In the FM BCB band I get what look like FM signals at between -100 and -110 dBm.
More curious are 7 spurs between 250 and 375 MHz , all stronger than -90 dBm.
One spur, at 360 MHz, is at -58 dbm - even if I narrow sweep just to 359.99 to 360.01 MHz, with Ref level at -30 and range set to 100 dBm. It's an impulse-like filter, with nearby frequencies all at -120 dBm.
(A GIF screenshot is attached.)
Not what one expects with the antenna disconnected...
I tried some ferrites on the USB line, and they may have helped marginally, but spurs are still loud and clear.
- 360 MHz spur, no ant.gif (136.6 KiB) Viewed 3686 times
...It's an impulse-like signal...
attached is another screenshot - a 500 MHz sweep, again with no antenna connected.
- 500 MHz sweep, no antenna.GIF (150.17 KiB) Viewed 3685 times