Is there an advantage to using the Larsen NMO-50 over the NMO-150 for 6m?
And I think the fact that the NMO150 happens to work on 6m is because the coil (VHF matching section) isn't DC grounded. I've come across other VHF 5/8 wave antennas where this isn't the case.
I believe you are thinking of 1/4 wave antennas for VHF being 3/4 wave on UHF. That works well.2 meter and 70 CM are fine with VHF antennas because the are near a perfect 3:1 frequency.
6 meter doesn't multiply evenly so you get bad performance on 6 with any 2 meter antenna.
Likewise, an antenna tuned for 6 works poor on 2 and 70cm.
seeing is believing looking at a VNA.
I will put up screenshots when I get my puter talking to the VNA again.