Larry Gadallah
Larry Gadallah


I had a great, but minimalist Field Day this year, where I finally got to transmit on my Icom IC-705, operated on 6 meters for the first time, and experienced QRP operation for the first time.

As part of this effort, of course I put up an HF antenna for use on Field Day; an 80M/40M fan dipole.

My friend Mike, KG7HQ, hooked up his portable antenna analyzer to it and found it looked okay for 80M, but was way off-frequency for 40M. It was showing a VSWR dip closer to 6.6 MHz rather than the 7.2 MHz expected for 40M operation.

I finally got a few minutes to get my PocketVNA VNA running and calibrated, and I took a closer look:

80-40M Fan Dipole Too Long

80-40M Fan Dipole With 40M Too Long

As can be seen from the above, the 40M portion of the fan dipole definitely appears to be a bit too long. Doing some rudumentary calculations using the classic dipole length formula (468 divided by frequency), I determined that the 40M dipole was about 2 feet, 9 inches too long.

So today, I went out into the rain, lowered the 40M dipole legs and shortened them by about 2 feet, 6 inches. Running another scan on the VNA, I can see that the 40M dipole now resonates within the 40M band, albeit still a little low:

80-40M Fan Dipole Better

80-40M Fan Dipole Closer to Being Tuned

It’s always comforting and reassuring when there is some evidence that theory and practice sometimes match, especially when it comes to antennas and RF.