> Communications and rf is my speciality, although I'm not familiar with
> the specific rf signature that the human body produces.
>
> If I can find some info on it, it makes my job much easier.
>
> Is '20 to 30' referring to VLF in KHz or MF in the 20 to 30 MHz range???
>
> I'm guessing that it's in the KHz range as a Doppler radar in the MHz
> range would produce bounced signals, which are likely to mask the body's
> rf signature and make it more difficult to detect.

The 20 to 30 was Hz.!!!
ie that is the Doppler modulation rate which you get when you mix
transmitted and received signals. The joint must oscillate slightly or
"burr" at around this frequency as the joint moves.

The RADARs used were the Philips Gunn diode door al;arms that were
very popular before PIR became common.

Low cost Doppler RADAR can be implemented with a transisor oscillator
i the 10's to 100's of MHz range - probably with a simple mixer
receiver.

Long long long long ago "Wireless World"  (I think it was) did a
Doppler RADAR intruder alarm using roll-your-own transistor based
TX-RX.

The vehicle RADAR project from Silicon Chip Magazine a year of few ago
may also have a suitably simple low cost circuit.

For person detection the range can be very short.

There is no certainty that the system I suggest actually works BUT the
history of the company who told ne about it suggests that they were
"real" and that they thought it worked.
The people doing this noted that it would allow you to differentiate a
person and avoid false signals from a flapping curtain, falling boxes
or a cat - all objects which would otherwise trigger a RADAR based
unit. This may be common knowledge and it may be on Google OR it may
be 'specialist knowledge' which they used and nobody else did. The
company was "Medical Telectronics ltd" and they said they arrived at
this solution by asking  biodmedical specialists in the NZ public
hospital system what signals might uniquely identify a human body.

It appears that the company is long long long gone
http://opencorporates.com/companies/nz/75086
It also appers that they were associated with the Australia
Telectronics company who were early Pacemaker developers - and whose
buyers lost vast amounts of money in legal settlements when a
technically minor but minor but medically crucial problem occurred.
http://en.wikipedia.org/wiki/Telectronics


         Russell
--=20
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