I doubt that the FCC has the inclination, desire, or resources to try
to forbid or limit the use of antenna analyzers. If they did, they'd
have to start raiding labs all over the country and confiscating
multi-thousand-dollar vector network analyzers, S-parameter test sets,
and so forth.

A network analyzers is not marketed as an antenna analyzer, or even an
intentional radiator for that matter. I have a signal generator, an
amplifier and an antenna in my lab but it does not mean I can sweep the
entire LF to UHF bands at any wattage.

For a fourth: they *might* also qualify for legal use under Part
18 (Industrial, Scientific, and Medical Equipment). These devices can
also operate in most frequency bands (although there are several
subbands which are specifically authorized for them and are thus
recommended), subject to maximum-field-strength limits similar to
those specified for Part 15 devices.

I was just looking through Part 18 and it really is unclear to me, however
one thing was clear to me, ISM devices are prohibited for use in certain
bands. One of which is search and rescue. So now how can I test my ELT
antenna installation on my aircraft if I'm violating FCC rules?

Thomas