2006-11-11
FM Broadcast Receive Antenna
I use a WinRadio WR-1550e on the shack computer for casual listening and scanning, and it needs a pretty good antenna. I threw this antenna together for FM broadcast listening with this radio, but it is a general purpose antenna for 3 metres that can be scaled to any VHF or UHF frequency.
It is made completely from 300 Ohm TV ribbon transmission line, simply cut to the right length, then shorted at each end and fed on one side in the middle.
As the radio has a low input impedance (50 Ohms nominally) I built a quick 4:1 balun to match the 300 Ohm balanced feeder into the lower impedance (ignoring the minor 75:50 Ohm mismatch). A commercial ADT1-1 minicircuits transformer was used, but you could just as easily use a ferrite bead to wind your own or buy a commercial TV balun which is essentially identical internally, but terminates in those terrible TV plugs rather than a BNC. The ADT1-1 was small enough to slip down inside the BNC plug, so I simply potted it in epoxy inside the plug and put some heat-shrink over the works to hold the TV ribbon in place.
The antenna works fine and has plenty of bandwidth for the FM broadcast band. It was actually cut for the harmonic mean of 88-108 MHz (96.980 MHz, 3.091 metres) and resonated carefully with a VHF dipper, but this is complete overkill, an untrimmed 1.5 metres of twinlead will work just as well.
I simply tape mine to the wall of the shack, you can string yours up however you like, or make it positionable, etc.
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Attachments
| title | type | size |
|---|---|---|
| Antenna Diagram Source | application/postscript | 12.060 kbytes |