Jim Weir (RST Engineering) has written several articles on this. The
basic rule is to keep any piece of metal (e.g. wire) 1/2 wavelength or
more in dimension, at least 1/4 wavelength (c. 22" here) from the
tips(s) of the antenna. The coax to a dipole should run 90-degrees to
it for at least 1/4 wavelength before any turn. At least radiating
pattern is affected, probably VSWR too.
The situation with you strobe wire could be worsened by reradiation.
You have just about 1/4 wavelength of wire, near and parallel to the
dipole, before making a bend to run fwd along the fuselage. This
causes an out-of-phase component to be added to transmitted RF, doing
wonders to
audio modulation. I've observed where you can hold (i.e., connected
to nothing) a whip-type comm antenna one foot and parallel to an
antenna under test, and watched the VSWR drop to zero. IN this case,
-0- VSWR not good, as bad things are happening.
Regards,
Fred F.
> A word of caution. I fitted a dipole aerial in the fin and tuned it with a
> VSWR meter to give the strongest signal in the mid-range. I subsequently
> fitted a strobe at the top of the fin. Recently I have found that ground
> stations with mid-range frequencies have had difficulty in receiving my
> transmissions. I checked the aerial again only to find that the mid-range
> was by far the worst sector.
> ....
> Roger A. (G-BXTD)
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