Ok this is going to be simplistic.

I have a CW-80 special and some 19M of 50 ohn coax running to the back
of either a MFJ tuner or directly into the TS-850.

If I screw the shield on the pl259 plug tight onto the chasis socket
then I receive no signals, if I leave it loose but touching I receive
signals. Firest thought a short in the co-ax. Ohm meter reading shows
infinite reading so I assume (rightly or wrongly) no short.

I then took, as an experiement, my 2m areial co-ax, plugged it in and
tuned to a good local MW signal. Exactly the same phenomena occurs.

I transmit fine on 2m. Using the CW-80 I can sucessful transmit when
the plug is loose but I may be getting some rf leak as Mixw is pickin
gup stray characters in transmit strings.

Kust as an experiement I plugged in my RX320 and exactly thesame
phenomena.

Now I am still very new but I also note that the ohm meter across the
socket on the TS850 shows 50 ohm which I guess is corect though the
mobile 2m transmitter shows infinite.

So the botom line is I am struggling to find the cause of the problem.

Any clues?