That is why I asked what the Po was. Where did the 177 come from? L(f) is single sided. This is not my first "rodeo" in these matters. 73 - Mike

Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 office
908-902-3831 cell

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of John Miles
Sent: Thursday, August 11, 2016 4:22 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] State of the art of crystal oscillator measurements

Remember that L(f) is expressed in dBc/Hz, not dBm/Hz.  If it were dBm/Hz, then kT would be the limit.  But in dBc/Hz terms, the limit is 177 + the DUT's output power in dBm.

Assuming a 50 ohm system, of course.

-- john, KE5FX
Miles Design LLC

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-177 = the -174 dBm/Hz SSB thermal noise floor at 25C, less 3 dB to account for the usual assumption that half of it is AM, half PM.

dBm/Hz is obviously equivalent to dBc/Hz for a 0 dBm carrier.

Anyone who claims to measure noise in a 1 Hz bandwidth below -177 dBm/Hz at room temperature is either doing something wrong somewhere, or doing something amazing somewhere.

-- john, KE5FX
Miles Design LLC

That is interesting. We always used -174 and not -177 as it was concluded that at those low levels AM and PM noise are not discernible, so, the total noise density per Hz was -174. This must be relatively new since I worked in industry. We had a bunch of PhDs from Lincoln helping as well and they always used -174. This sounds like one of those instrument manufacturers gimmick to make the numbers look better :).

Your last statement is why I started to question the claims initially. - Mike

Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 office
908-902-3831 cell

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of John Miles
Sent: Thursday, August 11, 2016 7:57 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] State of the art of crystal oscillator measurements

-177 = the -174 dBm/Hz SSB thermal noise floor at 25C, less 3 dB to account for the usual assumption that half of it is AM, half PM.

dBm/Hz is obviously equivalent to dBc/Hz for a 0 dBm carrier.

Anyone who claims to measure noise in a 1 Hz bandwidth below -177 dBm/Hz at room temperature is either doing something wrong somewhere, or doing something amazing somewhere.

-- john, KE5FX
Miles Design LLC

time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.