As a good "in-betweener" an all-mode receiver works very well at locating
spurs and measuring relative strength.
I use an IC-R8500 which covers 0.1MHz to 2GHz.  A scanner can be a big help,
or if you're not running very fast (3rd harmonic below 30 Mhz) a shortwave
radio works well.

The Icom receiver actually does a better job at finding bus hash noise than
the HP EMC analyzer we rented for a month. Of course renting the HP device
cost almost twice what the receiver did to purchace.  The HP rep told us,
after we gave up on the instrument, "yeah, it dosen't pick up pulsed noise
very well...."

A small loop antenna made from a BNC cable will help you localize the
noisemakers.