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#bug_report #bug_report

 

Erik.
I noticed strange behavior on tinySA. After I added the 3 33pF capacitors the spectrum was free of the 48MHz spurious, but strangely, these spurious were helping, as they were forcing tinySA to start scanning the spectrum. Now, a signal above -70dBm is needed to start reading. that is, if I finish turning on tinySA and the signal I intend to read, it is between -71dBm to -80dBm -90dBm ... tinySA does not read until I force this reading by injecting -69dBm. It seems that there is a logic to start processing, only when the signal is greater than -70dBm. (it doesn't look very interesting.)
 

Set the start frequency to 1MHz to avoid the zero Hz peak that keeps the auto attenuator at 30dB
Or disable auto attenuation in the startup settings and set attenuation to zero

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For more info on the tinySA go to https://tinysa.org/wiki/
 

On Wed, Dec 16, 2020 at 04:45 AM, Erik Kaashoek wrote:
Set the start frequency to 1MHz to avoid the zero Hz peak that keeps the auto attenuator at 30dB
Or disable auto attenuation in the startup settings and set attenuation to zero

? In addition to the attenuation setting, the resolution bandwidth (RBW) of any spectrum analyzer also determines its noise floor (and how small a signal you can measure).? So if you need to measure signals in the -90dBm range then in addition to using 0dB attenuation you should also lower your RBW to at least 100kHz (Frequency->RBW->100kHz).

? Lower bandwidths increase your sweep time so unless you really need to scan the entire 350MHz span you should reduce your frequency range to the area you are interested in.? Examples follow using my tinySA with the same capacitors installed.


With 30dB attenuation and 600kHz RBW the? ? ? ? ? ? ?With 0dB attenuation and 600KHz RBW the noise? ? ? With 0dB attenuation and 10kHz RBW the noise
noise floor is ~-60dBm.? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?floor is ~-89dBm. No 48kHz signals detected.? ? ? ? ? ?floor is ~-100dBm.? Reduced 48KHz related signal detected.
????

Note in the above screenshots how the scan time for a 350MHz span increases from 405ms to 115.8s for a RBW change of 600kHz to 10kHz.? Professional grade spectrum analyzers also have increased sweep times with reduction in RBW, but are orders faster, and orders more expensive than the tinySA.

- Herb

tinysa_screen_6000kHz30dB.png

 

Perfect. The "problem" is only noticed if you don't make any adjustments and as I didn't have any presets defined, I didn't notice. But defining the limits: it starts at 88MHz and ends at 108MHz even without antenna you can already perceive an amplitude of -100dBm coming from local FM broadcasts. it's perfect. Thanks. In short (there is no problem and it works exactly as it should).
Thank you very much for your feedback.
Hug and peace.
NOTE: I would still like to see the external attenuator being added to the amplitude display values in the RF Generator mode. This would be very useful, as I use tinySA's RF generator a lot. But with a calculator on the side, everything is perfect.
 

Thanks for the demonstration and explanation.

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