Microbit RRC-1258 MkII(s) Manual de usuario descargar pdf (Pagina 25)

119

D Star

deals on the purchase of a repeater if a number of radios were bought,

which allowed clubs and individuals to enter into negotiation with those

in a locality to take up the offer. Today, however, there are many more

ways of joining the network. These will be discussed further on in the

chapter, but now include the DV Node Adaptor, DV Dongle and DV

Access Point to name but a few.

D-Star modes

D-Star carries digitized voice and digital data, but it does the job in two

different ways, there being a combined voice and data mode (DV) and

a high speed data only stream (DD).

Although data and voice are carried at different rates and are

managed in different ways, they are transmitted as packets. The D-

Star protocol is therefore similar in some ways to the Packet Radio

(AX.25) protocol that allows the exchange of data between Terminal

Node Controllers (TNCs) or the Ethernet protocol used by home and

business computers.

The AMBE codec was mentioned earlier. It can digitise voice at

several different rates. D-Star uses 2.4kbps (bits per second). In

addition, AMBE adds information to the voice data that allows the

codec at the receiving end to correct errors in the transmitted stream.

The result of the overhead is that the digitized voice stream carries

data at a rate of 3.6kbps.

Simultaneously to the digitised voice, DV Mode (low speed data

mode) can also carry 8-bit digital data at 1200bps. This data is un-

modified when transmitted, so it is up to the operator’s software to

manage the flow of data whilst it is being exchanged.

When operating in DD Mode (high speed data mode), the voice

signal is unused and all packets are dedicated to the use of digital

data. Transmitted data is sent as raw data at a rate of 128kbps. Like DV

mode, this is transmitted with no modification, the flow control being

undertaken by the software package chosen by the user. In DD mode

the net data rate is comparable to or better than a high-speed dial-up

Internet connection.

How D-Star works

Being a packet based protocol, D-Star data is processed and

packaged using the required data and additional information.

Packets are sent in their entirety and are processed as a group by

the receiving station.

An important difference between AX.25 Packet Radio and D-Star

is that AX.25 requires an acknowledgement and the TNC at the

1 2 ... 20 21 22 23 24 25 26 27 28 29 30

Sin comentarios

Microbit RRC-1258 MkII(s) Manual de usuario Pagina 25