Just thought I'd throw this out there to see if anybody had any
ideas... I was recently playing with an 800 to 1000 MHz Log design. It
came out quite well in the model. It was showing that it should do
about 1 to 1.5 average SWR, with a couple little spikes of 2.0 or so.
So I went ahead and built it.

Now I know from past experience, that testing logs is very tricky.
Unless you have a phase stable cable right up to the feed point, you
can get all kinds of crazy readings. But still, you can usually get
the gist of what's going on. So I go to test the actual finished
antenna, and across the intended range, it's showing SWR as high as 7
or 8, and the best it goes down to is maybe 3. Totally different than
the model. As a test, I went to the NEC model and took off all the UHF
elements, and just added one VHF element to the low end... It showed
around 155 MHz in the model. I did the same thing on the actual
antenna and got 1.1 around 153 MHz. So at that range, it's right on.
But I am baffled as to why it is so terrible on the UHF. I tried
shorting the back end and not shorting. No real difference.

Any ideas?

Thanks,