EOC Antenna Layout

2m and 70cm / VHF and UHF

EOC's (Emergency Operations Centres) are not at all like the average ham shack. They don't depend on one person using a radio at a time as you may have going on at home. They may have three or 4 people talking simultaneously in the same room. It's tough enough trying to talk over the background chatter but it's a lot worse when that same background chatter appears on your speaker or earphones. All of the EOC facilities I have attended have that very same thing happening. What we usually have are several 2m radios coupled with coax to several 2m antennas. More often than not the antennas are spread  horizontally around a tower or a roof. The same thing occurs on the roof of an EOC Command Van or Trailer. When you have vertically polarized antennas side by side they cannot hope to do anything else but couple to each other. When one person keys up their microphone someone else wil often be hit by a squawk in their ears via speaker or headphones.

There  are two solutions to this. If you have a tall tower simply spread out the installation of the antennas on the tower vertically. Leave 10 feet or so between them. You put the antenna on the top that needs the most range and the next one down needing less range, etc.   This is not rocket science when you give it thought. A vertical antenna radiates perpendicular (horizontally). Dipole antennas have null points off their ends and so coupling off the ends is minimal.

The second solution is to spread the communications needs over multiple bands. We do have 2m, 6m, 70cm, and the 220 MHz bands to draw upon. Generally speaking you don't usually get cross talk between antennas and radios on different bands. I was looking at a tower at an EOC a short time ago and it had at least 6 each 2m radios with 6 separate antennas on the same tower all in pairs down the tower, a sure recipe for having intermod. and they lived up to it. If half of those radios and antennas could be changed over to 70cm paired with 2m and 70cm at each level on the tower most of their problems would probably go away. Of course the 2m antennas would need to be laid out one above the other and the same for the 70cm antennas.

HF (High Frequency Radios and Antennas)

 The needs of municipal EOC's in the province I am in is quite simple when it comes to HF. EOC's need to be able to communicate with their PEP headquarters either in Greater Victoria or in Kamloops. The distance is too short to go to a DX type antenna that uses something like the 20m band to bounce signals off of the ionosphere. The problem with that is that anything from Victoria to Kamloops is in the skip Zone, the signal goes right over our heads. The only HF left open to us is via ground wave or NVIS (Near Vertical Incidence Sky Wave). A simple inverted V antenna cut for the required frequency is the simplest, cheapest, and best solution. By cutting an inverted V to the resonant length a matching unit or ATU (automatic tuning unit) is redundant, at least for communications of an emergency nature.  It was suggested to me by a friend,  VE7ED, that I put up a pipe cross bar on the local EOC tower, hand pulleys on both ends and 1:1 baluns, and make 40m and 80 meter antennas tuned to voice for one pair and PACTOR on the other pair. It really is a simple setup.Note that the 40m and 80 meter antennas are tied to the same baluns.

 So, no gigantic beam antenna required with large expensive rotor and control.  They are great for making world wide contacts but that is not what a municipal EOC is all about.

The antenna I have at my home is an 80m horizontal loop antenna that stretches around the sides of my yard and is supported by 40 feet of surplus aluminum irrigation pipe at the corners. These are braced by fastening to a variety of things, buildings, fences, trees, etc. So far so good. These pieces of pipe bend in the wind like fishing poles. They are low enough that most of the signal from the loop goes skyward so it is a reasonably effective NVIS (Near Vertical Incidance Skywave) antenna. I can work nets in a 300 mile or more radius. Ones that are only about 100 miles away are very good most of the time but at 300 miles the signal is getting a bit dodgey. Storms passing through exhibiting electrical activity make enough noise to block communication those days.

 The frequencies shown on the diagram are for illustration only. They are specific to the province of British Columbia, Canada. Other groups or provincial emergency programs would have frequencies slected for their own needs.