SECTION 3: OSCOR MANUAL OPERATION
REI OSC-5000E 40
Demodulators
The F3 button in the Sweep or Analyze Mode can select the following demodulators:
FM WIDE: 250 kHz as used with FM Broadcast and TV sound channel
FM NARROW: 15, 6 kHz as used older technology two-way communications
SubCFM: uses 250 kHz primary IF and 15 or 6 kHz secondary demodulator
AM WIDE: 250 kHz used for fast scanning
AM NARROW: 15, 6 kHz used with AM Broadcast, short wave, CB, aircraft
SSB / CW: 6 kHz used with short wave, marine, amateur radio
Technical Notes:
DEMODULATING NARROW DEVIATION FM WITH A WIDE 250 kHz FILTER: The
OSCOR will sufficiently demodulate narrow deviation FM signals when operating
in the wide 250 kHz bandwidth. The automatic gain control will continuously
adjust the audio level to the correlator or headphones for optimum results.
WIDE DEVIATION FM WITH A NARROW 15, 6 kHz FILTER: If a narrow
bandwidth filter is used on wide deviation signals, over-modulation of the signal
profile and distorted audio will result.
USE OF THE PROPER DEMODULATOR WILL RESULT IN THE BEST RECOVERED
AUDIO--LOWEST DISTORTION AND LOWEST NOISE: Surveillance devices
using FM modulation will normally produce a small percentage of AM modulation
due to poor oscillator/buffer design, unregulated power supplies, or effects of
antenna/reflection.
AM modulated devices may also contain a small percentage of FM modulation
primarily due to an unstable oscillator.
Receivers also respond to FM signals with AM demodulation due to slope
detection against the IF filter skirts, and phase/group delay in the filter systems.
When receiving AM signals with FM demodulators, the imperfect limiting action of
an FM IF/demodulator will allow a small percentage of AM to also be detected.
Tuning Sub- Carrier
Sub-carrier demodulation is a means of decoding a second “piggy backed” signal
carried on a normal transmitted radio signal. This is sometimes referred to as double
demodulation. Sub-carrier signals are most commonly used for background music and
nationwide digital pagers. These frequencies normally fall between 50 - 120 kHz.
When a sub-carrier signal is suspected, you may perform a second demodulation by
activating the FM/SC demodulator, indicated on the display as SubC FM. Many
commercial FM radio stations and TV sound channels have sub-carrier signals that
typically contain MUZAK (elevator music), paging systems, or news stations.
To activate the Sub-carrier demodulator:
1. In the Analyze Mode, select the 250 kHz bandwidth using the F2 button.
2. Activate the Sub-carrier tuner by using the F3 button.
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