Tektronix 492 spectrum analyzer...is this normal?

I've recently acquired a fine condition Tektronix 492 spectrum analyzer. I've been hoping to finally get one in my price range for a long time and finally it happened.

It's in great shape and as far as I'm able to determine, it meets specs. It detects signals down to about -123 dBM, when at minimum span and max resolution. (It has the 100 Hz resolution option, lucky me! And the calibrated prescaler and digital storage options. Options 1,2, and 3, a very desirable configuration.)

The only thing that I think isn't quite right about it is that in three band ranges, 0 to 1.8 GHz being one of them, when in the FULL SPAN mode, the full span isn't displayed across the full width of the CRT.

The full span IS displayed, but it's compressed to fit in only part of the CRT's available width. The 0-1.8 GHz band starts at the left edge of the CRT and extends only to the midpoint. From the midpoint to the right edge, the trace is at the bottom of the CRT and is a flat line.

On the highest frequency range (the one that ends in 22 GHz), the same thing happens but in reverse. The trace is flatlined at 0 from the left side of the CRT to the midpoint, and from the midpoint to the right side edge, the band is displayed.

On the range that includes 5 GHz, it exhibits a similar problem but not so severely. The first 10th of the screen width (1 division) shows the flat line at 0 but the other 9 divisions show normally.

Does anyone have any information on this particular phenomenon? I have a hard time believing it's supposed to do that, not when all the other band ranges are full width across the screen when at full span.

This problem ONLY occurs at the full span setting on those three bands. In all other span settings, in any band, it'll display the full width trace as you'd expect it to.

Any info or help on this would be appreciated.


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Chris Johnson
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