UWE wrote:
"I would like to put up a big hi gain FM broadcast band antenna."

1.5 wavelengths is about 15 feet near the center of the FM broadcast
band. Kraus gives an example of this 6-element Yagi. It has a radiator,
reflector, and 4 directors in Fig. 8-29 on page 248 of his 3rd edition
of "Antennas". Directivity is about 12 dBi and bandwidth is 10%.
Construction is not too critical because the space between its elements
is fairly wide.

I have built Yagis and been pleased with their performance.

Best regards, Richard Harrison, KB5WZI