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Phil Allison[_4_] Phil Allison[_4_] is offline
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wrote:

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This is widely known. It is also widely known that it is difficult
to specify a NF for an amplifier,


** Not true.


please explain how the 3.3Kohm source resistor you arrive at by doing this improves the noise



** It does no such thing, I made no such claim.


Since the SSM has a higher input noise current density and would therefore give a lower resistor for this calculation, does this mean better amps have higher input noise current densities?


** JFETs have very low noise currents so noise voltage dominates with low input resistances.

The ratio of an amp input voltage noise and current noise densities does
not define a "input noise resistance" from which you can calculate anything.


** So there is a big hole in your imaginary knowledge.


Putting in a 3.3K resistor as you want will not give best noise
or NF but will increase noise several fold.


** Of course - lowest noise is with a dead short.

NF is tested with a real input load and is a figure of merit in dB for that condition. So many dBs more noise than if the amplifier were noise free.

So there will always be a resistor value that minimises the noise rise in dB.

Why do I have to explain this concept?



https://pdf1.alldatasheet.com/datash...MI/2N4403.html

See figure 9 showing a set of curves for Ic, resistance at the input and NF.

For 1mA and 500ohms the NF is under 1dB at 1kHz and beyond.

At lower currents, the best noise figure is at much higher resistances.


Expected.


** It is the same claim you disputed before.

What happened to the link to Project 66 ??

My published design with full tech details.

To much for you puny brain ?


FFS go away dickhead.



There you go again. What's the deal?


** You are a lying idiot.

If I had your name I would make a very strong complaint to TI.

See if you really work there and in what role.

Coffee boy maybe?

Work experience kid ?

Nasty little ****, whatever the fact.


.... Phil