Re: Detection of portable recorder
Ken Carrigan ( (no email) )
Mon, 12 Apr 1999 20:42:06 -0400
The problem with this is the signal to noise ratio, and the
sensor to pick up the field. The sensor is the key part. With
low frequencies being used, a loop antenna tuned to the particular
frequency would be needed. Then a very selective narrowband
filter (5 stage) and low noise preamps with compander circuits and
possibly noise cancellers for 60/50 Hz. Can even use phase lock
loops to track the recorders 'varying' motor drive, or erase head
oscillator.
With TV scambling, much easier. Just use the IF frequency of
the receiver and blast away!! Most TV's are highly sensative
to this frequency and will wipe out any and all channels due to the
local oscillator downconverting to the IF (4.5Mhz)?
v/r Ken Carrigan