Tom G3OLB,

Talking of TS-850s, does anyone know why my TS-850 changes gain at
500.000 KHz? Seems like an attenuator is switched in above 500 KHz. Is
there a mod to defeat it?

The TS-850 is manufactured with an attenuator for the MF AM broadcast band
(included within that band pass filter).  The attenuator is made from
surface mount resistors, on the underside of the PCB, so it is a fairly
tricky job to rework.  If you do a web search for TS-850 mods, you will find
a text and figures as to how to remove the attenuator.

73, Bob ZL2CA