This project is an entry level 47 GHz transverter. An experimenter’s station. The design philosophy and construction are presented in detail. The two major components of the 47 GHz transverter, the SDR IF system with a flexible choice of IF frequency and the mixer block with associated LO for a 47 GHz transceiver, are described in detail. This entry level transverter is suitable for short range QSO’s with simple antennas. The overall approach capitalizes on an existing SDR IF transceiver, and on basic and affordable uWave and mmWave components. The components are the minimum equipment needed to put a transverter on the 47 GHz band. Of course, the SDR based IF radio isn’t a necessary part of the 47 GHz transverter project, but does continue the SDR theme of my station. The resultant 47 GHz transverter is a foundation for mmWave experiments and further station development.
At present, most amateur mmWave communications are limited to arranged, relatively limited distance, terrestrial paths. For most amateurs, relatively simple, entry level equipment provides plenty of opportunities for learning and experimentation. High power and low NF receivers are nice but not necessary. Affordable radio components for this part of the spectrum are difficult to source. Heroic efforts at EME communications and record breaking terrestrial QSO’s are best left to the talented few that have the knowledge and resources for these activities. This transverter project is designed to help the interested amateur get on the air, learn the basics of mmWave operation, and begin the journey to further station development. A beacon transmitter, in addition to the transverter, is included in this project. The beacon transmitter provides a signal source for transverter tuning and mmWave experiments.
SDR IF System
As previously described, SDR as flexible IF system, an advanced microwave SDR is very flexible IF system, ideally suited to the need of an experimenter. The advanced SDR can be configured to provide just about any functionality that might be useful to the mmWave experimenter. The SDR can provide IF capability at any frequency within the 50 MHz to 6 GHz range. Thus the experimenter isn’t limited to the traditional VHF IF frequencies. The builder can instead choose UHF and microwave frequencies for an IF, frequencies that suit the desired mmWave conversion scheme and available parts. The flexible IF capabilities of the SDR IF, when paired with a microwave transverter such as the 10 GHz transverter in this project, can be extended even further: SDR IF system for upper microwave and mmWave bands SDR software typically features the panadapter and waterfall displays which are useful for signal locating and for quantifying relative power measurements for experiments. The SDR can be programed to demodulate any modulation the user may choose, such as digital modes, SSB, CW, FM, etc.
Transverter: LO and Mixer Block
RF components for mmWave radios are difficult to find. The experimenter must be flexible and imaginative. This project is built with components that I have been able to locate. However, the same transverter design principles can be implemented with alternative components that are available to you.
The 47 GHz transverter is based on the superheterodyne principle, the same principle of frequency conversion that is ubiquitous for familiar radio systems in the HF through UHF spectrum. No magic here, just a normal mixing scheme that uses special miniaturized components that function efficiently at mmWave frequencies. This project uses the basic superheterodyne equation for a 47.0881 GHz multi-mode transverter. An LO of 12.2400 GHz is multiplied by 3X in the multiplier to generate a 36.7200 GHz harmonic, the LO frequency for the mmWave mixer. An LO frequency of 36.7200 GHz with the 10.3681 GHz IF results in ‘high side’ mixing: 36.7200 GHz LO + 10.3681 GHz IF = 47.0881 GHz RF. In summary, the 10.3681 GHz IF transceiver mixes with the 36.7200 GHz LO to transmit and receive on 47.0881 GHz.
The heart of the transverter is the so called ‘Philips’ module, an integrated multiplier and mixer block that once was part of a 37 GHz commercial communication system. Adam, 9A4QV, published an informative article that describes his 47 GHz transverter built with this module: 47 GHz transverter Adam reverse engineered the module and described the internal circuitry of the multiplier / mixer combination. The multiplier circuit contains a low pass filter system that filters out multiplier outputs to the mixer diode to frequencies below about 37 GH. The low pass filter in the multiplier severely limits the LO drive to the mixer at LO frequencies much above 37 GHz. The mixer diode accepts a wide range of IF frequencies. I have tested this mixer with IFs ranging from 10 MHz to 10 GHz with good success. That said, for 47 GHz operation, this module works best with a very high IF frequency, 10 GHz in this case, due to the design of the multiplier / LO circuit. The multiplier / mixer module RF interface is via a WR28 wave guide port.
The transverter mixing scheme for this project is changed, from 4X multiplication in Adams example, to a 3X multiplication for this transverter. The IF is changed from Adam’s 432 MHz example to 10 GHz for this project. These two changes increase the LO drive level to the mixer and together improve mixer conversion efficiency. The operating input parameters are LO: +10 dBm, and IF: +10 dBm. The module DC input via a 10k current limiting resistor is 8 Vdc. Conversion efficiency is optimized by adjusting the multiplier and mixer bias potentiometers. Measured RF output is -35 dBm in the transmit mode. The receiver noise figure is unknown. The multiplier LO input and mixer IF input are drive level dependent. Substantial deviations from the parameters listed here dramatically reduce receiver sensitivity and transmit power output. The beacon transmitter, uses an identically configured second Philips module to produce the 47.0881 GHz beacon signal. The beacon LO and IF are supplied by two synthesizers instead of one synthesizer and a 10 GHz IF transverter as with the transverter.
The LOs for the transverter and beacon are based on the newly available, and relatively inexpensive Arduino controlled ADF 5355 synthesizer board. Greg McIntire, AA5C, published a paper in the Microwave Update 2017 Proceedings that inspired this approach: ADF 5355 Microwave Sources AA5C and here: Arduino controlled synthesizers The ADF 5355 synthesizer is controlled by an Arduino Due micro-controller. The synthesizer produces a 12.0240 GHz signal for the LO input to the multiplier. The native –18 dBm synthesizer output is amplified by a Mini-Circuits ZX60-183A+ broadband RF amplifier to produce > +10 dBm LO output to the multiplier. A precautionary measure to reduce potential digital and phase noise modulation of the LO signal, was to bypass each of the Arduino controller and ADF 5355 synthesizer boards Vcc lines with large value electrolytic capacitors. The LO is disciplined by an external 10 MHz OCXO, the same master clock for the SDR IF. With OCXO control, the transverter, beacon transmitter, and SDR IF all align such that the 47 GHz signal frequency is accurately defined.
The temporary mounting arrangements permit the various components to be removed and used for other projects, and easily reassembled for 47 GHz transverter operation. The large gray box houses the ADF 5355 based LO synthesizer. The silver cube is the ‘Philips’ multiplier / mixer module that is the heart of the 47 GHz transverter. The gray colored coaxial cable is the IF connection to the 10 GHz IF transceiver, located off the photo to the left: 10 GHz IF Transceiver The gray colored home made horn antenna was constructed from hobby store copper sheet mated to a salvaged WR28 waveguide flange.
The beacon transmitter visually appears more complex, only because the OCXO, beacon keyer, and 12 GHz LO are exposed, not included in the SDR IF enclosure for the transverter and not visible. The black box at the top is the 11 GHz IF signal source. At the bottom, the silver tin box houses a 12 GHz DL6NT LO from another project utilized here for the beacon transmitter LO. The silver cube on the right is the ‘Philips’ multiplier / mixer module that functions as the beacon transmitter and outputs to another home made horn antenna. The PIC controlled beacon keyer is located in the upper left hand corner of the photo. The OCXO is located in the lower left corner of the photo.
The transverter and companion beacon transmitter, when combined, provide a basic stimulus-response radio system that an experimenter can use to explore mmWave propagation and as a basis for further station development. There is much to learn about mmWave amateur radio. For example, home made horn antennas are depicted in the photos. There are ample opportunities to build and test alternate antenna types in pursuit of greater performance. The relative changes in real world performance can be quantified using the SDR panadapter display.
I found it interesting and enjoyable to observe and compare LOS, scattering, refraction, and reflection mmWave propagation in the shack. An example experiment was to observe more than 90 degree reflection of the 47 GHz signal around a corner. The passive reflector was a suitably positioned pizza pan. Other experiments are possible.
The optional station detail, the 10 MHz OCXO master clock, is worth discussing. All of the synthesizers and the SDR IF are sync’d to the 10 MHz clock. Syncing the oscillators, to align all the moving parts, is a major aid to positively define the operating frequency and to find weak signals in the noise. That said, despite the high quality OCXO master clock, a ‘feature’ of using multiplied low cost synthesizers as LOs, is abundant phase noise on the output and input signals. The close in phase noise is about 25 dB below the fundamental 47 GHz signal, low enough as to not detract from perfect SSB intelligibility and a pleasing CW note.
Note the prominent phase noise sidebands on both sides of the carrier. These sidebands are the result of frequency multiplication of simple synthesizer systems in the complete system LOs. Weak signal copy and signal quality are not affected in the intended application of this simple transverter.
This complete radio system, the transverter and beacon, could be a very useful aid to help other amateurs setup and tune rigs for the 47 GHz band. Defining the operating frequency with the disciplined synthesized LOs is also a helpful aid to make it easy to tune multiple rigs to the same frequency.