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OK I looked up the 8553 manual and it suggests your analyser has a 24dB noise figure. So this will make it very difficult to see a small improvement in NF of the first amplifier stage in your CB radio unless you add a preamp in front of the 8553.

Why not punch some numbers into a gain/noise spreadsheet to see what I mean?

i.e. model the analyser as a high gain stage (with 24dB noise figure) and place it after the RF amplifier.

You will see it will not be able to display a 2dB reduction in NF of the stage before it because it is so deaf. i.e. the noise floor won't drop 2dB if you drop the NF of the RF amplifier by 2dB.
However, if you place a preamp in front of the analyser then you will find it will be MUCH easier to measure (and quantify) any NF improvement in the CB amplifier stage.

You would have the same problem (possibly slightly worse) if you used the HP8566B as it has similar sensitivity to the 8553?

<blockquote data-quote="G0HZU" data-source="post: 410924" data-attributes="member: 19109">OK I looked up the 8553 manual and it suggests your analyser has a 24dB noise figure. So this will make it very difficult to see a small improvement in NF of the first amplifier stage in your CB radio unless you add a preamp in front of the 8553.Why not punch some numbers into a gain/noise spreadsheet to see what I mean?i.e. model the analyser as a high gain stage (with 24dB noise figure) and place it after the RF amplifier. You will see it will not be able to display a 2dB reduction in NF of the stage before it because it is so deaf. i.e. the noise floor won&#039;t drop 2dB if you drop the NF of the RF amplifier by 2dB.However, if you place a preamp in front of the analyser then you will find it will be MUCH easier to measure (and quantify) any NF improvement in the CB amplifier stage.You would have the same problem (possibly slightly worse) if you used the HP8566B as it has similar sensitivity to the 8553?</blockquote>

[QUOTE="G0HZU, post: 410924, member: 19109"] OK I looked up the 8553 manual and it suggests your analyser has a 24dB noise figure. So this will make it very difficult to see a small improvement in NF of the first amplifier stage in your CB radio unless you add a preamp in front of the 8553. Why not punch some numbers into a gain/noise spreadsheet to see what I mean? i.e. model the analyser as a high gain stage (with 24dB noise figure) and place it after the RF amplifier. You will see it will not be able to display a 2dB reduction in NF of the stage before it because it is so deaf. i.e. the noise floor won't drop 2dB if you drop the NF of the RF amplifier by 2dB. However, if you place a preamp in front of the analyser then you will find it will be MUCH easier to measure (and quantify) any NF improvement in the CB amplifier stage. You would have the same problem (possibly slightly worse) if you used the HP8566B as it has similar sensitivity to the 8553? [/QUOTE]

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