Hi Dave,

I've got to ask: why do people use marine radar on cars?!

I have a real tendency to have too many irons in the fire, and I'm very
busy right now, so this will have to go on the "long term projects" list.
However, I had some ideas on how it might be done relatively cheaply.

First of all, my primary interest was toward the aircraft side (I think
it would be REALLY amazing to have a display on your computer screen in
real time of all the aircraft in, say ,a 30 miles radius!) so my ideas
may not be as relevant to the weather version, although that interests
me, too.

I was thinking of using a bunch of Mini circuits ERA amplifiers in
parallel (with hybrids to combine power) as the output amp, providing
only around 100mW depending on how many I wanted to parallel.
Since these can be had for only a few dollars a piece and go up to about
20mW power. Some similar parts from minicircuits would also
make a nice LNA for the receive side.

I would mount an upconverter and a downconverter right up on the back of
the antenna (probably a small dish). I would feed the TX signal and RX
signal to/from the converters with regular coax, using a baseband of
about 1 MHz. Since A to D and D to A converters can easily sample at several
megasamples/sec, the outgoing signal could be generated by a D to A
connected to a high-speed DSP chip, and the incoming signal could be
processed by an A to D and another DSP chip. This way, a change of coding
scheme or decoding algorithm would be only a software change. I'm fairly
certain this would work for simple pulses, but I'm not sure if DSP chips
have enough horsepower for doppler extraction from pulse compressed
coding schemes (like Barker codes) which we might need to make up for the
low output power.

Finally, some PICs could be used to control steppers or other servos to
tilt the antenna horizontally/vertically. I was thinking of using
something around 5GHz, so a relatively small dish (perhaps a 2 to 3 feet
diameter) could be used.

Sean


On Sat, 4 Aug 2001, David VanHorn wrote:

> Ya know...
> A microwave-inclined storm-spotter like me might be interested in such a
> project.
> Lots of microcontroller room here, controlling the antenna and such.
> Lots of interesting analog stuff too.
>
> How to begin though?
>
> NWS is complaining already, about interference from people using marine
> radars on cars.
>
>
> --
> Dave's Engineering Page: http://www.dvanhorn.org
>
> I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here
> in my signature line, but due to the inability of sysadmins at TELOCITY to
> differentiate a signature line from the text of an email, I am forbidden to
> have it.
>
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>
>
>

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