Radio Shack ADV0801 Owner's Manual page 82

ADV0801 Owner's Manual Draft
This means that the transmitters and receivers operated in one licensee's radio system may be
close enough geographically to another licensee that it is technically possible for the two
licensees to hear radio traffic from each other's system. This is especially true for business radio
users, however, it is not all that uncommon for different public safety licensees to be close
enough to each other for one licensee's radio traffic to be heard by another licensee. Additionally,
certain radio propagation events can sometimes allow radio signals to travel hundreds or
thousands of miles beyond a licensee's service area, in some cases, making their radio
transmissions receivable on the other side of the continent.
Reception of traffic from another radio user can be an undesirable situation, causing confusion
and distraction.
Selective squelch is employed in transmitting and receiving equipment to limit reception to only
those transmitters that are transmitting the correct encoded selective squelch signal. Much in
the same way that a radio licensee can use selective squelch to block out foreign traffic from
their radio receivers, you can use selective squelch on your ADV0801 to block undesired traffic
from being received on your scanner. In addition to this basic selective squelch capability, your
ADV0801 can search for and display the selective squelch type and squelch tones or codes in use
on a particular frequency.
The three types of selective squelch available in the ADV0801 are as follows:
CTCSS
CTCSS stands for Continuous Tone Coded Squelch System. In CTCSS, the transmitter sends a
special, low level audio tone continuously while a transmission is in progress. This is known as
a subaudible tone - the level and frequency are such that they are difficult or impossible to hear
in a receiver's speaker. The receiver (or your scanner) will detect and decode this tone, and if it
matches the programmed tone, the speaker will be unmuted and voice audio allowed to pass. If
the tone is not present, or an incorrect tone is found, the receiver will remain muted.
Additionally, the ADV0801 can detect the CTCSS tone that is in use on a transmitter, and will
allow you to store the tone value with a CONV object when a CTCSS transmission occurs.
It is possible to hear this tone if you listen with headphones. CTCSS sounds like a low, steady
"hum" in the background of a voice transmission.
DCS
DCS stands for Digital Coded Squelch. In DCS, the transmitter sends a special, low level data
signal continuously while a transmission is in progress. This is known as subaudible data - the
level of the data signal is such that the data is difficult or impossible to hear in a receiver's
speaker. The receiver (or your scanner) will detect and decode this data, and if it matches the
programmed code, the speaker will be unmuted and voice audio allowed to pass. If the DCS code
is not present, or an incorrect code is found, the receiver will remain muted. Additionally, the
ADV0801 can detect the DCS code that is in use on a transmitter, and will allow you to store the
code value with a CONV object when a DCS transmission occurs.
It is possible to hear this tone if you listen with headphones. DCS sounds like a low "purring" in
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