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The art of Long Distance FM DXing

February 5th, 2008

I will describe my experiences in receiving long distance FM here.

For receiving long distance FM (or FM Dxing) the first thing you need is a good radio. Good receivers are hard to find nowadays. If you can find a Phillips of Sony radio you are half way through. (I think Phillips no longer markets radios in India). There are several cheap Chinese radios available in the market. They are ok for a casual Dxer. Some radios today can automatically scan the FM band for stations. I don’t recommend them.

Next step is to build an antenna. There are several possibilities for this . Some of them are dipole. folded dipole or even a quad.

First let us see how to construct a simple dipole. The FM band is from88MHz to 108Mhz. We will design a dipole tuned at the centre of the FM band.( ie 98Mhz)

The formula for calucualting dipole length is =468/Frequency in Mhz.

I n our case the length works out to be 4.78 feet.

Get hold of 2 pieces of copper wire.( If you cannot find, buy two pieces of 1/2inch aluminum rod or welding rod. As a ham I use welding rods for all my VHF antennas) . Fix them on a PVC pipe ( Use your ingenuity for fixing them. ) the Dipole antenna has an impedance of approximately 75 ohms. You can buy sufficient length of coaxial cable for connecting your dipole to the radio.

Fix the dipole at a good height. Keep it horizontal ( FM uses horizontal polarization ). The other end of the coaxial cable must be connected to the radio. Most of the modern radios use a telescopic areal. Fold it to the minimum position and fix the inner wire of the coaxial cable to th telescopic areal .The outer braid may be connected to the negative terminal of the battery.

Some of the older TVs used to have rabbit ear antenna. ( a small detachable dipole whit adjustable length) If you can locate one , it can be directly used as a dipole.

Your mileage may vary depending on your location,atmospheric conditions etc

I have seen folded dipoles and rectangular loops suitable for FM reception in some of the electronics shops in Trivandrum. They are mainly used here to receive Suriyan FM broadcasting from Tirunelveli. I don’t know whether they are still available.

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