"Teri Buck" wrote in news:44XFh.4$mI6.3@trndny08:

I am using a multi-switch to change radios and antennas. One of those
MFJ 1700Bs. I get different SWR readings depending upon where I place
the bridge in the tangle of wires that go into and out of the switch.

Teri, some thoughts:

For practical transmission lines and antennas, the VSWR decreases
smoothly from load to source, and the rate of decrease depends on the
transmission line (one way) loss and is predictable.

For example if the VSWR is 1.5 at a certain point, then at another point
closer to the source and where the one way cable loss is 1dB to the first
point, the VSWR will be 1.4.

So, if you are truly making VSWR readings without changing the line
length, you should expect the readings to decrease towards the generator,
but the decrease for practical lines will be quite small. If you observe
otherwise (higher or lower) something else is happening.

A well designed switch should not change the VSWR much on the through
leg, so measurements either side of it should be similar.

If you are changing line length as well as moving the VSWR meter (just to
complicate issues), a likely contiribution is that the outside of the
outer conductor is influencing the load seen at the load end of the coax,
ie the cable is carrying current on its outer (which is often
undesirable).

If I take the switch out of the equation I get very low SWR. With it
in I get 2.5:1.

Is this on only one antenna, or are you generalising and oversimplifying
things?

In taking the switch out, have you disconnected the cable outer
conductors whereas they would have all been bonded at the switch?

What does the switch do with the non-selected antennas, does it ground
them? Grounding the end of the feedline to the unused, but mutually
coupled antenna may inflence the load presented by the selected antenna.

Have you checked all the components in your "tangle of wires". Are there
faulty cables, or loose connectors (especially if you are using UHF
connectors).

The answers to these questions might throw light on what is happening and
whether choking will fix it.


All of the coax has a common ground so the OCF windom also shares a

Well, you know that the "OCF Windom" (aren't they all off centre fed)
depends on a radiating feedline. Perhaps you mean one of the newer
designs with coax vertical that are designed to have common mode current
on the vertical part, then you try to restrict that current at a point
where you decide the coax is to be feedline and not radiator, which is
easier said than done.

....

Owen