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 Previous: Surfin': Put Up To Stay Up | ![Next (later) Story](/images/sty-up.gif "FEMA to FCC: BPL will "Severely Impair" Mission-Essential HF Operations"){kind=small} Next: FEMA to FCC: BPL will "Severely Impair" Mission-Essential HF Operations |
By John A. Allocca, WB2LUA
December 7, 2003
That 5 W handheld transceiver not cutting it when you do volunteer public service work? Consider building a portable station that packs a punch, in both all-in-one and modular models.
 Allocca's full-featured station is capable of operating FM, packet and APRS on 2 meters and 70 cm from both ac mains and 12 V gel cell battery. [Photo, John Allocca, WB2LUA] |
Recently, I had to cover a local running race. We needed an operator at each mile marker, at the EMS dispatch center and various other locations. I served as the net control station and encountered two major problems. First, a crowd of about 200 cheering and screaming people surrounded me. Additionally, the race organizers had a loud PA system going and a helicopter made numerous passes overhead. I had a great deal of difficulty hearing the radio, even with an earbud. The second problem I had was being located in the middle of tall buildings with a 5 W handheld transceiver. My power was low and it was often difficult to hear others with their 5 W handheld transceivers.
Although this was a non-emergency event, it was a viable scenario for an emergency event. These problems needed to be solved for future events and for emergencies. I defined a set of requirements I felt would overcome the problems I encountered:
 All shelves slide in and out for easy access to components. The top shelf contains the notebook computer; the second shelf contains the radio, speaker, antenna tuner and external speaker; the third shelf contains the switchbox, power supply and inverter, and the fourth shelf contains a clipboard and manuals. The battery and charger are stowed in the compartment at the bottom, and the station is mounted on a wheeled, steel cart. [Photo, John Allocca, WB2LUA] |
 In the second incarnation of the station, the modular design allows the operator to take only those parts of the station that are necessary to the task at hand. The three levels of the box, held together by clasps on the sides, can be separated for easy transportation and greatly reduced weight. For example, the heavier battery box can be left out if ac power will be available. The radios are mounted on a pullout board, and the dedicated laptop has been removed. [Photo, John Allocca, WB2LUA] |
I decided to build my own portable station that would meet all these needs. It can be used for emergencies and non-emergency community service. I felt it was important to integrate packet because it is often used when there are a lot of details to be transmitted, such as a request for hospital supplies. APRS, a mode we are beginning to experiment with, can be valuable when one needs to know where operators are if they are given a field assignment during a disaster. The enclosure and its hardware cost about $75; from there, price is determined by how you stock the station.
I chose a Kenwood TM-D700A, a dual-band mobile radio capable of 5, 10 and 50 W. The radio has a built-in TNC for packet and APRS, and it ties in to a notebook computer for sending and receiving packet and to view APRS locations on a map.
When it came to the antenna, I had a lot decisions to make. Taller is better, but then again, taller is less portable. I finally decided on the Diamond X50A base station antenna, which is about 5.5 feet tall and uses a 1.25-inch diameter, 6-foot aluminum tube for the mast. The mast slides into a PCV pipe mounted on the side of the station. All of this breaks down to fit into a car. I replaced the U bolts on the antenna with 1/4-20, 2.5-inch bolts and wing nuts so that it's fast and easy to assemble and disassemble. The station weighs 116 pounds; two people can easily lift it in and out of a car by the four handles on the case. Once out of the car, it can be easily moved on its large wheels.
The station can be operated from 120 V ac, running to a 12 V, 23 A switching ac power supply. Power can also be drawn from a 31 A/h gel cell battery and 120 V ac inverter. A battery charger is also located in the battery compartment. I built a switchbox so that I can turn the charger on and off, turn the inverter on and off and switch from battery to ac. I also included an MFJ 2 meter/70 cm antenna tuner to obtain the best match with the X50A. A Garmin Emap GPS receiver rounds out the equipment.
All of the shelves slide in and out for easy access to components. The computer shelf had to be a double sliding shelf so that the computer can be opened. To solve the problem of noise, I selected the Heil Pro-Set headset with microphone. It works quite well at reducing background noise.
The original Emergency Communications Portable Base Station had several advantages and several disadvantages. It had the advantage of everything being contained in a single package; the disadvantage is that it required two people to transport and larger vehicle to haul it. Enter "Emergency Communications Portable Base Station II," which can be transported by a single person. Clasps hold the various modules together, once a position of operation has been established. The modular design allows for only transporting the needed equipment for a particular event. For example, if ac power is available, the battery module will not be required, and so on.
That's it, and it certainly provides more punch than a single FM handheld, making the station--all-in-one or modular design--perfect for all kinds of volunteer service work.
John A. Allocca, WB2LUA, is a medical research scientist whose company is called Allocca Technology and Healthcare Research. He lives in Northport, New York and can be reached via e-mail.
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