Tom, I just recently ran into an interesting situation that might relate to
why your problem developed or got worse over the last week or so. My new
loop antenna that my Son and I put up a few weeks ago was working really
great here, and then, suddenly, my SWR changed and at one point, I couldn't
load up on any band. I checked out everything on my rig and in the shack and
I couldn't find anything. At first glance at my antenna, it looked OK; at
least to my wife's eye. However, when I got my Son to come over and really
look at it more carefully, he saw that the antenna was hung-up on the bark
of a tree limb in one place. That doesn't seem like it should have effected
my antenna all that much, but he pulled it away from the tree, tightened it
up on the pulleys, and when I checked it out with my rig, everything was
working again just fine.  Evidently, the high wind, the snow, and the ice
caused the tree limb to blow around enough to come down on my antenna and
mess it up. My point is that it doesn't take much sometimes to change your
match and to cause an increase in SWR, common mode currents, etc. 

Ron, K8HSY 

-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Tom Behler
Sent: Tuesday, February 23, 2016 6:11 AM
To: [log in to unmask]
Subject: Re: RFI problems.

Tom:

This is all very helpful information, and please thank your friend for me.

Based on what is said here, I'm not quite sure what the easiste and/or most
practical steps will be to help with this problem, other than RF chokes, and
perhaps a line isolator or two.

Why the RFI has manifested itself strangely over the past week is still a
mystery to me, because I have not changed anything in my shack setup.
Perhaps something has changed outside, which I haven't pinned down as of
yet.

Will keep at it here as I get time, and I will keep everyone updated.

I appreciate everyone's help.

Tom Behler: KB8TYJ


-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Tom Fowle
Sent: Monday, February 22, 2016 10:17 PM
To: [log in to unmask]
Subject: Re: RFI problems.

I got an answer from my engineer friend, but havn't yet got his permission
to forward the entire answer.

His basic thinking is that we need to think in terms of fields, not current
flow and that fields flow outside but near conductors not in them.  Fields
will flow between conductors, E.g. in coax because this provides a low
impedance path.  This is hard stuff to follow, particularly in practical
terms.

He says, as we  should know, that ground systems don't work at frequencies
much above power line frequency and thus are of no use in keeping R.F. out
of where we don't want it.

It would seem that the quality of coax shield, and the location and
directivity of antennas away from susceptable devices are the main methods
of controlling field flow.  Of course most of us can only do so much along
these lines in the real world.  

BTW, in testing cables, one thing we can do if we have an accessible power
meter and a dummy load is to run a little power through the cable in
question to a dummy  and see how much power we get back. This has been
discussed recently in QST. If a cable shows loss that power has to go
somewhere, either heating the coax or leaking into the free space around the
cable.

My friend Ralph, has the 6Th eddition of his book on "grounding and
shielding" comming out from Wiley in April.  When it's out, I'll request it
from Bookshare and see how much can be made of it.

Undoubtedly Bookshare won't make the diagrams accessible, but perhaps the
text will help.

tom Fowle WA6IVG