Dial Up Access
Accessing remotely located communications receivers creates
unique challenges for the radio system operator. Remote access to receivers is
frequently required in the public safety, law enforcement, intelligence,
military, two-way and broadcast communities. By locating a radio receiver at a
remote site, the coverage area can be extended beyond the existing radio
horizon. The optional Scan*Star modem feature adds support for accessing
remotely located radio receivers via dial up modems.
DSVD Modem Support
By default, the Scan*Star modem feature is configured for the
This model is capable of transmitting data and audio simultaneously over a
single dial up connection. Other modem types can be configured as well.
At the remote site a radio is connected directly to a modem.
The modem is configured to automatically answer incoming calls, and allows the
base station to send commands to the radio and the radio to send signal data to
the base station. When a DSVD modem is used, received audio is also relayed to
the base station.
The base station modem is managed by the Scan*Star software.
Calls to distant receivers are originated using Scan*Star, and received audio
coming from DSVD modems is connected to the PC sound card input.
The base station maintains a list of telephone numbers for
remote sites, and allows the operator to choose a remote site by name.
Automatic Delay Compensation
Modem connections over the public switched telephone network
experience significant delays in transmission between the remote radio and the
base station. Round trip delays of several hundred milliseconds are typical.
Satellite or intercontinental connections can have delays of several seconds or
more. While rarely a problem in voice calls, these delays limit the maximum
To counteract the effects of transmission delays, the
Scan*Star modem option software measures the delay and adjusts the scanning
speed (as well as other critical timing parameters) to compensate. Some
receivers can not be operated remotely using the DSVD modem approach.