Nice unit and beautiful condition. But all that function and only 600KHz? I would have expected much higher bandwidth capability or am I missing something concerning it's intended use?
No you aren't missing anything. In the time period when it was developed (remember this is probably two decades ago) it fit a market niche in the lower frequency range that hp decided to sell to.
From the brochure -
"Broad sinewave
frequency coverage from 0.1 Hz to
600 kHz with 0.1 Hz resolution make
the 8904A ideal for a number of low frequency
applications.
...
All this unique capability makes the
8904A a powerful tool for demanding
applications like VOR, ILS, FM Stereo,
and communications signaling."