[TowerTalk] Field Day Interference

Dennis W0JX w0jx at yahoo.com
Thu Jul 3 19:52:15 EDT 2008

Thanks to Frank, W3LPL, for the great ideas to minimize interstation interference on Field Day. Our station, NI8G, worked W3AO on at least 2 bands.
We did not have the luxury of the large circle. Our three antennas consisted of an 80 meter dipole fed with open wire, a 40 meter dipole, a twenty meter ground plane, and a six meter beam. The antennas were within a 200 foot circle. Our 80 and 40 meter dipoles met his "end to end" criteria.
We minimized interference on 40 and 20 with coaxial stubs. Second harmonic interference was minimized by using a 20 meter,1/4 wave line section at the output of the 40 meter station, followed with a shorted, 40 meter quarter-wave stub connected at the input of a Drake MN-2000 tuner. At the output of the 20 meter station, an open, quarter-wave 40 meter stub was used to reduce fundamental overload energy. We had no noticeable interference between these stations, nor did the 80 meter CW station bother the 40 meter station. A Johnson, 275 watt Matchbox was used on 80 CW, plus the other bands as needed.
We did have a problem when the 20 meter station was operating BPSK. Its second harmonic created significant interference on 10 CW but we just asked the BPSK op to stop Cqing when we needed to finish a Q.
The biggest surprise was how well the center fed, 80 meter dipole worked, especially on 10 and 15 meters. It was up high, almost 60 feet at one end sloping down to about 40 feet at the other. If we could have only one antenna on Field Day, the open wire fed, 135 foot dipole would be it.
73, Dennis W0JX/NI8G 


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