[Amps] Checking for IMD

[Tom W8JI]

> The problem with most of the cheaper spectrum analyzers is 
> that they don't
> have enough resolution. For IM measurements you need a 200 
> or 300 HZ
> bandwidth filter and enough stability to sweep only a few 
> khz of the
> spectrum at a time. Even some of the moderately priced 
> units will not do
> that. The old HP141 will do it but even it has stability 
> trouble with the
> 1.2 ghz rf head in it. You really need the 110 mhz rf 
> front end in it so it
> is stable enough for the narrow sweeps needed to look at 
> close spaced tones
> used for IM measurements.

I was going to suggest the very same thing. I can verify 
what Gary says.

If you get an old analyzer be very careful. Even the better 
of the old analyzers, like the HP141, requires a narrow 
frequency range RF section to be useful.

There are a lot of analyzers out there that won't read IM 
products well. The dynamic range of the HP141 is about 50dB 
before it falls apart, so it is a marginal instrument even 
for TA measurements of harmonics.