FMCW Radar help required.

Hi All, 
For an FMCW Rdar I plan to provide a 100us ramp to sweep 300MHz . I get an
(IF) of 40Khz for a distance of 1meter . My Gunnplexer datasheet shows an
(IF) band width of no more than 5000Hz . Then how is it possible to capture
40Khz (IF) ? .


Charles 

charlesadi wrote:
> Hi All, 
> For an FMCW Rdar I plan to provide a 100us ramp to sweep 300MHz . I get an
> (IF) of 40Khz for a distance of 1meter . My Gunnplexer datasheet shows an
> (IF) band width of no more than 5000Hz . Then how is it possible to capture
> 40Khz (IF) ? .
> 
> 
> Charles 
> 
> 

Dunno... maybe it tracks?  That might well explain it.  But, I didn't 
try to follow your numbers.

1 meter would have a round trip time of 2m/300,000,000m/sec, or 
2m/300m/usec = 0.006666usec or 6.6666nsec

300MHz/100usec = 3MHz/usec

So, 3MHz/usec X 0.006666usec = 0.02MHz or 20kHz frequency difference 
between transmit and receive for a ramp.  So maybe we get the same 
numbers when one if it's a sawtooth instead of a ramp?  AND it has to 
track the transmit frequency at that!!

Now, if the range is relatively fixed at 1m then the return is going to 
be 20kHz and then -20kHz but outputting the same range.

But then, only you have that datasheet.....

Fred