Well, they could be either a self-contained meter; one that one hooks up
directly, inline/series, with the RF current and the other is as you
have described. If the meters are not of the sealed type, you can
remove the movement from the shell and have a look. Try and see if
there's a thermocouple mounted somewhere as an integral part of the
unit. Meters, like on the TCS, BC-191/375, and the ART-13 for example,
are self-contained. They generally all work the same, its just where
the thermocouple is located. That's my observation on the subject.....

terryS wrote:
Came across a couple of those RF antenna current meters. Typical they
have a scale up to three of five amps. One is US and other is UK war
surplus.
AIUI the meter movement is driven by a small DC current produced from
the output of the thermocouple.
The thermocouple being heated by the RF current. Looks like the meter
itself is a one or five milliamp movement. Can anyone comment/advise?
Thanks.