Chelmsford Amateur Radio Society Advanced Course (8) Operating Practices

Packet Radio Equipment required: Modest power Transceiver and aerial installation TNC In most cases a low spec PC will suffice Software Can send graphic pictures, files, software A single frequency can handle more than one contact at a time at 1200 baud, 9k6 or higher Message information is typed on keyboard, passed to the TNC, converted to data packets which are sent out as audio for transmission over the air. On reception the TNC converts the audio tones back to data and reassembles the message

Packet Mailboxes etc Direct contact with local packet Station or further a field via nodes/digipeaters Mailboxes/BBS: Messages input into BBS (GB7/MB7 callsign) and stored for local access or forwarded via other BBS’s. An NoV is required to run a BBS Each message has the senders and recipients callsign. Messages are automatically routed from host to the recipients BBS. The recipient is alerted to receive message Frequencies used usually VHF, UHF and Microwave, but could be HF, undersea cable or satellite

Packet DX Cluster The DX Cluster distributes DX information to other Amateurs in near real time, locally and around the world Amateurs place their spots or information on the cluster to benefit others who are logged in, who can see for example where the DX is and in what band. Can be accessed via radio or internet . It’s a team effort with Amateurs helping each other

Repeaters Repeaters are intended to extend the coverage of stations Can have Voice, TV or Internet links

Repeaters & Offsets Repeaters have a frequency shift between Input and Output so they can transmit at the same time as receiving and have ‘Logic’ for control , Morse idents etc On 2m Shift is 600kHz, On 70cms Shift is 1.6 or 7.6MHz The shift direction varies with different bands - Up or Down Standards require access by 1750Hz Toneburst or CTCSS CTCSS - Continuous Tone Coded Squelch System Best to set Local Repeaters up in Radio Memories

Repeater Procedures Repeaters are accessed via a 1750 Hz toneburst or a continuous sub-audible tone (CTCSS) CTCSS helps avoid interfering with other repeaters on the same frequency, particularly during lift conditions Repeaters use various tones and idents in Morse. For example ‘K’, dah-dit-dah. This gives the user notification in between overs that the repeater is resetting and not to key up. Can stop timeouts.

Intermodulation Intermodulation Products are often termed IMPs or PIM Need to identify whether a distant transmitter or your own receiver is producing intermod products. Intermodulation is a non-linear mixing effect caused by overloading and is power dependent Intermodulation in a receiver can identified by inserting an attenuator (or turning the beam away) until signal is well below full-scale on the S-meter. If ok then it was the receiver at fault, else the problem is at the transmitter. Note: If the Tx power itself is reduced, the fault will go away regardless of where the problem really lies. Worth remembering for resolving problems, contests etc

Special Event Stations Set up for events of special significance, worthy of celebration and that are open to viewing by the public Two main types of SES both requiring good preparation to be a success: Demonstration Stations and Talk-in Stations Demonstration stations must show the hobby in an interesting, attractive and informative way Talk-in stations need to know the local area, have access to a large scale map, be patient, with prepared directions from all major road junctions Both types of SES station can use the callsign of a full licence holder or they can apply 28 days in advance with an explanation of why the call is required

Special Event Callsigns Both types of SES station can use the callsign of a full licence holder. Alternatively a full licence holder can apply for a GB3, 7or 9 callsign. Applications must be made to the RSGB at least 28 days in advance of the event and must be accompanied by an explanation of why the callsign is required.

Bandplans Bandplans are agreed internationally with the International Amateur Radio Union, IARU Though not legally enforceable, bandplans are essential to avoid interference to other band users Key points: No SSB in the 30m (10MHz) band No contests in the 12m (24MHz), 17m (18MHz) and 30m (10MHz) bands Narrow band modes are at the lower ends of each band Transmitting on Beacon frequencies must be avoided Transmitting on Satellite frequencies should be avoided

Bandplan Example