Dr. John Champa/K8OCL
Emergency communications offer the greatest opportunity for Radio Local Area Network (RLAN) technology to excel and for amateurs to push the envelope in the public service sector, using this technology. Low power requirements, low cost, portability, point- to-point, point-to-multipoint and multicast capabilities, coupled with high bandwidth, make RLANs an excellent technology for "on- the-spot" emergency communications.
An emergency volunteer radio operator can be equipped with a laptop or a wireless PDA (Personal Digital Assistant) with a microphone and a small video camera or used as a "record" message interface. They now have the tools needed to act as a mobile set of eyes and ears in the midst of a communications emergency.
Since the 9/11 tragedy, Amateur Radio has taken on a heightened role in national, regional and local area emergency communications. Emergency communication organizations such as RACES and ARES are establishing emergency response plans with local and state government organizations as well as with many disaster relief organizations. The ARRL is in contact with organizations and federal agencies such as the National Communication System (NCS), Federal Emergency Management Agency (FEMA), American Red Cross, and Salvation Army. The National Weather Service "SkyWarn" effort works with local amateur radio groups to provide vital severe weather data within specific communities and area.
Along with traditional communication channels, such as HF, V/UHF, packet radio and APRS radio communications, wireless networks need to become an integral part of the Amateur Radio communications response capability.
Hardly a month goes by without reading about how amateur radio operators assist during natural disasters.tornados, hurricanes, snow and ice storms, earthquakes and forest fires all stress to the limit normal communications and in many cases render those normal communications useless.
For the over 90 years, amateur radio operators have stepped up to the challenge of replacing or augmenting lost or over burdened communications with our ham radio capability. As we enter this new century, we find that the communications we have been accustomed to providing in the past, while appreciated by those we server, appear to not fully meet their disaster communications needs.
To partially fill that gap, we can deploy IEEE 802.11b and 802.11g networks operating under Part 97 of the FCC rules. 802.11b/g offers several unique network and communications options that amateurs have for the most part never used before.
Here is a list of communications equipment needed to provide this new method of amateur radio communications using the IEEE 802.11b/g standard and operating under Part 97.
To operate two "nodes" in a point-to-point operations, you will need the following equipment:.
1) A RLAN card for a PC or Laptop or an external network device (END) such as the LinkSys WET11. Cost ~$100
2) A directional high gain antenna such as a 20 dBi gain parabolic antenna. Cost ~$75
3) Misc. coax, RLAN device coax pigtails and CAT 5 cable. Cost ~$100.
4) Optionally you should consider purchasing a bi- directional amplifier (BDA). The cost of an 800mw BDA from RF Linx is ~$120. Other cost associated with a node is a mast, mount and other antenna hardware. You may already have some of the equipment in your ham shack or in your computer room.
The above network equipment will work with any computer having a network interface card (NIC) or if a RLAN card is used, a PCI slot or PCMCIA slot.
Two similar nodes are of course required for point-to-point operation and will normally work in the ad-hoc mode.
The equipment described above for point-to-point operation can be used for the nodes in an Ad-hoc network except the directional antenna must be replaced with omni-directional antenna or wide beam width antennas such as 120 or 180 degree panel arrays. While horizontal polarization is desired, the lack of inexpensive commercial horizontally polarized omni-directional antennas may require the use of vertically polarized antennas. A good omni- directional vertically polarized antenna will cost about the same as a parabolic antenna. Use of an omni-directional antenna helps minimize the "hidden transmitter" effect.
The same basic node equipment is used for the nodes in an Infrastructure network as in an Ad-hoc network. The only difference is in the access point (AP) you must substitute the END with an AP. Common APs such as the LinkSys WAP11, cost anywhere from $90 to $150.
The hidden transmitter effect is also present in the infrastructure net since in this instance several member/client nodes will not be in line-of-sight (LOS) with each other. Commonly, an AP is located geographically like a repeater is.high enough to be LOS with all the network client nodes.