> I am running 2, 1/4wl verticals,spaced 3/8WL apart (my car roof is
> only so big) and feeding each antenna with an equal length of RG8X
> (116" I think) I have a spdt switch with a jumper across the common
> and one side(to make it a spst in actuality), so one antenna is ALWAYS
> connected direct to a short length of RG8X to the rig. I then have a
> 1/2WL of rg8x (77" aprox) which I short out or open up, introducing a
> 180degree phase shift. No matter how many times I check and double
If you short the ends of the 1/2 wl of cable together with a perfect
short, you should have what appears as a short across the main
transmission line! What that does is form two 1/4 open stubs that
parallel the main transmission line, and each open 1/4wl line acts
like a short between the shield and center at the connection point.!
I don't see how that ever worked on any band.
What you need to do is switch that line out, and that takes a DPDT
switch.
It also doesn't sound like the line is correct, because it looks like
you used solid poly dielectric velocity factor of .66. A free-space
half-wave is about 118 inches on six meters, and the Vf of most
RG8X I've measured is about .75. .75 times 118 is 88 inches, not
77 inches! That still is a small error, unless the particular RG8X
you have has a lighter foam than most RG-8X cables I have seen.
In that case the error is larger.
By the way, while it is true that solid poly cables are about .66 Vf,
foam cables vary widely in Vf. I have cables as high as just above
.9 Vf, and as low as .75 (the RG-8X I have)!
Another problem is a 1/4 wl vertical over a reasonably good ground
is about 35 ohms, and so there are usually standing waves in the
system. With mutual coupling the antenna base impedances will
be different than for a single antenna...but you have a BIG problem,
because of the switch wiring.
73, Tom W8JI
W8JI@contesting.com
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