Noise figure and Volts/rtHz

[George Herold]

This Jfet lists noise figure as 2.1 dB, how do I turn that into v/rtHz ?
Is the reference a 50 ohm resistor? So 3dB would be twice the voltage noise
density of a 50 ohm resistor?

https://www.onsemi.com/pub/Collateral/ENA1965-D.PDF

Thx,
George H.

 

[John Larkin]

On Wed, 18 Sep 2019 10:59:31 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

This Jfet lists noise figure as 2.1 dB, how do I turn that into v/rtHz ?
Is the reference a 50 ohm resistor? So 3dB would be twice the voltage noise
density of a 50 ohm resistor?

https://www.onsemi.com/pub/Collateral/ENA1965-D.PDF

Thx,
George H.

That was likely measured at 100 MHz with optimal narrowband tuned
matching networks on input and output, so there's no clear correlation
to equivalent voltage noise.

Buy something else, properly specified.

 

[George Herold]

On Wednesday, September 18, 2019 at 2:06:53 PM UTC-4, John Larkin wrote:

On Wed, 18 Sep 2019 10:59:31 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

This Jfet lists noise figure as 2.1 dB, how do I turn that into v/rtHz ?
Is the reference a 50 ohm resistor? So 3dB would be twice the voltage noise
density of a 50 ohm resistor?

https://www.onsemi.com/pub/Collateral/ENA1965-D.PDF

Thx,
George H.

That was likely measured at 100 MHz with optimal narrowband tuned
matching networks on input and output, so there's no clear correlation
to equivalent voltage noise.

Buy something else, properly specified.

Well the other jfets (that aren't EOL) look noisy.
like this
https://www.onsemi.com/pub/Collateral/MMBFJ309LT1-D.PDF

or have a noise figure
https://www.onsemi.com/pub/Collateral/2SK3557-D.PDF


I already bought the cph3190... Hey it came really fast from DK. They now
have an option for USPS shipping. It's cheaper and faster than UPS ground.

ordered Friday, here on Monday.

George H.

 

Noise is a power thing. Doubling the noise voltage is 6 db . Doubling noise power is 3 db

 

[Phil Allison]

George Herold wrote:

-------------------------

or have a noise figure
https://www.onsemi.com/pub/Collateral/2SK3557-D.PDF

** The noise figure graph shows 1dB, rel 1kohm.

Equates to 12% more noise voltage than the resistor alone.


So: Noise of 1k ohms at room temp = 4.03 nVrtHz

Total noise = 4.5 nVrtHz

Noise fet = sqrt(20-16) = 2 nVrtHz.




..... Phil

 

[George Herold]

On Wednesday, September 18, 2019 at 7:15:33 PM UTC-4, Phil Allison wrote:

George Herold wrote:

-------------------------


or have a noise figure
https://www.onsemi.com/pub/Collateral/2SK3557-D.PDF



** The noise figure graph shows 1dB, rel 1kohm.

Equates to 12% more noise voltage than the resistor alone.


So: Noise of 1k ohms at room temp = 4.03 nVrtHz

Total noise = 4.5 nVrtHz

Noise fet = sqrt(20-16) = 2 nVrtHz.

Huh thanks Phil.
George H.

.... Phil