LIVINGSTON COUNTY
AMATEUR RADIO PUBLIC SERVICE CORPS

(Revised 12/16/1999) (Revised 6/12/2003)
Tim Conroy, Digital Operations AEC
 
 

INTRODUCTION TO DIGITAL COMMUNICATIONS TECHNOLOGY
Livingston County Amateur Radio Public Service Corps (LCARPSC)


 

LCARPSC currently uses 3 digital modes: packet, pactor, and CW. Each mode has its own advantages.

Packet and Pactor

Packet and pactor interfaces amateur radio to a computer terminal through the use of the terminal node controller or TNC. The term packet refers to the fact that digital information is sent in packets that are related to the TCP/IP protocol used on the Internet. In fact, the development of packet in amateur radio was patterned after the TCP/IP protocol used by the Internet. Pactor is a specialized use of packet.

There are a number of advantages that packet and pactor have over other modes of communication in amateur radio.

1. Amateur radio packet uses a similar error correction scheme that the TCP/IP protocol uses. That is, when the packet is received it is acknowledged by the receiving station with check sum information sent back to the transmitting station. If the check sum is incorrect the packet is re-transmitted. If for some reason, e.g. weak signal, QRM, QRN, etc. a correct check sum cannot be achieved after 10 tries, the TNC's will automatically disconnect. With packet you either make it accurately and correctly, or you don't make it at all. VHF packet at LCARPSC is 1200 baud and pactor, which is only used on HF, adjusts itself to band conditions to 300, 200, or 100 baud. Pactor is often able to pass traffic the HF Packet could not.

2. With packet (HF or VHF) many stations may use the same frequency (almost) at the same time. That is, if packet communication is already occurring on a given frequency it is perfectly all right to connect to a different, or the same, station. TNC's are set up not to interfere with one another. With our new modern amateur packet protocols, packet collisions (i.e. two packet stations transmitting at the same time) have been greatly reduced. Even while connected a packet operator can monitor activity on that frequency. This is helpful during ARES/RACES alerts. With pactor only the 2 connected stations may use the frequency.

3. Packet stations may be digipeted (simplex digital repeating) or linked via nodes thus, allowing accurate and reliable communications over great distances. With pactor, digipeating or the use of linked relay nodes is not possible. The major advantage of HF pactor over HF packet is that it can get the traffic passed in poor band conditions that HF packet cannot. HF packet requires a good clean signal to copy. The major advantage of HF packet over pactor is, packet can be relayed over by digis and nodes and multiple connects are possible on the same frequency.

4. A capture file is created for all connects thereby providing a written record of any communication.

5. Packet and pactor radio may connect via radio to the Internet.

6. Packet and pactor messages may be received when operators not immediately present.

7.Packet and Pactor message may easily be printed.

8. During ARES/RACES activations remote packet or pactor stations may be set up with relative ease, and operators with relatively little training may send large volumes of information back to EOC.

9. LCARPSC may connect directly to the State Emergency Operations Center (SEOC) in Lansing, or during a time of disaster to any alternate SEOC designated.

11. Amateur packet radio may use specialized software for the Automatic Position Reporting System (APRS). LCARPSC uses WinAPRS, the most sophisticated and up-to-date APRS software available. WinAPRS is networked to the three LCARPSC computer consoles at the Livingston County Emergency Operations Center. With WinAPRS we can:

    A  Track mobile stations down to street level within 15 feet.
    B  Instantly view weather alerts for our county and all other counties in our region
        as they are sent by the National Weather Service.
    C  Observe weather information automatically collected and reported by other
         stations, especially those stations to the west of our county.
    D  Send messages to other stations on frequency.
    C  Send email messages via the Internet.

11. The 2 main disadvantages of non-CW digital modes are: 1. They require a reasonably strong signal and/or QRN or QRM free. 2. Channel congestion during emergencies can slow or stop digital.

CW

CW stands for continuous wave, it is usually the keying and unkeying of a radio transmitter. CW is the oldest communications mode in amateur radio. CW was around long before digital modes were even conceived. It is the only digital mode that can interface directly to a human being without the use of digital equipment. CW is primarily used for high frequency communications.

There are a number of advantages CW has over other modes of communication in amateur radio.

1. While the practical use of CW requires a highly skilled and highly experienced operator, CW works under the worst of conditions when no other mode of communication will work. This has been demonstrated time and time again. National Traffic System (NTS) CW nets operate under conditions that make it impossible for NTS phone nets to operate.

2. In most cases, CW is more efficient than phone for handling written message traffic.

3. Although CW cannot compete with packet there are some situations where packet cannot be used.

4. At LCARPSC we have an efficient high frequency antenna and transceiver. We have an automatic keyer and paddles for CW. We can also transmit and, under reasonable conditions, receive CW on computer console C via our TNC.

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