NIST Technical Note 1337: Characterization of Clocks and Oscillators

7. PHASE NOISE AND AM NOISE MEASUREMENTS 279... -120IE'"~ -140-160"kTB"-1800.01 0.1 1.0 10 100 1000 10,000FREQUENCY IkHzllalDELAY­LINErf BRIDGEDISCRLO6 dBmCONV. LOSS ~NF " 7 dBIbJFIG. 21 (a) Noise contribution analysis: (b) phase noise test setup using a delay-line rfbridge discriminator (rf = 2.8 GHz; O.termlnation POints. NF. noise figure: LF.low frequen~y.(From Seal and Lance. 1981.)NF ~ 2-3 dB as expected, i.e., the first stage noise predominates. The lowfrequencyend at 20 Hz gives an NF of 26 dB, which overall is quite an improvement.[n trace number 3 the mixer is included with it's rf (signal) port terminated.It is clear from this trace that certainly up to 100 kHz, the noise generatedby the mixer diodes being" pumped" by the LO signal dominates. This caserepresents the" classic" delay-line discriminator. The last trace (number 4)includes the low-noise, high-gain rf amplifier that can be used because thecarrier is suppressed in the delay-line rf bridge discriminator, in contrastto the classic delay-line discriminator case. This trace shows that from 1 kHzon up the measured output power is flat, representing a 2-3-dB NF.At about 20-40 Hz, trace numbers 3 and 4 begin nearing their crossoverfloor. In this particular case, which is discussed in full by Labaar (1982),the measurement systems noise floor (resolution) has been improved by40 dB.Figure 22 shows plots of phase noise as measured at two frequenciesusing delay lines ofdifferent lengths. The delay line used measure at 600 MHzTN-230