[hpsdr] VHF/UHF downconverter for HPSDR

[Ante Vukorepa]

On srijeda, 21. rujna 2011. at 23:18, Ante Vukorepa wrote:
> 1) using Si570 (high grade LVDS version, if possible) as the LO to feed a high IP3 Mini Circuits frequency mixer, then filtering out the higher "image" with a 500MHz-ish low pass filter
> B1 is probably the best option for initial experimentation and my own (not very demanding) purposes. So that's the route i think i'll go, as soon as i catch some free time and start putting all this down on paper. My plan is to try and design a down converter consisting of fore-mentioned elements (Si570, frequency mixer, filter) plus a microcontroller, that would fit an Atlas card and would be controlled through the bus, via I2C. The vision is to have the ability to bypass and turn all the elements, including the microcontroller, off when not in use, so the impact on the existing HF signal chain is minimal.

I've put together an initial block diagram for what i've had in mind:
http://dl.dropbox.com/u/1702513/Block.png

The board will be 2-layer if possible (to simplify and cheapify things initially), with one side dedicated almost purely to ground (separate analogue and digital ground planes, of course, perhaps even a completely separate plane for the Si570). Omron SMD signal relays will be used for pre-amp and filter bypassing and oven control (control in the sense of having it completely on or off, not in the sense of PWM). An Atmega168 or 328 will control both them and the Si570 providing the LO frequency. The Atmega will, in turn, be controlled via an I2C or SPI line, by the other boards on the bus, or manually, via a front control panel consisting of a rotary encoder, LCD and a few buttons. The balun is there to convert the differential Si570 CML output and suck out as much decibels as possible to feed a high IP3 frequency mixer. The (optional) FM broadcast band-stop filter is there to kill the interference from strong nearby FM towers, if needed.

How am i doing so far?

-- 
Ante Vukorepa
Sent with Sparrow (http://bit.ly/sigsprw)

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