On 1/21/2013 4:32 PM, Richard Ferryman wrote:
In UK we have 430MHz to 440MHz. I checked the 'SWR' by measuring return
loss at 1MHz steps from 420MHz to 450MHz.. The radiation pattern was
measured outdoors above a snow covered field (the nearest thing I have to
laboratory conditions!) at 435MHz and polar plot made automatically. I
also ran the test with two ferrite blocks on the cable next to the antenna
connector. These were of unknown type but supposed to be similar to type
67. The blocks eliminated the skew with no measurable change in return
loss. The initial skew was really quite small compared with the 3dB
beamwidth but was recognisable on the plot, particularly on the sharper rear
lobes. Curiously there is no skew shown on the plot in the manufacturers
datasheet 220909e.pdf but their photo does show a black 'lump' just to the
rear of the connector. Perhaps they did have a ferrite on there after all!
Dick G4BBH

What did you use to do the plot? I notice you said "automatically". I
saw some software around a few years ago but haven't looked lately. We
do fairly decent gain measurements at NLRS Aurora (nlrs.org) and Central
States, but it's far far from automatic and not also the pattern.

tom
K0TAR