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Tektronix 7L12 Spectrum Analyzer Question

I'm in the market for a used spectrum analyzer like the 7L12 or the HP 141-T. One important use will be to make two-tone IMD measurements on HF SSB transmitters. I am concerned that with tone separations on the order of one kHz, the 7L12 may not have sufficient bandwidth in the 300 Hz mode to resolve adjacent IMD products expected to differ in amplitude by 40 dB or more.

Has anyone on the group used a 7L12 for this purpose and is the 300 Hz RBW sufficiently narrow?

There seems little doubt that the 141, with 10 Hz or 100 Hz RBW, will handle this.

Many thanks in advance.

Chuck NT3G

Reply to
chuck
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It wouldn't be ideal for 1 kHz spacing. If the -6 dB point is 300 Hz, and the shape factor of the 7L12's filters is about 8:1 like other Tek analyzers I've used, then the -60 dB point is around 2.5 kHz. Figuring a linear falloff (in log space), 1 kHz tones couldn't be resolved below about 30 dB, give or take 10 dB at the most.

I've never used a 7L12; maybe the filters are steeper than that. But you can't beat an HP 141T / 8553B / 8552B (not -A!) combination for HF work at less than 3x the price. If you've got the space, that's the way you should go.

-- jm

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Reply to
John Miles

Thank you, John.

FWIW, Tek claims a 6/60 dB shape factor of "4:1 or less" at all bandwidths on the 7L12. They're analog filters and after

30 years may not live up to their design specs. In the end it strikes me as insufficient headroom for an instrument requiring that kind of investment. I'll probably do the right thing and find an HP 141-T.

Thanks again, John.

Chuck

John Miles wrote:

Reply to
chuck

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