Can someone please confirm my theory about the reason of bad measurements?
Is antenna the issue here?

thanks in advance

Yes, antenna distance is same in both cases – 3 meters.
I just added some more ferrite tiles to chamber which decreased the spike at 179 Mhz by few dBs.

Do I understand correctly – because of my antenna which is very lossy up until 250 MHz, I wont be able to measure anything less than about 40 dBuV/m right at low frequencies?
As you can see in one of the images, when no device is in the chamber the radiation levels are shown as pretty high, and that happens because of Antenna Factor path loss table. At 30 Mhz it is 39 dB..

I have concluded I will not be able to somewhat precise measurements in frequencies below 250 MHz with this antenna..too bad..

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I just compared results between with/without attenuator.
I added a 20dB attenuator infront of BB60C.
I also added a 20dB offset in Spike software because of this attenuator.

Graph is almost the same, but now I have increased noise floor, so SNR is worse. From what you wrote I understand that this is sensitivity issue and an amplifier might fix this.

Also it seems that increasing the Max Input parameter increases the noise floor. I have to increase it because otherwise I get the IF overload warning. I hope amplifier wont make this worse.

Something is off with the replies in this forum. I edited my reply and it got deleted..

Thanks to both of you for replies!

Reply to Justin Crooks:
is the antenna the same distance as in your test site, or did you compensate readings for distance to DUT?
Antenna is 3m away from DUT in both cases – certified test lab and our lab.

Did you factor in any preamplifiers or cables used?
We do not use external preamplifiers so we did not have to factor them in. Regarding cables- yes, we added cable path loss table.

But can you tell why the noise floor is so high? And what result should we even expect in empty chamber? 30dbuV/m seems a lot.

Reply to kaiser:
So if I understand correctly you advise us to add a LNA to our setup right?
Can you give me one example of cheap LNA? I only found this one and it does not seem cheap to me :
https://www.aaronia-shop.com/products/breitband-vorverstaerker/hf-preamps/bypass-amplifier

I will do the test you described about ref level change and SNR.

Yes, I know we do not have anechoic chamber, we are gradually upgrading our chamber, but it should not affect the measurement if we are measuring empty chamber. We were surprised that we had 30dbuv/m noise floor in empty chamber.

BTW, we can even see the standing waves if we move the antenna 😀

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