Re: [Discuss-gnuradio] Active Radar Hardware

[Daniel O'Connor]

On Friday 29 September 2006 07:30, Jason Hecker wrote:
> > lot more about it, and looking for better parts, but I've learned to ask
> > the experts early ;) Any ideas?
>
> I used to write software for a radar.  It used separate antennas for

I still do :)

> transmit and receive for several reasons though the RX and TX antennas were
> located right next to each other.  This arrangement works very well.  If
> you are concerned about too much power entering the RX stage you could use
> a switchable attenuator using a voltage signal and PIN diode.  Actually, if

We make MF & VHF systems and for some of our VHF systems we use a single set 
of antennas and a T/R switch (passive and active). However since our 
frequency of operation is 2-3 orders of magnitude lower it's probably all 
different...

> you want any sensible readings and a signal that has good dynamic range at
> the ADC you will need a controllable attenuator that increases the RX gain
> over time (in a logarithmic way) as the return signal gets weaker with the
> squared square of the distance (R^4 !).  You'll always get overload signal
> for a certain close-in range anyway.  Not much you can do about that.

For boundary layer/troposphere radars we halve our effective PRF and transmit 
a short low power pulse and listen with a low gain setting on even pulses and 
a high power long pulse with high gain on odd pulses. The sampling 
configuration also alternates to sample low and high.

I guess the other possibility is being adaptive, ie adjust your power/gain 
based on what you can currently see.

-- 
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
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