NNTP-Posting-Date: Sat, 19 Oct 2002 19:56:49 -0500
From: "Dave VanHorn"
References: <email@example.com> <5HGdnaFia_mUHC2gXTWc3A@comcast.com> <firstname.lastname@example.org> <email@example.com>
Subject: Re: Radar basics?
Date: Sat, 19 Oct 2002 19:56:49 -0500
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> > Homodyne dopplers don't know distance, and if you rotate the antenna,
> > will tell you they are seeing motion, because effectively, you're moving
> > world. :)
> Hi Dave, not all radars are pulse radars. CW radar is common in the
> military, you can get distance by adding some low frequency modulation
> and measuring the phase shift on the returning signal.
That's why I used the quotes. The field disturbance sensors were marketed
years ago as "radar" alarms, but they never had any concept of direction or
range. "RADAR" is about getting direction and range, no matter how you do
it. FD sensors can't tell the difference between a roach at 6" or a truck
at 20'. And that's mostly why they aren't used anymore for alarm systems.
People always set the gain controls to "max" because obviously more is
better, then they get mad when the system falses. PIR was a wonderful
change, when it was introduced in the 70's finally a sensor that you really
have to try, to screw up.
This sensor that they were discussing at the start of this thread, is almost
certainly an FD sensor.
Bulldog markets them for car alarms, I think in the 2.3G range. I have a
couple on hand.
They used to be done down at 900 or so. for home use.