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The upper part of the signal goes up when I activate the lna

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The lna is supposed to be activated to see more of the lower part of the signal, but in my case, apart from seeing more of the lower part of the signal, the upper part goes up 3 or 4 db, so I don't know what the true value is. The signals I'm measuring have values ??between -70 and -60 dbm. What am I doing wrong?
 

I assume you did do a level calibration as described in the wiki under first use?
If yes, at what frequency are you looking
--
Designer of the tinySA
For more info go to

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Level calibration is done
 

Some go up, others not.
Are all signals constant level?
Is this also happening at other frequencies?
Otherwise no clue what is happening
--
Designer of the tinySA
For more info go to

 

Can you provide the antenna connection and the product label on the back of the tinySA so we can confirm the signal path and hardware version.
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The signals are stable, coming from a UHF antenna, in the FM zone the upper part coincides with lna and without lna.
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The antenna is connected to a UHF antenna, before the tinySA4 there are several attenuators so that the lna does not saturate. The noise level of the device is the red trace. The low part of the signal amplified by the lna looks really spectacular. The label is worn and practically nothing can be seen. The internal data of the device are
sw tinySA4_v1.4-7-gbd4f5a2 HW Version:V0.4.5.1 (167)
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These are probably digital signals. For a true comparison you have to use TRACE/CALC/MAX HOLD for a minute of so.
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This is what I get
Yellow is no LNA
Green is with LNA
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And even with maxhold for a minute there is still a difference
--
Designer of the tinySA
For more info go to

 

I had to try this too! I have an external 10db attenuator attached between the supplied antenna and the SA. EXT. GAIN also set to -10db so you are seeing the actual power received. Frequency span is 87MHz to 109MHz, basically the U.S. commercial FM broadcast band. Traces averaged, CALC16. Yellow is LNA off, red LNA on.
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The peaks are exactly where they should be though there are a number of stations that show up with LNA on but hidden in the noise when it is off
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I have detected that for signals with a higher level the LNA appears to amplify a little more and for lower signals it seems to amplify a little less. Rather, it seems that tinySA makes weak signals more visible when they are close to the noise level, recovering their real level when the LNA is on because the noise floor has moved away.
Yellow trace the DTT broadcast signal.
Green trace with LNA activated.
The other traces are the respective noise floors.
The respective graphs, the same DTD broadcast signal (WB 8MHz) attenuated by 0, 10, 20, 30, 40 and 50 dB at the input.
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It is pleasantly impressive to see signals emerge from the noise when the LNA is activated?
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Thanks Toni.
The 3 dB level difference when the noise and signal are almost equal makes sense because the noise and the signal add and create a factor 2 (3 dB) more power
The small difference with strong signals is unfortunate and there is not much I can do to correct it
--
Designer of the tinySA
For more info go to

 

Your signals are modulated.? Please pick unmodulated signals to run your tests.

Dave - W?LEV


On Sat, Nov 23, 2024 at 4:57?PM Toni Ciscar via <aciscar=[email protected]> wrote:
I have detected that for signals with a higher level the LNA appears to amplify a little more and for lower signals it seems to amplify a little less. Rather, it seems that tinySA makes weak signals more visible when they are close to the noise level, recovering their real level when the LNA is on because the noise floor has moved away.
Yellow trace the DTT broadcast signal.
Green trace with LNA activated.
The other traces are the respective noise floors.
The respective graphs, the same DTD broadcast signal (WB 8MHz) attenuated by 0, 10, 20, 30, 40 and 50 dB at the input.
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It is pleasantly impressive to see signals emerge from the noise when the LNA is activated?
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--
Dave - W?LEV
 

It is true, by doing the tests with a clean carrier, the difference with and without LNA is minimal, even at higher levels where it is not necessary to use the LNA. Thank you Dave and Erik.
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Toni
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In the FMM zone, the difference between the LNA on and off is not noticeable. In the zone around 500MHz, I get between 0 and 2,5 dB of difference. From a practical point of view, when the LNA is activated, it is to see what is below the noise level. If anyone wants to know the real value of the signal, they only have to look at the trace without the LNA.
 

Does the difference go up with frequency? I wonder if this might be related to the speed of the SA's clock chip??
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How do you know that the signal power with LNA off is the "real value" and not vice versa? You would need a very precise signal.
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I also seem to remember Erik once saying the SA's precision was about 2-3dBm...?

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