Dial Up Access Optional Feature

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.

By default, the Scan*Star modem feature is configured for the MultiTech MT5600DSVD. 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.

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 scanning speed.

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.