Richard, getting clear details is like drawing teeth. I suspect the RV
might be fibreglass, and so about as RF transparent as you might get.
Further, something hints to me that the grounded ATU is on top of the
ladder, so it isn't really grounded.

But in the absense of clear details of a single scenario, I can't help.


In my previous experience in newsgroups, I'll agree that getting
details from those who pose questions here is difficult, and I guess I'm
as guilty as the rest. However, my original question was regarding
details of common mode choke filter design and has apparently morphed
into my RV setup.

The RV is a 31' class C, all fiberglass shell, welded aluminum
frame, on a Ford E450 chassis and cab up front. Although I realize there
are many aspects that could cause RFI in the cab area of the motorhome, I
merely wanted to use a choke filter to see what improvement might take
place.

The SG-237 tuner does not use a control line, so no filtering needed
here. The DC will be pulled off the back of the motorhome close by, and
that source, as I previously mentioned, will also be routed through a
common mode filter.

The antenna feedpoint / loaded base area is about three feet down from
the top of the metal ladder. The metal ladder vertical rails is one
piece construction, and is bonded at bottom of both rails with 2" tinned
copper braid to the main chassis rails with pieces running about 22"
length. All in all, about as good a ground as can be obtained under the
circumstance.


Ed