+K5.1
K3.2+K4.2
K3.1+K4.1+K5.1
Summary specification
Power Supply Voltage
Quiescent Current required (no relays activated)
Output current capability
Total output current capability (for whole Band Decoder)
Dimension
+12 to +15 volts dc
10 mA
350 mA per output
1000mA (limited by D1 or D3)
50x87mm
Any suggestion, comments or questions are welcomed at email ok2zi (at) atlas.cz.
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