I have always been spurred on in my radio activities by the desire to get onto higher and higher frequencies so when I saw that kits for puting together a 122 GHz transceiver were becoming available I could not resist getting one. I ordered the 122 GHz populated PCB designed by Andrew Anderson VK3CV / WQ1S and produced by Tim Tuck VK2XAX. It duly arrived about six weeks ago. I decided to make the antennas myself as I have a small lathe and enjoy a bit of machining now and again. I produced two antennas as per the original drawings supplied as part of the project. The board is pictured below.
I boxed up the board and mounted my circular horn on the PCB and arranged for the horn to protrude through the box.as shown below.
Locally to me Peter bates GM4BYF had also bought a set of bits to build up a system so there was the possibility of having some QSOs! Earlier this week I visited Peter and we had a preliminary test acoss his garden and then went out to do a test over a longer path. Fortunately my home town of Edinburgh is endowed with plenty of hills. Peter went onto the Blackford hill and I set up shop on the Braid hill and we had a QSO over a path of 0.68 km.
We believe this is the first GM to GM contact on the 122 GHz band. Once we got the horns lined up the signals were S5 to S7 and good copy on FM. There was some QSB on the signals which we attributed to a tree which was close into the path and it was quite windy. This test showed up a few deficiencies in my setup.and a couple of days later I improved the mounting and antenna pointing arrangement for my transceiver. It also was apparent that I was overdeviating and I corrected that.
Flushed with success from our first QSO we decided that we would try to have a cross border QSO GM to G! We considered a number of locations around Coldstream on the A697 and Carter Bar on the A68. Finally Peter spotted a disused rail way line that crossed the border just east of the town of Kelso. As the Carter Bar site was likely to be busy with people visiting the border viewpoint the disused railway sounded better proposition!
I have owned a FT736R for about 25 years and have always been happy with it. It has given me good service. It is fitted with the 6m and 23 cm modules. A widely recognised weakness with the radio is its switched mode power supply. It is an elderly design that is quite inefficient by present day standards and runs hot on account of four high wattage resistors which dissipate energy. One consequence of this is that several of the electrolytic capacitors “dry out” over time and lose their capacitance to a point that the power supply will not start up when switched on. Most other owners I know have re-capped their power supplies and I was no exception. Additionally, about a year ago my unit developed another fault whereby by the supply would make a ticking noise on transmission speech peaks. This was eventually traced down to a 10 mH inductor in the feedback circuitry which had gone open circuit. A replacement was sourced which seemed to cure the fault but I noticed that on transient loads and speech peaks the power supply kept tripping. I assume that it was probably due to the replacement inductor not having exactly the same characteristics as the original Yaesu part which looked to be a “special”. I decided it was time to think of replacing the whole PSU.
I remembered that I had seen an article some years ago about fitting a replacement by Harvey Laidman, W8DX in CQ Magazine but could no longer find a copy. I believe it was in the june 2006 issue on page 28. I found mention of the article on the FT736R IO Group and found that this was the part recommended . It seemed to be available in the US but was on a long lead time so I started to search about for a more available part. As I wanted to use the original enclosure to encase/screen the replacement it had to fit in a footprint of 80 by 140 mm and be less than 40 mm high. I also wanted the replacement to have a good EMI specification. Most of the standard modular supplies have a width of 90 mm and would not fit the available space. I looked at the catalogues of the usual distributors and settled on a unit manufactured by XP Power, the ECM100US12. This has a footprint of 64 by 115 mm and height of 31 mm so would fit comfortably inside the original casing. It also runs from either 110 V or 230 V line voltage without switching. It is available for around £70 - £80 from a number of different UK/European component suppliers such as RS, Farnell and CPC and sometimes appears on EBay. The data sheet states it has industrial and medical approvals and it uses a two section mains input filter with two cascaded bifilar (common mode) chokes. It can supply up to 8 amps which is more that the radio requires on FM modes. Although it is nominally a 12v supply it can be adjusted up to 13.4 V which runs the radio quite adequately.
To fit a replacement first remove the original PSU from the radio. To do rhis remove the three screws on the heatsink back plate, and the two self tappers securing the PSU base at the front of the unit. Slide the PSU forward and raise it from the main chassis. The cable clamp/bush in the back panel can now be released to take the PSU free of the chassis complete with the 6-way JST connector. The PSU can now be dismantled by removing the screws securing the perforated cover and the PCB to the base plate. Recover all of the metalwork including the heavy gauge aluminium end plate. Carefully store all the screws as these will be required for re-assembly. Cut a piece of 18 SWG sheet aluminium to the same size as the PCB to act as a mounting plate for the new PSU and drill six fixing holes using the PCB as a template. (Two are for the aluminium end plate.) Also drill fixing holes for the new PSU and mount it on short pillars. Short leads with line input (3-way Molex) and DC output (12-way Molex) connectors were prepared. (Connector details are below).
The power supply with connectors and short tails. The Molex connector shells and pins were as follows from RS. Links are to the RS catalogue. (A slight cock-up was made in ordering to 12-way output connector but a 6-way one sufficed!). Pins 9 -12 are unused.
SPOX 3.96mm female crimp housing, 3 way
SPOX 3.96mm female crimp housing, 12 way
Crimp Term,18-24AWG,phosphor Bronze,reel
The short tails were connected to the original Yaesu cabling with crimp connectors.
The PSU assembled into its original casing and back in the radio. The aluminium baseplate is visible where the PCB with the input and output connections and the voltage selector were.
While I was working on the radio and had it apart I decided to rewire the internal mains switch to improve safety. The Power switch on the front panel it is a 2-pole mains voltage rated part but one side is used to switch the 13.8 V DC line while the other side is used as the 230V mains switch. The problem is that the switch is in the neutral side of the power feed to the PSU. This is very bad practice as the live is permanently connected to the PSU. The Y-Capacitors in the PSU are subject to full mains voltage as long as the radio is connected to the mains. NOT GOOD!!! I decided that as I had only ever run it off a DC supply to test it I could dispense with the low voltage switching and use the double pole switch to properly isolate the radio from the mains when switched off.
I was able to do it by running new correctly colour coded line and neutral wires to the front panel switch and I was able to utilise the existing Yaesu (white) wires that were already in the harness as the returns to the fuse and backplate. I also had to rearrange the fuse wiring. I now have it arranged so the L and N come off the pcb on the back of the IEC socket directly to the switch. The fuse has been rewired so that it is in the L return from the switch before going to the 6-pin JST connector on the back. The L and N pins on the JST socket have been swapped as I was trying to preserve the original wiring as much as possible, but I see no harm in that. I have cut a piece of clear plastic so that it clips over the back of the mains socket to prevent the ingress of passing fingers as had happened! I also enclosed the front panel mains switch in heat shrink.
Overall the radio runs much cooler with its new more efficient power supply and will hopefully continue to give good service for some years.
31 May 2020.
The ADF 5355 is a versatile fractional N synthesiser that covers the frequency range 54 MHz to 13.6 Ghz . It uses and on-chip VCO arrangement and is capable of milliHertz frequency resolution at 10 GHz. They are readily available from Chinese vendors on the usual auction sites incorporated into basic development boards. The cost of these boards is comparable with the cost of the chips in one off quantities. For some time I thought that a useful signal generator could be produced based on one of these boards.
In the past I have used them for low powered personal beacons and as local oscillators and signal sources all programmed with Arduinos. Recently I came across the Arduino based signal generator design by Christian Petersen DD7LP based on the ADF4351  and I used his Arduino “sketch” as the starting point for my project. The ADF5355 is capable of operating with frequency steps of milliHertz at 13 GHz, and to have the required arithmetic precision for one Hertz resolution was going to be beyond the capabilities of an 8-bit Arduino ATmega328P. It also has a more complex register structure than the ADF4351. Fortunately there are a number of much more powerful processors supported in the Arduino IDE which are well provideded with libraries and example code.
The ADF5355 gets its very high frequency resolution by two fractional parts to programme its frequency. To have resolutions of the order of Hertz the micro controller must be capable of calculations with around 12 decimal digits which implies a 32 bit controller using double precision arithmetic is required. Details of the register programming are in the datasheet .
One suitable 32 bit Microcontroller is the WeMOS SAMD21 ARM Cortex M0 which runs at a 48 MHz clock rate. It is supported in the Arduino IDE and if programmed appropriately is capable of the necessary arithmetic precision. It is also available mounted on a pcb with a USB programming interface in the well established Arduino hardware format, Ref . Other options would be some of the Maple Leaf boards using ST Microelectronics STM32 chips.
For this project I choose a SSD1306 1.3 inch OLED display. These are available in either I2C or SPI versions. The 0.96 inch variant is more common but requires good eyesight! I sourced the 1.3 inch mounting PCB and the 1.3 inch display separately and assembled my own. Although the display is small it gives a very sharp image. Ref  and . I opted for the I2C bus for the display to keep it separate from the SPI bus controlling the ADF5355. I thought this wise to minimise noise transmission to the synthesiser. For a typical schematic of the of the OLED display module see .
To set the frequency and tuning step size Keyes type push button rotary encoders were used. These are widely available from the usual internet sources.
Two encoders were used, one as the main tuning control and the other to select the step size. The push button functions were used to select preset frequencies in each of the amateur VHF/microwave bands and to set the output power level.
The module I used is shown below. It used a 125 MHz reference oscillator with a push-pull output as that is claimed to improve the phase noise (PN) performance. For this application I used a external 100 MHz ovened reference for better frequency stability and accuracy. To provide a push-pull reference input to the board I supplied the reference via a small trifilar wound bulun transformer constructed using a double hole ferrite, connected to the REF+ and REF- inputs. To disable the onboard reference and connect the external one I had to unsolder L1 and populate R17 and R8 with 100pF capacitors. The schematic is available in the references at the end .
The ADF5355 gets its very high frequency resolution by using two fractional parts along with a programmable second modulus to set its frequency, (The first modulus is fixed in hardware). Frac1 is a 24 bit number and Frac2 is a 14 bit number. A good description of the process used to calculate the two fractional parts and the second modulus is given by Andy Talbot G4JNT in [ 2 ]. The Programme calculates these values from the frequency dialed into the OLED display and loads them into the appropriate registers. To have resolutions of the order of Hertz the micro controller must be capable of eleven decimal digits. The SAMD21 is a 32 bit device so when used with double precision arithmetic it is up to the job.
The code is available from Github as detailed below. To compile the code and upload it to a SAMD21 board start the IDE running and in the Tools menu select “Arduino/Genuino Zero (Native USB Port)” as the board. It may be necessary to install the software for this if it is not already there. To do this go to Tools > Board > Boards Manager and select “Arduino SAMD21 Boards (32 bits ARM Cortex-M0+)” to install support for the board. The signal generator code can be downloaded from here on Github, .
The finished unit
The outcome of this project is a signal generator with continuous coverage between 52 MHz and 13.6 GHz in 10 Hz steps. The step size can be changed in decades from 10 Hz to 1000 MHz. The display is an I2C OLED device which gives a bright well defined image. By adding amplifiers after the outputs from the chip the output power is boosted to useful levels for testing purposes. In terms of phase noise and spurious signal output it is not a match high end professional units but it sure beats then on cost, size and weight!
Addendum 1 - Using a Maple Mini Microcontroller instead of the SAMD21
Initial work on this project was done with the WeMOS SAMD21 board. This board is relatively expensive at around £8. A lower cost alternative is a Maple Mini board. These are around £3 and sport a 32-bit STmicroelectronics STM32F103CB ARM Cortex-M3 128k Flash, 20k RAM processor and are very adequate for this project. The pinning is different from the Atmel SAMD21 and there are slight differences in the code and the schematic. The code for the Maple Mini is available at  and the schematic showing the connections is below.
Recently a small vector network analyser (VNA) has become available on the usual auction sites from China. It started life as a kit aimed at hobbyists in China but has evolved into a product that has been widely “cloned” and made available for sale. There are a large number of sellers and apparently several different manufacturers. However at a cost in the £30 to £40 they seemed too good a bargain not to get one! Some of the clones are better than others and it is hard to judge which one you will get when you order one. I bought one from a Chinese seller on Ebay. It was version 3.1 of the PCB and broadly conformed to the boards designed by Hugen79.
The design makes ingenious use of low cost consumer ICs to produce a VNA that is capable of giving useful results up to 900MHz. The block diagram is below:
The heart of the unit is an audio codec chip that takes as its inputs the outputs from three SA612 mixers. The mixers are fed with a common local oscillator signal and their outputs are the reflected signal from the DUT, a reference signal and the transmitted signal through the DUT. The mixer inputs are the common local oscillator and:
- The reflected signal sampled by the bridge
- The reference signal
- The transmitted signal from the DUT output
The test signal and the local oscillator are generated by a Si5351A clock generator chip and are spaced by a constant frequency difference in the audio range of 6kHz (or 10kHz with some firmware versions). The three mixer outputs are I and Q signals at a 6kHz (or 10kHz) intermediate frequency, which are digitised in the audio codec chip to provide three data streams to the STM32F Microcontroller which computes the display data to present on the touch screen.
The Si5351A data sheet specifies its maximum output frequency as 200MHz but the designers have found that in practice most of the chips are able to operate to 300 MHz. As the outputs from the clock generator chip are square waves they are rich in odd harmonics and by generating LO and test signals whose third harmonics are spaced by 6 kHz it is possible to extend the frequency range to 900 MHz.
Extending the Frequency Range
Over the past year newer versions of the firmware have appeared on Github and the Nanovna IO group that extend the frequency range of the unit up to 1500 MHz by using the fifth harmonic of the Si5351A output. I was curious to see how well it would work and so I re-flashed the firmware in my unit with the DFU files uploaded to Github by Dislord, .
There are extensive guides to flashing firmware to STM32F microcontrollers on the internet and Youtube so I will not cover it here.
On calibrating my unit set to a span of 100 MHz and a centre frequency of 1300 MHz the results were not encouraging. A 50 ohm load on a Smith chart plot looked a bit like a sizable hedgehog jumping around on the middle of the chart which was not good.
Looking at the schematic revealed that there is a switch mode charge control IC (IP5303) to control the charging of the single cell LiPo battery and also provide the 5 Volt supply when running off the battery. This was a prime suspect as a source of noise. A clue was that the noise was worse when running on battery. Looking at the signal at the CH0 port with a spectrum analyser revealed that it was noisy. Taking the back off the unit and probing with a ‘scope showed that there was noise on the 3V3, VDD rail powering the microcontroller and the Si5153A. Adding a 33uF 16V tantalum SMD capacitor to the 3V3 rail, across C4 on the schematic(link) Vdd rail reduced the noise on the RF signal at the test ports suggesting that the source was switching noise from the IP5303 modulating the Si5153A output. This did not have an immediate effect on the noise on the trace and attention turned to the 5 V rail powering the three SA602/612 mixers. This showed several 10s of mV of noise and two further capacitors were added across this rail. Firstly a 33 uF SMD tantalum type was placed on the track leading to the 3V3 regulator and a 220 uF 10 V electrolytic type was placed across C49 on the 5 V output of the IP5303. The positions of the three capacitors are as shown in the two pictures below:
This was found to reduce the noise on the traces considerably suggesting that it was getting in via the power rails to the mixers. I also added tinplate screens over each of the three mixer channels to improve isolation but overall I did not find this made a significant difference. Overall after the addition of the screens and the extra decoupling the unit I have gave the following performance:
S21 Dynamic Range
S11 Dynamic Range
Some Results of Calibration at 1300 MHz
50 Ohm load
A Simple Reflection Measurement of a 23cm Antenna
The following two pictures show an S11 measurment of a WA5VJB 1290 MHz "Big Wheel" PCB antenna over a frequency range of 1250 MHz to 1350 MHz.
The "Big Wheel"
Overall the unit has become useful as an indicator of performance at frequencies in the 23cm amateur band and the additional capacitors have reduced the noise on the traces at frequencies in its original operating range improving the dynamic range there as well. There may still be some scope for further noise reduction.
Brian Flynn GM8BJF
04 May 2020