9

SL2015

Measurement of Phase Noise.

This is best measured by looking at the IF output of the

SL2015. The IF should be fed to a spectrum analyser, where

it can be interpreted.

There are two common methods of doing this:

a) using phase noise analysis software (such a HP85671A

phase noise program)

b) direct measurement of the noise floor at the chosen offset

frequency, and conversion to a dBc/Hz figure.

Since method a) will depend on the software used, a

description of method b) will be given only.

To measure phase noise at 10kHz offset:

a) tune the centre frequency of the spectrum analyer to the

IF - e.g. 479.5MHz

b) Set the span initially wide (10MHz or greater). Gradually

reduce this until it is set to 50kHz or less, taking care to ensure

that the centre frequency of the display matches the IF peak.

c) perform a peak search

d) set marker delta to 10kHz

e) set video averaging ON to ensure that a representative

measurement of the noise floor at the chosen offset frequency

is made.

f)

record the level of noise at the 10kHz offset compared to

the peak IF level (in dBc).

Measurement of Conversion Gain

(from a 50

a) Connect an RF signal generator to the RF input to the

SL2015.

b) Connect an IF output to a spectrum analyser.

c) Feed the SL2015 with the appropriate signal level,

depending on AGC setting, required output, etc.

d) Note the relative difference in the input and IF level in dB.

This is the conversion gain of the device.

For increased accuracy, the input signal level should also

be checked with a spectrum analyser, since any level

measurement errors that exist within the analyser will then be

relative, rather than literal.

The AGC voltage may be varied and conversion gain

measured at different AGC voltages.

Care must be taken to ensure that the LO is stable, since any

instability will reduce the averaged peak LO value, thus giving

a falsely low phase noise reading.

g) convert the measured reading to a 1Hz bandwidth.

e.g.

A measured phase noise of -50dBc/1kHz bandwidth

(RBW of 1kHz) corresponds to -80dBc/Hz.

Since noise floor must be reduced by the ratio of the two

bandwidths

i.e. 10 log 1kHz/1Hz = 30dB.