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Monday, August 1, 2011

Amateur Radio Directed net

A net or directed net, in radio-amateur operating procedure, is an organised meeting of multiple stations on a common frequency at a scheduled time. One station is designated to serve as net control; all requests to deliver message traffic to the net are initiated by sending an identifier or callsign to the control station and waiting for that station to reply before continuing.

The directed net structure reduces the number of message collisions, where multiple stations attempting to transmit simultaneously could otherwise cause unwanted interference to communication within the group.

Directed nets are commonly used for scheduled on-air meetings of individual radio-amateur groups. They are also activated to co-ordinate disaster and emergency communication between volunteers during local events and to co-ordinate data collection and weather spotting activity during a regional storm watch or warning.

A scheduled net will often use a pre-defined script which identifies the purpose of the net, invites stations to "check in", allocates time for individual stations to send their traffic sequentially, delivers any announcements and then ends the directed net once all traffic is completed.

This script, as an example, is based on a weekly on-air meeting of a local radio-amateur group. While elements of the basic structure are similar between different nets, individual organisations can and do adapt the general structure to suit their needs.

This is (name)_________ , (call sign)___________, Net Control Operator for the ______ Net.
This net meets at (time)_________ on (frequency)_____________ for the purpose of __________________.

This net is open to anyone interested in (purpose)_____________ in (region served)______________.

If at any time during the Net, should an emergency arise, please notify Net Control. We will stand
by and allow those in need access to this frequency.

Is there any priority or emergency traffic at this time?

This enquiry is **fingers always crossed** greeted with utter silence. So far, so good. Having received no emergency traffic, the net control operator is then free to ask for stations which have routine traffic to identify themselves.

Are there any portable or mobile stations wishing to check in at this time?

Are there any homebase/fixed stations wishing to check in at this time?

Individual stations seeking to address the net send their callsigns, usually in groups of no more than two or three. The net co-ordinator acknowledges each station by callsign, then invites the first station to send its traffic. Once all identified stations in turn have sent any messages, the control operator will ask for the next series of check-in requests.

If traffic is received from a station which is not audible to everyone on the net, but which is receivable at the net control station, the net co-ordinator may repeat the message manually or ask to verify that the intended recipient station copied the traffic. This is not commonly an issue on nets conducted using a local VHF/UHF repeater, but will arise on HF or other simplex nets.

Once all stations in a group (such as mobiles) have finished, the next group is invited to check in to the net. Once all stations wishing to send traffic have done so, time may be allocated for announcements or other specific items before ending the directed net.

Do we have any stations with announcements, bulletins, or news of general interest to the net?

Last call for any stations wishing to check-in to the __________ net,
or any further comments or questions.

There being no further check-ins or comments, this is (call sign)__________
closing the _________ Net, Thanks to all for participating.

This frequency is now returned to regular amateur use. 73 to all.

Stations deployed to provide communication service during public events, or as part of emergency communications operation, will often bear an additional identifier meaningful within the individual net. While these do not fully replace the station's globally-unique government-issued callsigns, they are employed to address traffic within an net based on the rôle a station at a specific location plays in the larger operation. Each deployed ARES or emergency service net at an event will typically contain one control, various fixed stations designated by place name (a town or location) and/or individual mobile units labelled by purpose (admin-one, repair 2...) depending on the incident and the needed response.

While there is normally only one control node on-frequency in the same net at any time, procedure should provide for another station to seamlessly take over the control-one identity and position if the existing control-one station loses backup power or has to abruptly leave the air for any reason. The use of tactical calls ensures that inbound enquiries to the net can continue to be addressed to control without regard for which individual licensed station on the net is currently occupying the rôle.

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