" Tuuk" wrote in message
...
Hi
I have the MFJ 989C, and I am noticing that I can tune antenna to low SWR
but I also have noticed that the SWR often was jumping or spiking and very
unusual. I thought it may be coax or antenna or a short but then I noticed
also that the inductance coil is very sensitive. If you touch it or tap it
this will cause the SWR to spike. Also when it spikes, if you put a little
pressure on the Inductance coil knob it will solve the problem. Anyone
else
have situation such as this? What did you do to fix the problem? I opened
it
up and cleaned the contacts where I thought the problem was but still
didn't
correct the problem.
Any ideas ???



1. Check the contacts that you _don't_ think are the problem. Just because
it's a roller inductor doesn't mean that you're not the victim of a
garden-variety cold solder joint or a loose rivet. I'd check the whole
current path from one solder joint to the other (including the other moving
contacts -- there's a slip-ring _and_ a roller, yes?).

1a. You might want to try measuring resistance while you wiggle the thing
to see where the problem is. This can be difficult and frustrating, but if
you manage it you'll know for sure where the problem is.

2. _Only_ after you've verified that it isn't something else, see if you
can increase the contact pressure on the questionable joint. I'd think long
and hard before I did this on my own equipment, because it'll make it wear
out quicker.