Filip
What exactly are you trying to measure?
A phase-modulated carrier will have an infinite number of sidebands
spaced at the modulating frequency, the amplitude of the sidebands
gradually reducing away from the carrier. The amplitude of the 1st
pair of sidebands (closest to the carrier) is a function of the
modulation index. In your case the 10MHz carrier signal has it's phase
modulated by +/- 1 rad, at a rate of 10kHz. Note that the level of the
carrier is itself a function of the modulation - i.e. as you change the
level of the peak deviation, the level of the carrier will change. With
1 rad deviation, the carrier will be approx. 2.3dB down compared to with
no modulation.
So, if you want to measure the phase noise of the 2024, then you should
turn off the modulation.
Are you getting confused about the dBc/Hz measurement? 'dBc' means 'dB
relative to the carrier' - that's why it's called dBc. dBc/Hz is
usually used for noise measurements only, and means the level of noise,
relative to the un-modulated carrier (in dB), if measured in a 1Hz
bandwidth, at a given offset from the carrier.
The level of modulation sidebands is independent of measurement bandwidth.
I may have missed something here - please could you give more details of
what you are trying to do?
regards
Grant
Date: Mon, 14 Jan 2013 11:35:02 +0100
From: Filip Amator <filip.ama...@gmail.com>
To: time-nuts@febo.com
Subject: [time-nuts] 5120A and PM singal
Message-ID:
<cabztljcz+vht+ehijzgm0uky_lio9yzphogxngmg7yap4rt...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Hello,
I made a simple measurement using Symmetricon 5120A phase noise
measurement set and a Marconi 2024 signal generator and I don't
understand the results. I measured the phase noise of 10 MHz signal
with 1 Rad phase modulation at 10 kHz, and I got from mesurement peak
at 10 kHz with level about -26dBc/Hz. According to the current
definition of dBc/Hz, the value of -26dBc/Hz should be considered as a
-26dB of modulation relative to 1 Rad. But I would expect that the
peak level will be at 0 dBc at 10 kHz. Does anyone knows how to
explain this difference?
Filip Ozimek
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