Fullscreen HTML5Med Res (??MB)HTML4

By Andrew Woodfield, ZL2PD This Test Set is an integrated solution for simple go/no-go testing of HF QRP SSB transceivers. It measures 155 × 85 × 45mm and weighs under 220g, complete with its 9V rechargeable Li-ion battery. HF, SSB & QRP TRANSCEIVER TEST SET I ’ve been restoring and converting a series of decommissioned portable HF QRP SSB search-and-rescue (SAR) transceivers over the past few years. Converting these to amateur bands ensures that dozens of otherwise useful portable and handheld SSB transceivers don’t need to be discarded. QRP is radio parlance for ‘low power’, typically referring to transmitters up to 5W, while SSB stands for single sideband, a modulation scheme. Much of the design work for the initial conversions took place in my workshop. It’s equipped with the typical array of test equipment. When several of the MRS-1 yellow radios initially arrived on my bench after the closure of the MRS service in 2024, they were accompanied by several very large grey plastic boxes, each about the size of a couple of loaves of bread. A few faded panel labels indicated these were used to test the two-­channel MRS-1 and MRS-3 radios. I used one of these test boxes briefly to verify the status of several transceivers prior to their conversion for use on the 80m and 40m amateur bands. A BNC connector on each box provided a connection for a cable to the transceiver antenna connector. Eight AA alkaline batteries were fitted internally to power the test set via a three-minute timer. A large meter mounted on the front panel displayed the transceiver RF output power. An internal crystal oscillator generated the two fixed 3MHz MRS HF frequencies. These were used to monitor the modulation during transmitter testing and provided accurate signal levels of about -90dBm and -105dBm for receiver testing. Other test box functions permitted a twotone ‘selcall’ system to be tested with the help of other external test assemblies and cables. A quick look inside these boxes revealed a rat’s nest of wiring, a multitude of prototype boards and circuit mysteries worthy of Agatha Christie. There was no documentation. So modifying these for other purposes was out of the question, but the idea of a simple tester stuck with me. Designing a new Transceiver Test Set (TTS) Faced with many radios to be tested during the upcoming club’s conversion workshops, a similar integrated Fig.1: the Transceiver Test Set (TTS) provides a basic test system for HF QRP SSB transmitters, receivers and transceivers. 74 Silicon Chip Australia's electronics magazine test system designed to cover a wider range of HF frequencies would be very useful. So, with the functions of the original test boxes in mind, I set out to create an updated design that would be capable of testing any HF QRP SSB transceiver. The features I considered most useful included: • Frequency range: 400kHz to 40MHz • Tuning steps: from 10Hz up to 1MHz • RF power meter: 5-10W full-scale • 50W dummy load: capable of handling 5W continuously or 10W for brief periods • Transmit modulation monitor: via an internal speaker • Receiver sensitivity test: with internal RF signal generator (-85dBm and -100dBm levels) • Transceiver frequency checking: using receiver and/or transmitter tests • Dual-mode operation: USB and LSB (to cover all HF bands) • Power supply: a 9V PP9 battery or a similar capacity rechargeable battery • Internal calibration: allows precise alignment of the PLL oscillator frequency Fig.1 shows the block diagram of the resulting Transceiver Test Set. The TTS comprises a wideband direct conversion receiver (DCR) with a digital PLL VFO, an attenuator/dummy load and an RF power detector. The attenuator/load and RF power detector form an RF power meter, and the DCR is used to monitor transmitter modulation. In addition, the VFO signal can be used as a simple RF signal generator to test the SSB receiver. The VFO can be tuned from 400kHz to 40MHz. The siliconchip.com.au required SSB mode may be selected, either USB or LSB. This selection will result in a 1kHz audio tone being audible in a USB or LSB receiver correctly tuned to that frequency. The test mode, TTS operating frequency and measured results are shown on a two-line alphanumeric LCD screen. The nominal carrier frequency is displayed, accurate to ±20Hz. The three test modes can be selected using the Mode selection pushbutton. Test mode one is used to test transmitters, while the second and third modes are used for testing receivers. The latter two modes deliver a -85dBm and -100dBm signal to the receiver, respectively. The operating frequency is displayed on the LCD screen. This may be tuned in steps of 1MHz, 100kHz, 10kHz, 1kHz, 100Hz or 10Hz. The selected test mode is shown in the upper-left corner of the LCD screen: TX for test mode one, RX H for mode two, and RX L for mode three. When testing transmitters, the RF power is displayed using a bargraph on the lower line of the LCD. The meter FSD can be adjusted internally and set to a convenient level, typically from 5W to 10W. Circuit details Fig.2 shows the circuit diagram of the main RF section of the TTS. The HF SSB QRP transceiver (or transmitter or receiver) being tested is connected to the RF Input connector, CON1(a), in Fig.2. When testing a transmitter, the RF detector stage (D1 and the 10nF capacitor) rectifies the transmitter RF signal. Typically, for a QRP transmitter or transceiver, this may range from 1W (+30dBm) to 5W (+37dBm). This DC signal is passed to the microcontroller via trimpot VR2, a resistor network and pin 5 of CON2 (more on where it goes later). This voltage is measured and displayed as a bar-graph RF power display on the lower line of the LCD screen. The signal at pin 5 of CON2 must not exceed 3.3V DC, as that is the most that the microcontroller used to measure it can handle. The transmitter signal is both terminated and attenuated by the 50W 60dB attenuator shown in the dashed cyan box in Fig.2. The RF power detection circuit described in the previous paragraph is connected in parallel with this 50W attenuator/load. The first section of the attenuator uses three 2W-rated resistors, selected to handle typical QRP transmitter output power, as part of three series-­ connected T-type attenuators. The frequency response of the resulting 60dB fixed RF attenuator (and transmitter load) is flat (within ±2dB) from below 1MHz to about 150MHz, despite its simple construction. When testing a typical 5W (+37dBm) QRP transmitter, the signal at the output of the attenuator is about -23dBm. This passes through a wideband RF buffer (Q1). This stage introduces a signal loss of 3-4dB. More importantly, it also features 30dB of isolation in the reverse RF path direction, ie, from the buffer stage’s output to input. These losses are near-flat for frequencies from below 1MHz to above 50MHz. The buffer output signal generated by the transmitter is then mixed using a Polyakov dual-diode mixer. The diodes in the Polyakov mixer switch twice per VFO cycle, during the positive and negative peaks of the oscillator sinewave, as the oscillator voltage exceeds the forward voltage of each diode. This requires the VFO to be set at half of the transmitter frequency for correct demodulation. This approach avoids the potential problems with direct low transmitter energy coupled from the transmitter and mixing directly in the VFO when used with conventional diode mixers. The mixer is driven by a square wave output from the Si5351A PLL chip. This waveform is ideal for both conventional diode double-balanced mixers and the Polyakov diode mixer. For more details on this, see H.P. Walker, “Sources of intermodulation in diode-ring mixers”, Radio and Electronic Engineer, Volume 46, Issue 5, May 1967, pp247-255. Since all the preceding wideband stages are untuned, the VFO signal Fig.2: the TTS attenuator/load, RF power detector, RF buffer, Polyakov mixer and audio stages are in this section of the circuit. siliconchip.com.au Australia's electronics magazine August 2026  75 The prototype for the Transistor Test Set was relatively easy to build, with pretty much all wiring made using DuPont-style connectors onto regular pin headers for ease of construction. used in a Polyakov mixer can also be readily radiated via the mixer input. If the buffer stage were not present, this VFO signal could measure as much as -55dBm to -65dBm at the RF input connector. However, the 30dB reverse isolation of the RF buffer, combined with the 60dB loss of the attenuator, ensures that this low mixer port isolation causes no problems during transmitter testing. The unwanted emissions at the test set input are less than -85dBm, more than 120dB below the level of the typical 5W QRP transmitter’s RF output. The Polyakov mixer demodulates the SSB transmitter audio when the VFO and transmitter are correctly tuned. This audio is amplified by NPN transistor Q2, filtered by L1 and its three connected capacitors, and further amplified by IC1 to drive the TTS monitor speaker. Digital oscillator & LCD screen Fig.3 shows the other half of the circuit, on a separate board. The two circuits are joined via CON2 in Fig.2. GND and VBAT on CON2 connect to CON7 in Fig.3; the RF signal from CON2 goes to pin 1 of IC2; and the VFO IN signal on CON2 comes from the OUT0 connector (CON8) in Fig.3. An 8-pin ATtiny85 microcontroller (IC2 in Fig.3) controls the TTS operation, including driving the LCD screen and the 10-pin Si5351A PLL chip (IC3). Rotary encoder RE1 is monitored by the ATtiny85 via its PB3 digital input. The three connected resistors provide a 2-bit DAC function, allowing direction of rotation and switch presses to be detected using a single pin. The pin’s voltage is monitored using the ATtiny85’s internal analog-to-digital converter (ADC) to allow it to distinguish the different actions. The I2C LCD is controlled by an on-glass ST7032 chip, which supports the standard alphanumeric LCD commands via I2C rather than the more typical parallel connections. This display is not equivalent to the standard alphanumeric LCD with the ‘added backpack’ I2C-to-parallel sub-board. This LCD is a more compact and better-­ integrated display. We suggest using the JLX1602 2-line, 16-character alphanumeric LCD for this project. To find one, search for “JLX1602” or “ST7032 I2C LCD”. One source is given in the parts list. The Midas MCCOG21605 range of I2C LCDs are also available in the UK. These are more expensive and differ in size and pinout. The PCB and software are designed to accept these LCD screens without any changes to the hardware or software. Only one of the Si5351A’s three outputs is used in this design (OUT0), although a second output (OUT2) is used briefly during calibration. The VFO output frequency at OUT0 depends on the operating mode of the TTS. When testing a transmitter in test mode one, the +7dBm VFO signal Fig.3: the TTS VFO uses an 8-pin ATtiny85 microcontroller to control the Si5351A PLL chip and the I2C LCD. It also monitors the user inputs from the rotary encoder and switches. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au simply drives the Polyakov mixer’s oscillator input at half the transmitter frequency. “TX” is displayed in the top right-hand corner of the LCD during this mode. For testing receivers, in test mode two, the TTS generates an RF input signal for the receiver of about -85dBm (about an “S5” or “S6” moderately strong signal on a typical receiver S-meter), while test mode three gives a lower signal level of about -100dBm (about “S2” or “S3”). The VFO in mode two operates at a frequency 1kHz offset from the receiver frequency, 1kHz above or below the nominal carrier frequency depending on the USB and LSB selection switch state. “RX H” is shown on the LCD during this test. In mode three, the VFO operates at half the nominal carrier frequency, plus or minus the required offset. “RX L” is then displayed on the LCD. This uses an oscillator harmonic with a reduced output level for this test. The 1kHz offset in each case generates an audible 1kHz tone in the SSB receiver being tested when it is on the correct frequency. In these receiver test modes, the VFO oscillator signal passes through the mixer to the mixer input with a loss of around 6dB, then on through the RF buffer with a reverse isolation loss of 30dB. The signal then flows back through the attenuator, adding another 60dB loss, and finally into the receiver. Both modes two and three produce a 1kHz audio tone in a correctly tuned on-frequency receiver. However, if desired, the VFO frequency can be manually tuned to give other demodulated tones between, say, from 300Hz to 2400Hz, to check the SSB receiver audio response. A low-cost 3.3V regulator (REG3) supplies the majority of the digital sections of the TTS, while the 9V battery voltage coming from the RF board directly supplies the RF and audio sections. Construction The TTS is built using two PCBs, one for the VFO and LCD (coded 06104262, 89 × 36mm), the second for the RF and audio sections (06104261, 75 × 48mm). Their component overlay diagrams are shown in Figs.4 & 5. The parts for the individual boards are listed separately in the parts list, but siliconchip.com.au Converting fixed channel SSB transceivers The first radio converted was the handheld Codan/Condor 8332 1W SSB transceiver (Photo a). A very compact phasing SSB radio, the changes included migrating from USB operation on two crystal-­ controlled 3MHz & 5MHz channels to variable frequency oscillator (VFO) operation on the 80m and 40m amateur bands, and lower sideband (LSB) using a digital PLL VFO (see www.zl2pd.com/Condor_SAR_ Transceiver.html). The conversion was made possible with a version of my low-cost compact SugarCube PLL VFO module (www.zl2pd.com/ sugarcube_plus.html). This module uses an 8-pin ATtiny85 microcontroller, a Silicon Labs Si5351A PLL chip and an OLED display on a compact 25 × 25mm PCB. It delivers up to three synthesised PLL oscillator outputs from 5kHz to about 290MHz. Following the successful Codan/Condor transceiver conversion, the much larger AWA TR-105 transceiver (Photo c) was next in line (www.zl2pd.com/TR105.html). And once that was completed, I moved on to the newest conversion, the recently withdrawn Mountain Radio Service (‘MRS’) MRS-1 portable HF SSB transceivers (www.zl2pd. com/MRS-1_Conversion.html). With a growing number of these transceivers now successfully converted by local club members, I’m considering its successor, the very compact MRS-3/SR-3 transceiver (Photo b). All these transceivers, each finished in a distinctive bright yellow colour, are battery-­powered HF SSB QRP transceivers with RF outputs ranging of 1W (Condor), 3-4W (MRS-1) or 5W (TR-105 and MRS-3). These receivers also feature good sensitivity. The MRS-1 (Photo d) and TR-105 are particularly robust, the former featuring a yellow painted aluminium shell and integrated battery holder, the latter having a very heavy duty ABS plastic case and clip-on battery pack. The MRS-3 handheld has a very sturdy clamshell-style diecast aluminium case. off-board components that are wired to that board are part of the general parts list. The various connectors, switches and other user controls are wired to these boards. The PCB layout diagrams show the location of the components. The prototype RF/audio PCB was built using a single-sided PCB (see the photo on page 76), which was Australia's electronics magazine Photos a & b: the Codan/Condor portable QRP HF SSB transceiver (left), and the MRS-3/SR-3 portable QRP HF SSB transceiver with two-tone call option (right). Photo c: the TR-105 portable QRP HF SSB transceiver. Photo d: the converted MRS-1 transceiver. perfectly satisfactory. Provision was also made for the addition of shields around sections of the attenuator, but that was found to be unnecessary. There are three 2W resistors on the RF/Audio PCB. Space these about 1-2mm above the PCB when mounting them. If you can’t find 2W resistors (local retailers stock 1W and 5W types but nothing in between), you could use pairs of 240W 1W resistors soldered in August 2026  77 Fig.4: follow this diagram while installing the components on the RF board. The only slightly tricky part is T1, which has three windings. Compare the 1-6 numbering of its pads to what’s shown in Fig.2. Fig.5: start assembly of the control board by soldering IC3 as it is delicate. Make sure it’s orientated as shown, with its pin 1 marker at lower left. Apply flux paste to the pins before soldering, and if you accidentally bridge them, use more flux and some solder wick to clear them. parallel for each, with a few millimetres between the bodies. Components of particular note include the 100mH choke used for the audio low-pass filter, the FT3761 toroid (T1 in Figs.2 & 4) used in the Polyakov mixer, and the I2C LCD (LCD1), which mounts on the back via one of three possible header locations. None of these are terribly hard to find or expensive; all three can be found from the usual internet suppliers (see the parts list). A toroidal core from an old fluorescent lamp inverter can also be used for T1. T1 is made using three 200mm lengths of thin enamelled copper wire, say 34SWG or 0.2mm diameter. Hold these three wires together and wind 10 turns onto the toroid. Twisting the three wires together a little to hold them together is helpful but not essential. This arrangement forms a ‘trifilar’ winding. Connect the various wires from T1 as shown in Figs.2 & 4 (the points numbered 1-6 in Fig.2 correspond to the similarly numbered points in Fig.4). I mounted T1 flat on the PCB in the prototype, but some may find it easier to mount it vertically. Either approach is satisfactory. The VFO PCB provides for two sizes of Midas I2C LCDs and the lower-cost JLX1602 I2C LCD. It also allows the Si5351A chip to be mounted on a separate MSOP-10 to DIL-10 adaptor board if necessary. Two of these through-holes (pins 7 & 8) are used to allow the 3.3V rail and ground to be carried to the RF/Audio PCB. This can be seen in the wiring diagram, Fig.6. If you purchased a programmed ATtiny85 chip, it can be carefully plugged into the socket on the control board now, with its pin 1 end lined up with the socket notch. If you have a blank chip, you will need to program it first (see the panel opposite). When all the components have been mounted on the VFO PCB, the LCD may then be mounted on the back. The LCD’s backlight and connection pins require careful handling. If using the recommend (JLX) LCD, the two backlight pins go into the pair of holes visible on the right-hand side of Fig.5. The other LCDs use a pair of slots near REG3 (a different pair depending on the LCD size). In either case, the LCD screen should only be fitted after all other parts have been mounted on the board. I made a simple laser-cut box from 1.6mm birch ply with cutouts for the LCD screen, controls and speaker. All sides except the lid the speaker is attached to are glued together. I used a fast-setting PVA glue. I glued four 15mm-long M3 threaded nylon standoffs in each corner, about 4mm below the upper edge of the box, so the top cover could be attached using 12mm-long M3 panhead screws. The files for the laser-cut box can be downloaded along with the software and 3D-printing files from siliconchip. au/Shop/6/3583 I printed the front panel artwork on a sheet of plain paper, carefully trimmed using a sharp scalpel and covered it with self-adhesive transparent film from a stationery supplier. The reverse side was sprayed with artwork spray adhesive and then applied to the birch ply front panel. This process makes a very tidy, inexpensive and hard-wearing panel, but it is a little time-consuming. The Transceiver Test Set measures just 155 × 85 × 45mm and weighs under 220g. It’s powered by an internal 9V rechargeable Li-ion battery. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au With the panel made, the VFO board and display can be mounted on the front panel using four M3 × 15mm panhead machine screws and bolts. Fig.6 shows how the internal wiring is arranged. Three resistors are mounted at the rear of the rotary encoder. If after assembly your rotary encoder tunes the VFO in the opposite direction, swap the 1.8kW & 3.9kW resistors that are soldered directly to it. The 9V battery used in the prototype is a rechargeable LiPo type with an integrated charger. The manufacturer’s claimed 6600mAh capacity is, unsurprisingly, exaggerated. It is actually closer to 1300mAh, but that is still adequate for many hours of testing. Recharging via a phone charger or other USB-C power source is relatively fast and convenient. I made the VFO tuning knob and volume knob on my 3D printer, but commercial equivalents are readily available. If you wish to print these yourself, the relevant STL files can be found in the download above. The monitor audio level is infrequently adjusted, so that control has been relegated to the rear panel, along with the RF connector and power switch. Programming the ATtiny85 Download the HEX and EEP files for the Transceiver Test Set from siliconchip.au/ Shop/6/3583 If you have an in-circuit programmer like the USBasp, you will also need a way to connect the correct lines to the pins on the chip. This is most easily done using an adaptor board. It saves adding a 6-pin programming socket to each PCB. My 8-pin adaptor was published in the September 2020 (on page 47; siliconchip.au/ Article/14563) and the PCB is still available (siliconchip.au/Shop/8/5642). Once you have the chip plugged into an adaptor, connect the programmer to your computer. Download and open a programming application (such as Extreme Burner) and load the HEX and EEP files into this program. Now program your ATtiny85 with the HEX file, then the EEP file. Click on the “Write” tab in Extreme and select the file you are sending to the ATtiny85. Next, program the hardware configuration fuses in the ATtiny85. Table 1 shows the required fuse settings. You need to set these after loading the HEX and EEP files before the TTS will work. These configure the ATtiny85 for operation from the 8MHz RC clock and the internal reset mode to free up pin 1 for RF power measurement. To set the fuses, click on the Fuse Bits/Setting tab, enter the values shown, and click on the Write selection boxes for the Low and High fuses (the others may safely be ignored). When you have done this, write the fuse settings to the ATtiny85 by clicking on the Write button at the lower right of this tab. If necessary, detailed step-by-step programming instructions can be found on my website, www.zl2pd.com Fuse Hexadecimal value Comment Lock byte FF Flash not locked Extended byte FF Self-programming disabled High Byte 5F Defaults except RSTDISBL=0 Low byte E2 Defaults except CKDIV8=0 Table 1 – the required ATtiny85 fuse settings TTS Frequency Calibration The Si5351a VFO must be calibrated to ensure the TTS is accurately tuned to the nominal carrier frequency shown on the display. This is determined by the precise frequency of the 25MHz reference crystal attached to the Si5351A. The ATtiny85 program calculates the settings of the Si5351A using this value to set the correct VFO output frequency. Fig.6: the front panel (lower ▶ PCB) has been artificially folded flat in this sketch to show the internal wiring. siliconchip.com.au Australia's electronics magazine August 2026  79 Since these crystals are inexpensive, their frequency may vary by more than 3kHz from 25MHz. Any error in the value of this crystal’s frequency that is permanently stored in the VFO microcontroller’s EEPROM will directly impact the accuracy of the VFO output. To ensure this value is accurate, the software contains a VFO calibration routine. To calibrate the TTS, switch off the power, then switch it on again while holding down the Mode pushbutton. After the initial power-up screen has been displayed, “Calibration” will be seen on the LCD. Now release the Mode pushbutton. The VFO will now be delivering what it calculates to be a 25.000000MHz square wave of about 3V peak-to-peak via the Si5351A’s OUT2 output, which can be found at CON10 (“Cal”) on the VFO board. Connect an accurate frequency counter to the output on CON10. This should display a value within 3-4kHz of 25MHz. Tune the TTS VFO tuning knob until the frequency counter displays exactly 25.000000MHz. You can use the tuning step pushbutton shaft switch on the tuning control to select the desired tuning step size. When the frequency counter is displaying a frequency as close as possible to 25.000000MHz, press and hold the Mode pushbutton for about half a second. Now switch off the power to the VFO and reconnect the frequency The TTS rear panel can be seen here with the transmit audio monitor volume control, power switch and RF connector while testing an MRS-3 transceiver. counter to the VFO PCB’s OUT0 connector (CON8). Switch on the power again. Confirm that the frequency counter shows the correct frequency. Be careful to note that each test mode results in an output frequency that differs from the displayed frequency: Test Mode 1: TX Test VFO CLK0 = Displayed frequency ÷2 Test Mode 2: RX High Level Test VFO CLK0 = Displayed frequency ±1kHz Test Mode 3: RX Low Level Test VFO CLK0 = (Displayed frequency ±1kHz) ÷ 2 The 1kHz offset will depend on the setting of the USB/LSB switch, ie, LSB = -1kHz, USB = +1kHz. If the output at OUT0 (CON8) agrees with the frequency counter display, the TTS VFO is calibrated. Final adjustment & operation Songbird An easy-to-build project SC6633 ($30 plus postage): Songbird Kit Connect a fresh 9V battery and switch on the power. The initial poweron message should appear. This is shortly replaced by the transmitter test (Mode 1) display with frequency and that is perfect as a gift. Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 current tuning step size. Turning the Tune/Step knob will change the frequency, and pressing in the encoder knob will change the tuning step size. Pressing the Mode pushbutton should change the displayed mode. Changing the LSB/USB selection switch will not change the display on the LCD, but it does alter the output frequency in (receiver) test modes two and three. Use the Mode pushbutton to set the test mode to (transmitter) test mode 1. Adjust the TTS for the nominal carrier frequency of the transmitter being tested, then set the USB/LSB switch for the required mode. Set VR2 to approximately midrange, connect a QRP SSB transmitter and adjust VR2 to set the required LCD RF power meter maximum level. The meter is reasonably linear from 0.2W to 5W when set for a full-scale of 5W, for example. Modulate the transmitter with voice or an audio tone. The monitor volume can be adjusted to give a suitable level for monitoring the transmitted audio. Avoid transmitting into the TTS for long periods to avoid overheating the internal attenuator/load. It is designed for testing 5-10W SSB transceivers. Select (receiver) test mode two and the required USB or LSB setting, then confirm that a 1kHz tone is clearly audible in the receiver being tested. This test assumes the receiver has a sensitivity of, say, 1μV for a 10dB signal-­to-noise ratio (SNR) or better, and the displayed TTS frequency matches the nominal carrier frequency of the receiver. Now select test mode three. This reduces the signal into the receiver by about 15dB. On a sensitive receiver, the 1kHz tone should be audible above the noise floor with the standard 3kHz SSB speech filter receiver passband. Parts List – Transceiver Test Set 1 laser-cut or moulded instrument case, 154W × 44H × 84D (mm) or larger 1 9V PP9 battery and snap [for snap: Jaycar PH9232, Altronics P0455] 3 2-pin headers, 2.54mm pitch (CON1, CON3, CON5) 1 BNC female panel-mounting socket (CON1a) [Jaycar PS0658, Altronics P0516A] 1 5-pin header, 2.54mm pitch (CON2) 1 3-pin header, 2.54mm pitch (CON4) 1 panel-mount pulse-type rotary encoder with integrated push switch (RE1) [AliExpress 1005005983134515] 2 SPDT panel-mount toggle switches (S1, S3) [Jaycar ST0336, Altronics S1315] 1 panel-mount pushbutton (S4) [Jaycar SP0711] 1 57mm 8W loudspeaker (SPK1) [Jaycar AS3000, Altronics C0610] 1 10kW log panel mount potentiometer (VR1) [Jaycar RP3610, Altronics R2214] 2 knobs, to suit RE1 & VR1 4 M3 × 20mm tapped nylon spacers 8 M3 × 10mm panhead machine screws 4 M3 × 20mm panhead machine screws and hex nuts 4 M3 × 6mm panhead machine screws and hex nuts a selection of wires terminated with DuPont female connectors (cut jumper wires in half) various lengths and colours of light/medium-duty hookup wire RF/Audio board parts 1 single-sided PCB coded 06104261, 75 × 48mm 1 47μH axial RF choke (RFC1) 1 100mH radial RF choke (L1) [AliExpress 4001355154716] 1 FT37-43 toroidal core (T1) [Minikits FT37-43 or AliExpress 1005009245292057] 1 600mm length of 0.15-0.2mm diameter enamelled copper wire (T1) 1 100kW top-adjust trimpot (VR2) 1 8-pin DIL IC socket (for IC1) Semiconductors 1 LM386 audio amplifier IC, DIP-8 (IC1) 1 J310 N-channel VHF/UHF JFET or equivalent (Q1) 1 BC548 30V 100mA NPN transistor (Q2) 3 1N4148 75V 200mA signal diodes (D1-D3) Capacitors (all 50V radial ceramic unless noted) 1 100μF 16V radial electrolytic 2 15nF polyester or MKT 3 10μF 50V radial electrolytic 2 10nF 5 100nF 1 4.7nF polyester or MKT 1 47nF polyester or MKT Resistors (all ¼W ±1% axial unless noted) 1 220kW 1 10kW 3 120W 2W 2 82W 4 10W ½W 1 18kW 1 1kW 2 100W 1 39W 1 0W VFO/Control board This Transceiver Test Set is a simple, easy to build and lightweight portable test system. It has proven to be ideal for the task, and a very worthwhile successor to the original crystal-locked test box. The TTS has been invaluable in testing a wide variety of QRP SSB transceivers in my workshop, and in the series of conversion workshops undertaken locally at our radio club. I’m certain you’ll find it equally useful for testing your QRP transceivSC ers, too. 1 double-sided PCB coded 06104262, 89 × 36mm 5 2-pin headers, 2.54mm pitch (CON6-8, CON10-11) 1 4-pin header, 2.54mm pitch (for connecting RE1) 1 JLX1602 I2C 16×2 alphanumeric LCD (LCD1) [AliExpress 32807890814] OR 1 Midas MCCOG21605-series 16×2 alphanumeric LCD (LCD1) [element14/RS] 1 25MHz HC-49 crystal (X1) [AliExpress 1005002830871853] 1 8-pin DIL IC socket (for IC2) Semiconductors 1 ATtiny85-20PU 8-bit microcontroller programmed with 0610426A.HEX, DIP-8 (IC2) 1 Si5351A-B-GTR 3-output PLL clock generator IC, MSOP-10 (IC3) [AliExpress 1005008517358757] 1 TS2950CT33, 78L33 or equivalent 3.3V 100mA regulator, TO-92 (REG3) [AliExpress 1005006134947908] Capacitors (all 50V radial ceramic unless noted) 1 10μF 50V radial electrolytic 3 1μF 50V radial electrolytic 4 100nF Resistors (all ¼W ±1% axial) 3 10kW 1 3.9kW 1 2.7kW 1 1.8kW 1 470W 1 0W siliconchip.com.au Australia's electronics magazine Conclusion August 2026  81