Re: SDR-Console Power dBm Accuracy


jdow
 

It might help me "sketch out" a good apparatus if I knew target frequency and noise figure data. HF measurements might require something completely different from microwave measurements. The difference between 5 dB being ridiculously good to 1dB being somewhat noisy is "Yuge" (Picture man with orange hair saying that for best affect.)

{^_-}

On 20210624 09:39:00, Larry Dodd wrote:
Gedas,
Yes I agree it is exciting times.  Radio (SDR) astronomy is going to change drastically in the next few years.  Hope I live long enough to see some of it.
Larry, K3LED

On 6/24/2021 16:23:40, Gedas <w8bya@...> wrote:

Hi Larry, great ! I am glad the video was of value. It is nice to pass forward many decades of RF lab experience. I was one of a limited number of certified tempest engineers and had a very memorable career getting to work on some amazing systems and designs. As an aside I am also into astroimaging and have dabbled a bit with radio astronomy. As you said exciting times now that SDR have matured so much. Let us know how you make out. TTYL es 73.

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/24/2021 11:57 AM, Larry Dodd wrote:
Gedas,
Very nice detailed video. I have an HP 3400A and use it in same way you did but with an HP signal generator. Your Marconi SG is really nice. I have a TS-2000 also. Thanks again! Appreciate all the help. 
Larry, K4LED 

On Jun 24, 2021, at 10:36 AM, Gedas <w8bya@...> wrote:



Hi Larry. Have you considered deriving the NF from the MDS ? This is quite repeatable and accurate for detection systems that do not have extremely low NF's.

The same caveats apply requiring a calibrated sig gen and external step attenuator(s) with a calibrated true reading RMS meter. Commonly done in my past life in tempest engineering.

I generated a simple Youtube video illustrating the procedure if you think it is applicable to your needs. 73

https://www.youtube.com/watch?v=qPWXbodjVIA

Gedas, W8BYA EN70JT

Gallery at http://w8bya.com (under repair)
Light travels faster than sound....
This is why some people appear bright until you hear them speak.
On 6/23/2021 9:57 PM, Larry Dodd wrote:
jdow,
Thanks. We use a calibrated on/off noise source to do a Y Factor Method for SDR noise figure measurements. I have found just using the spectrum dBm measurements easier than the dBm meter. It usually reads -140 dBm constantly with low noise floors. 
Thanks,
Larry

On Jun 23, 2021, at 9:49 PM, jdow <jdow@...> wrote:

 That's a big subject.

To a first approximation the spectrum is very accurate for differences in reading. It's theoretically perfect if there is a perfect A/D converter involved. The A/D converter's step to step linearity can mess up this theoretically perfect relative calibration.

In any absolute sense any calibration present is rather loosy goosy unless you provide a precision source and take care getting your readings. Otherwise "loosy goosy" can mean +/- 20 dB or worse.

I refuse to address Simon's S-Meter accuracy until I check to see if I can still spoof it.

{^_^}

On 20210623 17:53:16, Larry Dodd wrote:
I have been asked the question, "How accurate are the SDR-Console dBm spectrograph and dBm meter readings?"  Can anyone answer that question? We are interested in measuring the noise floor of various SDR receivers.
Thanks,
Larry, K4LED


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