Re: Airspy noise figure

Marcus D. Leech <mleech@...>
 

On 03/11/2018 09:00 PM, David Rowe wrote:
Thanks Dave - sounds like you have a great experimental set up there for NF measurements. For anyone interested in NF measurements, I've blogged on my humble experiments here:

http://www.rowetel.com/?p=5867

I mentioned your results in the post Dave, hope thats OK.

Cheers,

David
I'll point out that single-point noise-figure methods are rather error-prone, which is why the industry has standardized on the Y-factor method, in which
you have TWO sources of known noise power distribution.

For noise figures above 3dB, you can usually use a high-quality terminator at room temperature -- whose PSD will be -174dBM/Hz, and then a calibrated
noise source, usually in the 20-35dB ENR range. You take averaged measurements of both, and use that to determine the noise figure of the DUT.

Once you start going to noise-figures below 2-3dB, it's better to have a "cold load" as one of the noise sources. Labs that care about noise figure
measurements for "good" LNAs usually use an LN2-cooled load for the "cold" load, and again a calibrated noise head for the "hot" load.





On 12/03/18 10:18, David Eckhardt wrote:
I have a calibrated noise source good to 18 GHz and several precision attenuators (HP, both single value and switched). Knowing the noise output of the noise source, I attenuate until the noise just goes into the 'noise', tangential noise. The difference between the noise source known output and the attenuation is my noise figure.

Dave - WØLEV

On Sun, Mar 11, 2018 at 10:27 PM, David Rowe <david@... <mailto:david@...>> wrote:

Thanks Dave,

Could you tell me a little more about how you measured NF?

Thanks,

David

On 12/03/18 08:37, David Eckhardt wrote:

I've measured both the R1 and my present R2. They both come in
around 4 dB. I believe 7 to 8 dB is a bit much based on my
experience with them.

Dave - WØLEV

On Sun, Mar 11, 2018 at 9:34 PM, <david@...
<mailto:david@...> <mailto:david@...
<mailto:david@...>>> wrote:

Hi - I've been setting up a system to measure noise figures
of SDRs
in real time, an extension of some similat tests we
performed a few
years ago:

https://www.rowetel.com/?p=5057
<https://www.rowetel.com/?p=5057>
<https://www.rowetel.com/?p=5057 <https://www.rowetel.com/?p=5057>>

I'm getting a NF of 7-8dB for a new Airspy R2 and Airspy
mini. The
spec quotes 3.6dB. Has anyone else measured the NF?

I note the 3.6dB figure is exactly the same as the front
end tuner
R820 tuner. However a system noise figure will always be
poorer
than the front end device.

Thanks,

David




-- *Dave - WØLEV
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