[Elecraft] Spurious Signals in KX3 and PX3

[Dauer, Edward]

Anyone have an idea where and how I might begin tracking this down . . .

KX3 (indoors with a Buddipole) has a signal every 18 Khz across almost all of the HF spectrum, worst on 15M.  It also appears on the PX3 display - in all the same places.  On both AM and CW it sounds like a buzzing, with about a 1+ Khz bandwidth..

The signal level changes on the KX3 as expected with PRE and ATT cycled.  On the PX3 display, PRE and ATT change the base level but not the absolute value of the peaks.

Here's the odd thing - the audible signal disappears from the KX3 when the antenna is removed, but it does not disappear from the PX3 - where, again, the base level changes but the magnitude above base level does not.  And it remains in the PX3 display even when the I/Q cable is removed.

Neither the KX3's NB nor NR change anything.

The KX3 is running from batteries, so it's not the outboard power supply.  Neither is it the PX3's wall wart, since the signals are present in the KX3 when that supply is removed from the source.

Unfortunately it will be a while before I can move the equipment to another location to see if that matters.  In the meantime, anyone know a signal source with harmonics at 18 Khz?

Tnx,

Ted, KN1CBR