The Emergency Measures Radio Group is building a Packet Radio Network to support emergency communications between key sites such as the City of Ottawa Emergency Operations Centre, Ottawa Red Cross HQ and shelters. The network can be used by all amateurs when there is no emergency, however the network will be optimized for emergency use, not daily amateur use, which means there are no beacons, BBSs or Internet gateways, other than those directly operated by EMRG, so EMRG can turn them off in an emergency.
Packet radio at 1200 baud can be slow and drops to half speed when going through a digipeater. The data rate gets further reduced when there are multiple stations on the air causing data collisions. When setting up the packet network, EMRG looked for a frequency that was not in use, so the network created by EMRG could be dedicated to emergency communications. By operating the network without any stations that are not involved in providing emergency communications, ensures that the only stations that can cause data collisions, are EMRG stations.
| While there are lots of things that can be done with Packet Radio, one critical consideration in all decisions is that EMRG only build what can and will be supported by it's membership. Building capabilities that cannot be used by most members or which cannot be maintained by the group, adds no long term value. |
The EMRG packet network will support Keyboard to Keyboard text messaging and File Transfers between packet stations with operators. There will be no automatic or unattended systems, other than a few beacons and nodes established as part of the network.
Stations can connect to each other and send text, so the message typed on one PC appears on the screen of the other PC. The message can be printed for distribution to the recipient, it can be saved as a text file, or it can be copied into another message or document.
With the current use of computers, much of the information people need to exchange is contained in documents or spreadsheets, which provide formatting for columns and headers or special text. Transferring this information by re-typing it as text is a duplication of effort and the message looses some of its clarity with the loss of formatting. Unfortunately these files cannot be transferred directly over the packet network. There is a solution, if the documents are only a page or 2, they can be added to a zip file, which is a binary file, which can be transferred over packet radio.
There will be NO Bulletin Board Systems (BBS) in the EMRG packet network. The BBS was common in packet radio networks, allowing users to exchange e-mail, gather information and download files. The EMRG network will not support the use of a BBS for three reasons;
EMRG is operating a Telpac, Internet e-mail gateway as a test of the Winlink 2000 network. www.winlink.org
The 1200 baud Terminal Node Controllers (TNC) is the most common TNC owned by Amateurs. For that reason the EMRG packet network must support 1200 baud access. Standard radios will support 1200 baud without modification and EMRG has several 1200 baud TNCs, so this will be the first capability implemented by EMRG.
Multiple users exchanging text or file transfers, will cause congestion of a 1200 Baud network. Implementing a 9600 baud backbone network, with direct access for heavy users such as the Red Cross or EOC, plus gateways to lower speed networks is a capability that could be useful. This would require a solution to support 9600 baud, which means suitable TNCs, plus radios modified to provide connections to support 9600 baud. This may be a longer term project, but is not currently planned for the network.
There are possibilities to support higher speed backbone links, such as 56k or higher using Wireless LAN technology, which can operate in the 2.4 GHz spectrum available to amateur radio and which is unlicensed anyway. While this would be great from a theoretical point of view, it adds complexity and cost that exceeds current capabilities and requirements.
The most common FM radio owned by Amateurs, is 2m VHF, so the network must support VHF radios using 1200 baud as the core connectivity solution. This will be the starting point for the EMRG network design, a single wide area 2 metre VHF 1200 baud network on 145.030 MHz.
The 2 metre amateur band can support additional packet networks and can support 9600 baud communications. The advantage of an all VHF network is the ability to share antennas using suitable coupling devices. The down side is that without the proper coupling devices, multiple VHF stations can interfere with each other if in close proximity and may interfere with voice communications.
The 220 MHz amateur band is an ideal place for packet radio operation, based on the limited use of the frequencies today. The limited use of the band is due to or caused by a lack of available equipment. Some manufacturers do make Amateur equipment, which would work well for an end user station, but finding equipment for central nodes, that can support continuous operation is more difficult.
EMRG will not rule out using the Amateur 220 MHz band for packet, but this will require all new equipment, which may be money better spent in other areas.
The 440 MHz amateur band could be used to support a 9600 baud backbone network. EMRG does not have UHF equipment for this, but there is used commercial equipment available at reasonable cost.
Interfacing the City wide packet network to the long range HF network is a possible future capability, but not a priority until the City wide network is complete and operational, which includes documentation, testing, training and exercises.
Nodes and Digipeaters are similar in terms of the function they provide, but differ in how they provide it. One of the network design objectives is to limit the number of hops to get from one station to another.
There are three key types of network stations required for the EMRG Packet Radio Network;
The radios for the packet stations are Motorola Radius model M120, or GE Phoenix PSX-200. These are 2 channel VHF radios, allowing one channel for 1200 bps and one for 9600 bps. The Radius M120 and GE PSX-200 radios are software programmable so frequency changes can be made if required. Modification information has been obtained for the radios, for supporting 9600 bps operation.
The duty cycle of the radios must be considered to ensure that under load, the radio will not fail. Lower transmit power, improved heat sink capacity and fans for better airflow will be incorporated to ensure continuous system operation. The central site will require a commercial continuous duty transceiver because all stations will be routed through this node, making it active almost continuously.
The fixed sites have commercial VHF antennas or VHF antennas are being installed as part of site changes, such as the Ottawa Red Cross move to a new building. Portable systems will use a mix of home brew 1/4 wave and 5/8 J-Pole antennas as well as a few commercial 210C antennas. There will be a pool of antennas with the antenna selection made based on where the system will be deployed. The antenna for the central node is a Sinclair 210C-4, currently installed on the tower at Randall Dispatch.
Seven sections of RG8x coax, fifty feet long, with PL259 connectors on each end, are required for the portable kits. The coax provides the connection from the radio to the antenna. The coax and connectors will need to be purchased.
The fixed sites have a mix of computers, from Pentium 133 MHz up. The computer does not need to be state of the art to run the windows packet program. The portable systems are made up of laptop computers donated by a local company. The systems are in excellent shape and will provide plenty of performance.
There are several software applications for packet radio. Many were written many years ago for DOS, but there are a few written for windows. The windows based packet software will be used because it allows cut and paste of text information from other applications, support for APRS and the ability to use other windows based applications.
There are several options, including Sound Card Interfaces and TNCs. The decision on which to use, depending on functionality and available resources. Equipment must be purchased so money must be found to support the purchases. Sound card interfaces will not work with all computers or software and seem to provide less reliability with weaker signals. EMRG will not pursue the use of sound cards unless than can be proven effective for the EMRG applications.