The KD1JV designed Tri-Bander, sold by Pacific Antenna, is a three band QRP CW transceiver that may be configured in any three bands between 80 and 15 meters. For many reasons this is a very nice radio, but the kit configuration is best for home station use rather than portable use. This post outlines the modifications made to reduce receive current consumption, reduce weight and size, and change the controls and readout for better use in the field. While this does not turn the Tri-Bander into the ultimate SOTA rig, it gives good performance for a reasonable price.
The radio is a QRP CW superheterodyne transceiver that may be configured in any of three bands between 80 and 15 meters. The ability to operate on the 15 meter band, to take advantage of increasing sunspot activity, attracted me to the radio. I ordered a kit with 40, 20 and 15 meter band capability, making it a good match to a full size 40 meter end fed half wave (EFHW) antenna.
The aspects of the radio I liked include:
5 watts out at 13.8 volts on all bands
good 0.2 uV sensitivity
600 Hz audio filter
crystal IF filter
encoder tuned VFO
iambic B keyer
two message memories
Elements I did not like are:
relatively heavy and bulky metal case
receive current consumption of 90 mA
side facing knobs, band switch and display
toggle switch for band changing
position of menu pushbutton switch
LED display with poor sun readability
relatively large board size
I was able to address all but the last two elements that I did not like (LED display and board size). Using a PIC microcontroller and custom PCB, I changed the band switch to a push button with band indication, substituted latching relays to reduce receive current, relocated the menu push button switch, relocated paddle and antenna jack positions, and provided a top facing display and control knobs for field use. I also changed the DC power connector to be compatible with the power cables I use for my mtr3b and QCX mini. See figure 2 for the modified configuration.
After the modifications the current draw on receive is between 40 mA and 45 mA depending on the LED display value. The tribander has been used on two SOTA summits at the time of the writing of this post, W6/NS-306 Lowell Hill Ridge and W6/NS-306 KU6J Memorial Peak. The summits were successfully activated with QSOs on all three bands. The modified Tri-Bander was carried to the peak in a large ESD static shield bag, storing easily in my SOTA backpack. A full size 40 meter EFHW was used as the antenna on all three bands. The modified Tri-Bander was powered by a small 350 mAhr 3s LiPo battery. The only downside to the radio is that the LED display is difficult to read in daylight. A LCD display would be preferred but would take much effort to implement.
The design and assembly of the radio modifications are covered in the next sections. Schematics and Gerber Files for the custom PCB are available on GitHub. It will help to download the Tri-Bander manual with schematics for reference.
Much of the modification to the Tri-Bander involved band switching. The original configuration uses a toggle switch to change band operation. The switch does two things: turns on monostable relays to select input and output filters (figure 3a); and grounds a resistor divider to set the band for Tri-Bander's internal Atmel microcontroller (figure 3b).
In the modified Tri-Bander, a PIC16F688 microcontroller switches bands using a push button switch to rotate through the bands, replacing the toggle switch. The band push button switch fits on the printed circuit board better than a toggle switch would. The PIC microcontroller, replicating the original configuration, selects the appropriate relays for the input and output filters and band select resistors.
In the original configuration, relays 1 - 4 are conventional monostable relays that draw a continuous current when engaged. These relays consume about 30 mA current when selected. These relays are replaced with latching relays that only draw current when setting or resetting the relay contact position, eliminating 30 mA of receive current. To set or reset latching relays to the desired position a DC pulse must be applied to the set or reset coil. These pulses, nominally 3 milliseconds in duration, are generated by the PIC microcontroller.
Panasonic TX2SA-L2-5 surface mount dual coil latching relays are used in place of the monostable (non-latching) relays. This latching relay contact pinout matches the original relays but is offset by one pin. The non-energized contact position matches the latching relay reset position, and likewise for the set latching relay contact position and energized contact position. The coil voltages match as well. But the latching relay uses two coils, instead of one, with a different layout. The custom PCB comprehends this difference. The Panasonic relay is not always stocked so they can be difficult to procure. Other latching relays may be used but pinout configuration may vary. For example, the Kemet EE2-5TNU has the same contact arrangement in a dual coil configuration but the coil pinouts differ. So a modification of the PCB would have to be made. The priority is that the contact pinout is the same as the original relay. Figure 4 shows implementation of latching relays for the original relays 3 and 4. Signals R34s and R34r are the set and reset pulses from the PIC microcontroller. A positive going pulse will turn on the NPN transistor to latch the relay coil. Type 2N4401 transistors are used but any general purpose NPN switching transistor will work, assuming the it can handle the coil latching current pulse. A similar circuit is used for relays 1 and 2.
The PIC microcontroller also grounds the appropriate resistor for band selection and lights small, efficient LEDs to indicate band selection. The LEDs are a nice addition since the Tri-Bander LED display does not display the selected band. Figure 5 shows the implementation of selecting the appropriate band resistor. The signals 20m and 15m are from the PIC microcontroller, a high signal grounds the band select resistor and lights D1 or D2 for 20 or 15 meter operation respectively. When neither 15m or 20m is high, then 40 meter band operation is selected. Signal SW goes back to the internal Atmel microcontroller. Type 2N4401 transistors are used but any general purpose NPN switching transistor will work.
Controls and Connectors
The audio gain and frequency tuning controls, switches and jacks were all mounted on the metal case in the original configuration. My preference in portable operation is to have the controls and display facing up. To accomplish, this audio gain and frequency tuning controls were moved to the custom PCB. The signals to the frequency control encoder are from the original LED board socket, a header is used to connect to the audio signals for the audio gain control. The antenna connector and the paddle jack were all moved to the custom PCB as well. The DC power connector remains in its original place. A header is used at the headphone output to connect to a pigtail jack for the headphone plug.
Custom PCB Layout
The custom PCB is made to plug into the Tri-Bander main board. This is accomplished by using medium profile header sockets that stand .325" above the Tri-Bander main board. 3M type 929 series header sockets are used at the relay positions (8 sets of 5 pins), paddle 3 pin header position and the 16 pin LED board socket position. Using standard header pins assembled to the underside of the custom PCB, the custom PCB is simply plugged into the sockets. Most of the power, logic and RF signals are routed through these connections. Only the audio for the audio gain control has an external connection.
The location of the main board sockets determines the layout the custom PCB. Determining the socket locations with enough accuracy to ensure plug alignment is difficult with just one socket let alone the 10 locations required for the custom board. Fortunately the Tri-Bander main board was laid out such that the socket locations were all on standard 0.1" grid. The locations were determined by inserting male headers in each of the sockets on the main board and setting a large protoboard on the headers (figure 6). The locations of the sockets are determined by counting the spacing to a reference point. For the custom board, the LED socket pin closest to the board corner was the reference point (red circle in figure 6).
The locations of the display, audio gain and encoder, and push button switches were chosen next, followed by the antenna and paddle jacks. The layout of these components were modified slightly as other components were placed. The SOIC package for the microcontroller was chosen, all other components, except the latching relays, are through hole. A five pin header for programming the microcontroller is included as well.
The audio output was not brought to the custom PCB, there was no convenient way to do this. A header is used on the main board to connect to a headphone jack pigtail.
The main board and LED display board are assembled first following the Tri-Bander kit assembly instructions except for the following modifications.
Main Board Assembly
The main board, as supplied with the Tri-Bander kit, is assembled per the kit assembly instructions except for the following.
Place and solder 3M type 929 series header sockets at relay 1 - 4 terminals instead of installing the relays
Place and solder 3M type 929 series header socket at the 16 pin LED Display Board connector
Place and solder 3M type 929 series header socket at the 3 pin Paddle connector
Install and solder male 3 pin header at the audio gain (Vol) connector
Install and solder male 2 pin header at the Headphone (HP G) connector
Install a BNC connector on pigtails to the antenna connector terminals
LED Display Board Assembly
The LED board, supplied with the kit, is assembled per the assembly instructions except for the 16 pin connector and band B and C terminals. A straight 16 pin male header (SIP) is used rather than the right angle header called out in the instructions. Solder the 16 pin male header into the LED display board so it will plug into the corresponding socket on the main board. For best alignment, insert the male header into the 16 pin socket on the main board. Then place the LED board on the header and solder in place.
Also solder in a socket at the band B and C terminals so they can be grounded when switching to bands B or C. Note that this LED display board is only used to set up and align the Tri-Bander; the custom PCB will be used in the final configuration. The LED display board is shown in figure 8.
Figure 8 Top and Edge Views of the LED Display Board
Testing and Adjustment
After assembling the main and LED display boards, the Testing and Adjustment steps in the Tri-Bander Kit assembly instructions sections Power Up and Test, Receive Testing and BFO Adjustment, and Transmitter Testing need to be performed. To do this, temporarily use the LED display board plugged into the main board. You will also have to connect the volume control pot, V1 10 kOhm, to the Vol header, a paddle to the paddle socket, appropriate dummy load to antenna jack and headphone or meter to the headphone (HP) header. The terminals for the power switch should either have a switch connected or shorted together.
Band switching will be done manually by powering down the transceiver and shorting the appropriate relay socket pins and the band B or C sockets. Shorting with small loops of wire or shorting stubs on male headers may be used. Refer to the schematic in the assembly instructions for the appropriate relay and band select pins to short. Power the transceiver back up to perform the test and adjustment steps for that band. Figure 9 shows an example of a test setup.
After the transceiver has been tested and operation confirmed, then the custom PCB can be assembled and installed.
Custom PCB Assembly
The custom PCB is assembled in the standard method of low profile devices first followed by high profile devices. But there are a few critical steps to ensure proper operation of the board.
The PIC16F688 microcontroller is installed first along with the ICSP header (J2). The microcontroller is now programmed using a PICKit 3 or later programmer. The PICKit will need to supply Vcc to the microcontroller since there is no board power. If the microcontroller needs to be programmed after the rest of the board has been populated, then the board Vcc should be used.
The rest of the smaller components may be installed except for the resistors around the relay sockets J6 - J9 and J11 - J14. Do not install any of the remaining male headers (J1, J3 -J9, J11 - J14) or larger components such as the connectors, jacks, switches, encoder and potentiometer.
The next steps will align the custom PCB to the main board and install the latching relays in place. Insert the long ends of the male headers into the main board relay sockets, paddle socket and LED display board connector socket. The custom PCB is now put in place over the main board so both boards are aligned. After checking for proper alignment, solder the paddle and LED display board headers in place from the top of the custom board.
Now the surface mount latching relays will be placed on the board. The latching relays will be soldered in place on the male header pins that are protruding through the custom PCB from the main
board. In figure 10 the red pads are for the latching relay RY4 while the gold through hole pads are for the corresponding male headers J9 and J14. Pins 1 and 12 of the latching relay, the right most pins in figure 10, are not associated with a through hole. The latching relay does not have a lead at pins 2 and 11 so only a through hole is at those locations. As shown in figure 10, the pads for the latching relay leads are adjacent and slightly overlapping the through hole pads for the corresponding male header pins.
To solder the latching relays in place, first tack solder the pins of the male headers without a relay pad. Then place the latching relay so that its leads are aligned with the corresponding pads. Tack solder the latching relay in place, pins 1 and 12 of the latching relay are convenient for this. Then finish soldering the latching relay leads and male header pins. A fine point solder tip and a lighted magnifier come in handy for this step. Repeat at the other three relay positions.
Note that in figure 10, J14 pins 1 through 5 correspond to the main board relay pins 1 through 5 and J9 pins 1 through 5 correspond to the main board relay pins 6 through 10. The other relay locations follow the same layout scheme.
After the latching relays are in place, continue to assemble the custom PCB installing the rest of the components. A three pin female to female header cable will have to be assembled to connect the Vol header on the main board to the audio-in header (J4) on the custom PCB. Also an appropriate header to jack cable needs to be built for the headphone (HP) header on the main board. Refer back to figure 2 and the activation figures. To route +Vdd to the custom board, a jumper needs to be soldered from the polarity protect diode D3 cathode to pin 1 of either relay 1 or 3 - all on the main board. Also, the temporary BNC antenna jack should be removed from the main board.
The menu and encoder switches have the same operation as the original switches. Simply press the band switch to step through bands A, B and C. For my configuration bands A, B and C were 40, 20 and 15 meters. I silk screen labeled the custom PCB for these bands. Those labels may be changed for your particular configuration.
I chose not to build an enclosure for the transceiver. I did add a piece of acrylic to the bottom of the board using 3mm nylon spacers and screws. For many of my activations, this will be adequate protection of the board. Figure 11 shows the acrylic board and the Vdd jumper.
To operate, just hook a resonant antenna to the BNC connector, paddles to the paddle jack, and headphones to the the HP header. Then apply power and have some QRP fun!