DETAILED CPM-700 PROCEDURE
25
REI
CPM-700
PHONE/LINE RF SWEEP
To test a telephone for RF transmitters, measure the signal strength of the
instrument and line when in an “off hook” (in-use) condition. Listen for a
dial tone through the headphones to verify a phone bug. You may turn off
or lower your Known Sound Source for this sweep since the telephone
provides a dial tone and/or messages. If a long recorded message service
is available, such as a business report or farm market report, use one of
them as a Known Sound Source to disguise your actions.
1.
With the CPM-700 next to
the phone and the phone
on hook, shorten the
Probe’s antenna to
approximately four inches
(10 cm) to reduce
ambient RF reception.
Wrap the curly cord from
the handset around the
antenna at least four
turns.
2.
Compare the previous
room levels to the
measured (on hook) phone levels. If there is a substantial increase
on this test an audio verification is necessary to determine if it is a
“friendly” signal (possibly short-wave signals) or a phone powered
room transmitter.
3.
While noting the nominal RF level on the bar graph, lift the
handset off the hook and look for an RF level increase (normally
more than two segments). Listen for a dial tone through the
Headphones. If the bar graph level increases or if a dial tone is
heard in the headphones, this indicates a possible bug. A normal
phone will cause only a small pop sound and a momentary jump
in the bar graph.
4.
Check the telephone instrument by repeating the above tests with
the probe by the side of the telephone. Measure the difference
between on-hook and off-hook. Listen for a dial tone.