Thread: Noise Source
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Old 23rd May 2022, 4:48 pm   #37
G0HZU_JMR
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Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
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Default Re: Noise Source

I guessed the noise figure based on the datasheet for the SSA3021X plus model as it quotes a displayed average noise level (DANL) of -161dBm/Hz.

-161- (-174) = 13dB

Also your noise floor plot showed a DANL of about -110.4dBm in a 100kHz bandwidth (= 50dBHz) so this would be -110.4dBm - 50 = -160.4dBm/Hz although I haven't included any corrections in this for log amp or detector type.

It's best to make a two stage amplifier rather than try and use that NXP part. The NXP part also has poor input VSWR so it isn't really suitable for use as a noise figure analyser preamp. The limiter could be something as simple as some back to back diodes.

Avago application note 1050 shows a few diode limiter designs using low cost PIN diodes. The alternative is to use back to back 1N4148 silicon diodes although the 1N4148 diodes will only provide effective limiting up to about 500MHz.
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Regards, Jeremy G0HZU
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