This RF Wave Absorbion meter will detect signals
between 10cms and 10m away all acording
to the setting
of the 22MegOhm gain adjustment potentialometer and the power of
the transmitter. The RF signal is detected across the germamium
OA91 doides and rectified to a d.c. level driving a 10LED driver IC. The LED's are marked 1 to
10 indicating the strength of the
detected RF signal. You can also
connect a 250uA moving coil meter across
the preset fixed connections, enabling smaller signals to be detected i.e signals lower
than 30mW at 5 feet. This circuit
is ideal for tuning up low
power transmitters or locating hidden
transmitters. If a specific frequency band is required, replace the OA91 diode that goes
to negative with a parrallel tuned circuit as
indicated. For 27MHz
L=10Turns and C=39PF, for
50MHz L=7turns and C=27pF, for
80MHz L=5turns and C=12pF, for
110MHz L=4turns and C=10pF, for
150MHz L=3turns and C=8.2pF and for 180MHz L=2Turns and C=2.2pF. All coils are 22SWG wound on a 10mm air former.
Forrás: AJP
circuits