FM Transmitter Antenna

1/4 Wave FM Transmitt Antenna for 87-108mhz 0.5w-100w


Maximum Power: 100W
Minimum Power: 1mW
Frequency: 88.1-108MHz
Center frequency: 87MHz 92 MHz 98 MHz 103 MHz 108 MHz

Gain: 3db
Impedance: 50 ohms
Bandwidth: VSWR 1.5 or less than 5MHz
Center SWR: < 1.1
Vertical Radiation Angle: 45 degrees

2022-07-05 I recently purchased this antenna for a project for a community radio station and it had a few problems with it as I see things. The tube or shroud that fits at the bottom of the antenna used a screw made from that soft yellow metal which is brittle and breaks and the head often becomes stripped if you need to remove it later. It was easy to find a good stainless steel screw to replace that. In addition the supplied screw was too long which allowed the antenna to rattle. This true is where you will mount the antenna using antenna clamps so if you used the supplied cheap screw someday soon the antenna will fall right off the mounting tube. Needless to say in wind, everything would end up damaged.


Another issue is that the bottom of the mounting tube where the coax cable would exit was sharp. If the cable is flopping around in the wind the cable leading down to your transmitter will eventually be cit and abraded so much that you might ruin the cable. I devised a small widget which you can glue around the cable (do NOT glue this to the inside of the mounting tube!) It is a 2-piece cylinder with a hole in the center which holds the coax cable right at the point where the cable exits the mounting tube. Using this, you can still remove the mounting tube normally and although this widget is glued to the coax you can still replace the cable or disassemble the antenna normally. This "plug" prevents the cable from touching the sharp edges of the mounting tube and helps keep the cable from moving in the wind.


Although my quota problems here at my hosted site are not resolved I hope to upload a few small images and the STL file so that you can print this as well. No copyrights and all are welcome to the design. This was an unexpected update as my eyesight is so bad it is hard to create all this text but I thought it might be work uploading the design and offer it to others whi own this antenna.

The idea is to glue it onto the coax cable right at the end of the mounting tube so it stabilizes the cable and keeps the cable from being damaged from the sharp edges on the mounting tube. It should help keep the cable from moving around as well.

Here you can see the plug installed. I accidentally glued a piece of masking tape but that isn't coming off any time soon.


FM-Transmitter-Antenna-Plug.stl (right click and save)