Choosing the correct toroid size is actually a compromise larger cores can handle higher power, but since the inductance per turn is higher, it is more difficult to wind a large toroid to an exact inductance. A common error when making toroid wound inductors is selecting toroids that are too small to handle the required power. Unfortunately, I made a poor decision when choosing components to build the filter. To avoid damage to any of the radios, a filter designed for 6 meters that will reject signals from 10 meters is needed.
While that filter will help avoid the transmission of harmonics at 56 MHz (28 * 2), the radio being used on 6 meters will likely get overloaded or could even burn up from the excessive signal on 10 meters. The 10 meter station will be using a band-pass filter which should reduce the second harmonic, which happens to fall near 6 meters. Due to physical constraints on where antennas can be erected at the American Legion, the antennas for HF and 6 meters will likely be too close to avoid inter-station interference just by distancing the antennas. The VHF station captain (myself) decided for sake of simplicity to not attempt to use a 6 meter beam, but rather just a simple dipole on a 30 foot fiberglass pushup mast. While we could add additional multiplexers in hopes of using 6 meters on the TFD, the complexity of the system is unreasonable, and even then, the performance of the TFD on 6 meters is sub optimal. As mentioned in the earlier post describing the TFD (Terminated Folded Dipole), we plan to use a single antenna with a number of filters on each of the HF radios. While we have traditionally stayed on the HF bands at our Field Days, there is activity that occurs up on 6 meters that we hope to be able to take advantage of this year. This year, SARA plans to include a VHF station in our yearly Field Day setup.