Antenna Suggestions

Description

When dealing with local organizations such as hospitals, fire departments or municipal emergency planners, regarding permanent radio installations, there is always the question of what is required and how much will it cost. For example a local fire department wants to have a permanent amateur radio installation at a fire station.

There are several options, depending on just how prepared an organization wants to be. Typically the goal is to find an antenna that is simple, long lasting and economical.

Some of the questions are:

  1. What is a good all purpose antenna for installation at a site such as an EOC or fire station?
  2. Should it be a dual band or single band antenna?
  3. Who should do the installation?
  4. Is height a good thing or a bad thing?

By far, the most popular antenna for a permanent emergency installation, is the Sinclair 210-C. This is a very durable single loop VHF antenna which covers 138 to 174 Mhz. There are other antennas in this family, the 210-C2 and 210-C4 are popular for commercial and repeater use. The wide bandwidth capability, makes the antenna very appealing, because it can be used for commercial and amateur frequencies.

Dual band antennas are great for installations where operating two radios on different nets is a requirement. In Ottawa, there are several Diamond 200A dual band and 3200A tri-band base antennas which have been installed for over 10 years and they are still working well. Some people have reported problems with dual band antennas failing early in there life, due to the design and the affects of wind loading.

When it comes to installation of the antennas there are three choices:

  1. Have the installation done by professionals. This will cost more money for the agency paying for the antenna, but it resolves the issues of liability. In many cases, the group paying for the radio already has a commercial radio shop who does work on their existing antennas. The problem with commercial companies, is that they don't always do a good job and corrective action is often required later.
  2. Have the installation done by professionals, but ensure that your radio group has someone knowledgeable involved to oversee the installation. This helps to point out problems during the installation when then can be corrected more easily.
  3. Have the local radio group install the antenna. Based on past history and relationships, this may be an acceptable solution. Beware that there are liability issues, during the installation (what if you put a hole in the roof) and once the antenna is installed (what is lightning starts a fire).

Antenna location is an important issue. Having the highest antenna may not be a great idea, unless you have a radio with great intermod rejection capability. The purpose of the antenna will help decide how high it needs to be. Local repeater use may succeed well, with a simple antenna at roof level.

Simple and Cheap Pocket Quarter Wave Antenna

The following link shows a simple quarter wave antenna made using an inverted SO239 chassis connector. This is a common antenna shown in many antenna books. The antenna can be used for 146, 225 or 445 MHz.

http://www.caryncrepeater.com/images/WX_Radio_Antenna1.jpg

Use #12 electrical wire for the radials and the vertical portion. This wire can be purchased by the metre (foot) at hardware stores as 2/12 house wire, you will need 2M ( 4 to 6 feet). Remove the outer insulation so you have a white wire, black wire and the ground.

Build the antenna as shown, cutting it for the 146 Mhz lengths. You can make the antenna with three wires for radials and 1 for the vertical, or you can use all 4 holes in the SO239 connector and make 4 radials if you want.

Use a round form such as a piece of pipe about 3/4 to 1" diameter and roll up each of the wires, starting at the outer end of each wire, rolling it into the centre. When you are done, the antenna looks like a bunch of coils attached to the connector. While you need big pockets to store this in, it doesn't take up much space and is ready to be straightened out in an emergency. Keep the 225 and 445 lengths with the antenna, so you can always cut it in the field if required for a different band.

For mounting the antenna, use a short length of 3/4 PVC (white) plumbing pipe. If you cut a 10 cm (4 to 6") slot in the end of the pipe, a PL259 will slide in and the cable will exit through the slot. Just attach the cable to the antenna, slide the PL259 into the pipe and then attach the pipe to something.

You can enhance this antenna with a simple extension mast, coloured wire etc.

(I'll try to add a picture in the future)