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From: charlesadi on 11 Apr 2010 07:47
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


From: Fred Marshall on 11 Apr 2010 20:35
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

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