47 GHz Radio

My 47 GHz radio represents my most ambitious radio construction, one that took 3 years to complete and is still in a continual process of upgrade and improvement.

The outside of the 47 GHz radio and its hundreds of screw holes

After building a decent performing 24 GHz radio I set out to build a really decent 47 GHz radio.  My first 47 GHz radio consisted of an LO source and a crude home-made mixer.

This time, there are separate mixers for receive and transmit.  These mixers are subharmonic image-reject mixers made by UMS, and are bare GaAs MMICs.  The advantages of this architecture include the elimination of any filters on the transmitter output, and the need to generate an LO at 23.472 Ghz instead of 47.088 GHz.

47 GHz receiver detail

Working with bare dies requires some unique tools including a wire bonder, tiny tweezers, a microscope, and a wafer dicing saw to cut substrates.  In the picture above, there are small white ceramic substrates with gold stripes on them.  These are 50 ohm transmission lines and are made from aluminum oxide ceramic.  They must be cut to size and to do this I built a wafer dicing saw (writeup of the project at the Mightyohm blog) which includes a vacuum chuck to hold the pieces.

Dicing saw setup

A great deal of machining was done for this project including precision housings for the transmit and receive modules, as well as the rotary waveguide switch.

Machined parts of the 47 GHz radio

Machining was done using standard machining techniques as well as CNC wire and die sinker electrical discharge machining.

RF deck with waveguide switch and transmit interlock cam

In addition to the mechanical work, lots of electronics went into this radio as well.  A special voltage regulator board was built that provides numerous voltages required for the MMICs.  This board uses a switching regulator followed by linear regulators to provide good efficiency and clean output.  Any ripple on the DC lines would appear on the output as noise!

MMIC voltage regulator board

GaAs PHEMT transistors are depletion mode devices and require a negative gate bias voltage before the drain voltage is applied.  Otherwise they conduct on their own and could blow themselves up.  A sequencing and overcurrent protection board was built to take care of the delicate MMICs

MMIC sequencer and protector board

The Local Oscillator is generated by doubling a 12 GHz DRO synthesizer and mixing it with a 528 MHz signal generated by an early prototype of the OpenSynth PLL.  This is then filtered and becomes the 23.472 GHz for the transmit and receive modules.

Inside the 47 GHz radio

A 10 MHz ovenized oscillator provides the frequency reference for this radio.

47 GHz radio on the multi-band tripod

My best DX on this radio is 160 miles and I have worked 7 different grid squares from atop Frazier Mountain.


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