karlist July 8, 2019 at 6:41 am
- This topic was modified 1 week, 5 days ago by karlist.
Hi I am making this topic as a continuation to another topic from a while ago (https://signalhound.com/support/forums/topic/bb60c-emc-measurementshow-to-lower-the-noise-floor-of-my-setup/).
I made a new topic because I wanted to extensively describe our setup so professionals from Signal Hound might see where is(or isn’t?) the problem.
So, we we upgraded our chamber and now the setup is like this:
Antenna – 1m cable RG316 – 20 db amplifier – 3m Rg316 cable – RF / Coaxial Adapter – 5m cable – BB60C
Factor diagram parameters I entered in Spike software
20 dB amplifier TBWA2/20dB https://www.tekbox.com/product/tbwa2-wideband-rf-amplifiers/
3m Rg316 cable:
parametri no signal hound
• Damping 1GHz: 1,2dB (0,240dB/m)
• Damping 2GHz: 1,9dB (0,380dB/m)
• Damping 3GHz: 2,2dB (0,440dB/m)
• Damping 6GHz: 3,5dB (0,700dB/m)
EMC table parameters:
Radiation if there is no DUT in our chamber:
Radiation of DUT in horizontal polarization:
Radiation of DUT in vertical polarization:
Same DUT in certified lab :
Pictures of our chamber.
So our goal is to get measurements in our lab as close to measurements of certified lab.
As you can imagine, we have already invested a small fortune in our equipment so we are expecting a little bit better results than this.
Main issue is that I see 48 dBuV/m 180 Mhz peak in certified lab results but in our lab it is 70…
Regarding the low frequency noise – big reason for it is our noisy poe supply and our ethernet filter for chamber probably is not as good as for certified lab. Our filter: https://adauratech.com/anechoic-chamber-filters/specifications/
1. Is this radiation that BB60C is measuring in chamber without DUT “legit”? I have no previous experience in EMC measurement field, so it seems kinda wierd that we are not seeing
lower numbers…Can you please recheck the Path Loss table information shown above? Maybe it is just an error in these. I have checked them multiple times…
2. How can we increase the quality of our measurements? I guess we should add some more ferrite absorbers. Any tips where to put them? We do not have enough to cover all walls.
3. How far in to plywood box should we put the antenna?
4. How far from wall should the DUT be?
ANY advices would be really appriciated! This issue is becoming more and more exhausting..karlist July 8, 2019 at 10:36 pm
I failed with the image upload, so I will upload them as attachments in replies.
Kārlis TučsParticipantKārlis Tučs July 9, 2019 at 12:53 am
more images in attachment..I couldn’t add more image with original account..karlist July 9, 2019 at 3:12 am
4 last images
Justin CrooksModeratorJustin Crooks July 9, 2019 at 11:40 am
This is a difficult question to answer. My first question is, what antenna distance are you using? Is it the same distance in both cases (certified test and pre-compliance test)? If not, there is a 20 log (d2/d1) dB correction to apply.
Obviously your chamber is not anechoic, which will change results, and VSWR on your antenna and amplifier can change things. I can see these stacking to produce maybe a 6-8 dB variation, but 20 dB seems a bit excessive.
Do you have two of the antennas? If so, you could calibrate your system in position using a signal generator instead of your DUT…
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