MakeGizmos homemade devices pg 8

Slickditty MakeGizmos

Make-it-yourself devices archive page 8

weather radio antenna:

My home is about 25 miles away from the nearest National Oceanic and Atmospheric Administration Weather Radio All Hazards program transmitter. The station broadcasts weather reports and forecasts and emergency messages about any hazardous situations. My weather radio receives their broadcasts loud and clear most of the time. But when it's raining sometimes the signal fades away because the rain absorbs some of the signal. I had been using the radio's built in telescoping rod antenna. It seemed to me, it would be prudent to have more reliable reception of those signals. So to get a stronger signal and better reception, I made a high gain antenna and put it in my attic.

I got online, found a design for an antenna, looked around the premises for the materials, thought of how to implement fabrication, built the design diagramed below, installed the antenna in my attic, and now have more reliable reception. I don't use the radio much. I usually get weather forecasts online were they are accessable quicker than listening to a repeating loop of messages on the radio until the forecast is given. But the radio is there if needed in an emergency. It has battery backup if the power grid goes down.

To make the antenna I drilled 1/8 inch diameter holes in a 1 1/2 inch by 1 1/2 inch by 5 foot piece of wood. A single straight piece of wire goes through each of those holes. See the diagrams below. I used wire from clotheshangers. One hole is drilled for each of four of the five wire elements. The fifth element (shown in red) actually is made of two pieces of wire. That two-piece element is called the driven element and is where the antenna signal is developed. It's probably easiest to drill two holes for that fifth element (more about that later). I made my antenna with just one hole, drove a 3/8 inch long piece of cylindrical plastic into the hole, inserted one wire into either end of the hole, pushed in 3/8 inch long pieces of wire as shims to wedge the long wires securely in place. The plastic spacer keeps the two long wires separated. The second diagram below shows the connection of the RG59 coax that carries the signal to the weather radio. I sand papered a 1/4 inch or so wide area of wire next to the wooden boom, then soldered the braided copper coax shield to one driven element and soldered the coax center conductor to the other driven element piece.

I hung the antenna using string tied to nails driven into roof rafters in my attic. The antenna is almost directly above the wall on which the radio is mounted. About 5 feet of coax carries the signal from the antenna to the radio.

If I make another such antenna, I would use two holes for the driven element. The two holes could be, say 1/4 inch on either side of the design position of the driven element. I suppose being off by 1/4 inch would have no significant effect on the antenna's performance. Using a single hole allows each wire to be inserted for something under half as far into the wood boom. So the shim method probably isn't as secure as how I secured the other elements. To secure them I ran a doubled length of rubber band through the hole, stretch the rubber band tight to reduce its thickness, inserted the wire and released the tension on the rubberband. To get the rubber band through the hole, a loop of thin, stiff plastic cord can be pushed through the hole, the rubber band inserted in the loop, and the loop pulled back out of the hole, pulling the rubber band with it.

I used a five element antenna (this design is called a Yagi antenna). A yagi can be made with two or more elements. The more elements, the stronger the signal and the greater the antenna's ability to pick up the signal toward which it is aimed and reject interferring signals from other directions. It seems that a 3 element yagi is perhaps a good compromise between performance and ease of construction. You can go online and get specifications for the length of the elements and their spacing. The Weather Radio All Hazards broadcast are all very close to 162MHz in frequency. Here are some web sites you can use to get the specs.

www.csgnetwork.com/antennae7ycalc.html (7 element yagi) www.csgnetwork.com/antennae3ycalc.html (3 element yagi) www.csgnetwork.com/antennaegpcalc.html (1/4 wave vertical with 4 horizontal ground plane elements) www.od5sk.com/guide-javacalculator.htm bfn.org/~bn589/antenna.html (3 element yagi)

If you live closer than 20 miles of a transmitter, you won't need such an antenna (unless you also want to pick up a more distant station). I'm guessing that if you live farther than about 40 miles you probably won't get acceptable reception even with the antenna. The distances are somewhat affected by whether you are at a high elevation up above any obstructions to the signal or down in a valley shadowed by hills and such. If you want to try this, try to get a radio with a jack for an external antenna. I have a radio with a built in jack in my car. It might also be possible to modify a radio that has no built in jack but does have a telescoping rod antenna. That's what I did for the weather radio I use in my home. I mounted a jack for the RG59 cable on an angle bracket that I bolted to the outside of the radio. I opened the radio case, unsoldered the lead going to the rod antenna, and soldered the lead to the center connector of the RG59 connector. There's a picture somewhere here of that radio.

One note about weather radios. The two radios I have are older radios without a feature called SAME. The SAME technology allows you to program the radio so that the radio will turn itself on if a warning or emergency message is being broadcast for the area in which you live. My older radios switch on if a message is being broadcast for any area within the transmitter's range. If I leave my radios on during thunderstorm season, they switch on so often that it becomes a nuisance. So I usually leave the radios turned off. I suppose with SAME technology there would not be such a problem.

The narrow lines are wire, the wide section is the wooden boom that holds the wire. The red line is the wire from which the signal is taken by a cable that runs to the radio. The connection of that cable is shown in the second diagram. The distances in inches from left to to right, measured from the first element, are 0, 12 1/4, 17 5/8, 27 1/2, and 41 9/16. The lengths of the elements are 1) 40 7/8, 2) 37 5/8, 3) 37 5/8, 4) 36 11/16, and 5) 36.

The RG59 cable's braided copper jacket is bundled, wrapped around one clotheshanger wire, and soldered. The cable's center conductor is soldered to the other driven element wire.