Javier - I believe you are indeed close. With the IF BW at 1 MHz the correction is indeed 60 dB. The post detection filtering by the video filter only makes it look nicer but does not come into play. I believe there are two correction factors that you need to take into consideration, that, as I recall, comes close to about 2.5 dB total. I may be off on that number, but, it is close to that (I am sure you can Google it). You will read more because the filter BW is off course not perfect, and the equivalent noise BW is greater than 1 MHz. I believe there is a correction for that. The other, is how the detector inside the analyzer treats noise instead of a pure sine wave. Those corrections will get you closer to your expected value, and, maybe the others are due to your losses. 73 - Mike
Mike B. Feher, EOZ Inc. 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 (B) 908-902-3831 (C) -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Javier Herrero Sent: Saturday, October 22, 2011 8:51 AM To: Discussion of precise time and frequency measurement Subject: [time-nuts] Noise source measurement Hello all, Perhaps a bit OT, but I'm measuring the output noise density of a noise source at a puntual frequency. I've fed the noise output to a 8566B spectrum analyzer, BW set to 1MHz and video BW set to 1kHz so the displayed trace is flat. I obtain a measurement of -45dBm, and I understand that the noise density then is -105dBm/Hz. From design variables, I was expecting a somewhat lower value, around -110dBm/Hz, but between the NoiseCom noise source and the output there are several things (attenuator, filter, amplifier, directional coupler, variable attenuator, ...), so perhaps there are slight differences between estimated insertion gains and losses accumulate up to 5dB. Before dismount the system and look directly at the noise source output and measure the losses/gains of each element, I would like to know if I am doing this mesasurement right or am I commiting some mistake? Thanks! Best regards, Javier, EA1CRB _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
