For many years I have wanted to build a receiver. Experimental Methods in RF Design
decribes a receiver called the R2Pro. Kit's of parts provided by KangaUS provided the
impetus to build an R2Pro. But, how to make the R2Pro cover all HF and some VHF bands?
The Local Oscillator quadrature generation over a wide frequency range was a problem.

This LO is a little different. Have not seen this application in the literature. Not
that it has not been done, I have just not seen it. Nor did I know if it would work!
So, why not try it.

It uses a PIC microcontroller and an AD9912 DDS. Frequency output is 1.5 MHz to 400 MHz.
Having said that, I can only test up to 200 MHz, the coverage of available signal generator.

The 9912 HSTL output is used. For those not familiar with the HSTL output - complementary,
1.2 volt P-P, square wave. HSTL specified frequency of 20 MHz to 400 MHz and up to 725 MHz
if the HSTL output doubler is enabled.
I have tested HSTL down to 8 MHz where the waveform started distorting.

The 9912 HSTL output is fed to Quadrature Generator that uses Micrel PECL IC's rated
at 3 GHz. Included on the Quadrature PCB is sideband switching and R/T switching.

The 9912-PIC PCB was obtained from David Brainerd, WB6DHW. The PCB mounts a Microchip
18F2550 microcontroller, AD9912 DDS and a MMIC RF amplifier(Not used in this application).
Unfortunatley, David no longer has this PCB available.
Schematic's and PCB for the quadrature geneator was made using Express PCB software.
The Auxilary Circuits were built dead-bug on a scrap of PCB material. The Serial-Parallel
Interface and Memory PCB was designed using Express PCB software and made using primitive
india ink/etchant method. 

The remainder of the receiver hardware is standard R2Pro modules obtained from KangaUS.

The control program is written in Microchip Assembly Language. Much more information about
the Local Oscillator operation is avaiable in the program listing.


How does it work? Opposite sideband suppression is in the 45 dB range from 160M to 6M.
No effort has been done to measure the phase difference between the quadrature outputs
and therefore make any corrections if the phase differences are excessive. This may be
done in the future.

The bad part of this LO is power usage and size. It is definitely not for backpack use.
The LO, including the DDS clock, OCXO and multiplier/amp, draws 1.2A @ 12 Volts!

This project was started in late 2010 and is a work in progress. It was fun trying
something I had not seen before and did not know if it would work. A very pleasant
suprise when the receiver worked.


Buck  KD8RRI