Sorry about my late entry.. just joined. The ripples on the original 70cm VSWR image are the sort of thing regularly seen in microwave waveguide return loss measurements. These RL/VSWR ripples indicate an impedance mismatch or bump which (as suggested) a TDR can find. The other really interesting behavior which we used in the waveguide world, was the 'frequency difference' of one cycle of that sinusoidal pattern.. in your case I counted 3.5 cycles over the (453.9-436.5Mhz interval), giving 4.971Mhz per cycle (a 60.3m wavelength). With a half wavelength of 30.2m, that would be the free space distance to the mismatch bump point.. However, in coax with say a 0.66 VF (like LMR400), the real distance would be about 19.9m.. which I'd have it a guess is about the length of your coax..
If possible, try and substitute a different length coax, and repeat the measurement.. Just an idea...
David Burger
Chartered PE, Sydney.
