New USB-SA44B, Large Spurs in UHF Band

Just unpacked a SA44B and VSG25 unit to try out the software and get up and running for a calibration application we’re planning on using these form.

I wanted to check to see if the following spurs were expected in the SA44B spectrum. I see this with a terminated input, and see these spurs only in the low center frequency range up to 1.1 GHz.

When I disable spur reject, a few other, less-powerful spurs appear, but the ones in the screenshot remain regardless of this setting. I tried a number of RBW, spans, and center frequencies.

We can still do what we wanted with these spurs, but I wanted to see if this was expected behavior or if I’m missing a calibration step somewhere. Thanks!

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Ryan,
Unfortunately, spurs like this are normal for the USB-SA44B. The frequency is usually a little higher, but it depends on your cable lengths and computer. It looked like your spurs peaked around -100 dBm with a -30 dBm reference level for a 100 MHz span.

When you use a span of 200 kHz or less, most of these spurs will be drastically reduced or eliminated. This is because the SA44B mixes differently for narrow spans.

Thanks for the speedy response, Justin! It’s still a great tool at a great value; just about all our intended test signals will be much stronger so we’ll work around it.

FWIW, it would be nice to know about this, a-priori. I probably just didn’t understand the implications while reading the manual/specs.

For the record, does the BB60C also suffer from this issue or would it give you a nice, flat response down to the noise floor, particularly in the sub-GHz range?

The BB60C residual responses are specified to be below -106 dBm, are typically below -110 dBm (at -50 dBm ref level) and most of them go away when you turn “spur reject” on. Unfortunately, it is difficult to do much better at our price point, and impossible to eliminate spurious / residual responses entirely, at any price.

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