SA44B Generating Noise

[bbowar]

We are doing a comparison of channel power measurements between your USB-SA44B and another manufacturer’s spectrum analyzer (SA). We noticed that when the Signal Hound was turned on we started seeing a signal well about the noise floor on the other manufacturer’s SA. The two spectrum analyzers were connected to a common signal source using a combiner. We then connected the input of the USB-SA44B to the input of the other manufacturer’s SA. We then saw what looks to be a sweeping CW signal at an amplitude of -45 dbm on the other manufacturer’s SA. Is this normal? Is there something we can due to minimize this noise?

[Justin Crooks]

BBowar,
The USB-SA44B has higher LO feedthrough than other models we sell, and the LO is offset by only 10.7 MHz. You can minimize it by setting a reference level around -30 dBm (which will turn on the RF preamplifier), or manually turning gain to 1, preamplifier on, attenuator to 10 or 15 dB. This should reduce the LO feedthrough to around -60 dBm (typical).
Choosing a product like the BB60C will keep LO feedthrough below -80 dBm, and will keep the LO > 1.2 GHz away from the RF.
You can also add a circulator, ore even an external attenuator and/or preamp, to reduce LO feedthrough if needed.

[Author]

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