Introduction, and new project description

Clifford Heath
 

A few of us locally (Sydney/Melbourne) are starting a design for a $100 SNA/VNA
using the AD9959 quad-DDS module, which is good to 200MHz (500MHz core).
The design will use an Arduino with a touch-screen LCD, and an AD8302 gain/
phase chip. This will provide an indication of phase as well as amplitude, though
the phase is not terribly accurate. The main benefit from going with the AD9959 is
extending to 200MHz and having four channels, with digitally controllable phase
shifts. The unit will embed a USB power pack to make it portable, yet easy to charge.

We plan to extend it to a VNA following the path of <http://n2pk.com/VNA/VNAarch.html>,
who added a mixer, DC filter and 24-bit ADC to an I/Q signal generator. That part of
our circuit will be implemented with a large input bandwidth (1GHz) to allow use of a
higher-frequency LO (e.g. ADF4351) to act as a direct-conversion spectrum analyser,
though we have to investigate switchable filter options for that to work well.

Another member of the group wants to use an STM32F4 instead of the Arduino, to
allow low-IF SDR and spec-an, perhaps 100KHz bandwidth. So that's also a possible
path.

During my research for this design, I found the PHSNA and joined the group; though
I've already implemented something similar before finding PHSNA.

I just thought I'd mention the project to see what interest exists.

Clifford Heath, VK3CLF, http://github.com/cjheath

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