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SA bandwidth for precompliance testing

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TK:

--- Quote from: nctnico on July 09, 2018, 07:20:02 am ---Just know that a spectrum analyser and a VNA are designed and optimised for different purposes. A VNA is typically worse at doing spectrum analysis compared to a spectrum analyser.

--- End quote ---
You are right, but there is a market for SA with VNA capabilities, like the JDSU (ex GenComm) 754A, Anritsu MS2711D, Keysight handheld SA, etc.  Maybe they are more Antenna and Cable Fault analyzers and not true VNA, but for the HAM Radio market, the combined function is very useful.

Smokey:

--- Quote from: tautech on July 08, 2018, 11:37:42 pm ---...

--- Quote ---....I am not sure if any vector network analysis is required for pre-compliance EMI testing.
--- End quote ---
Correct, there's no VNA requirement for EMI work unless you're wanting to build and tune your own EMI antennae so for this the new SVA could be very useful.

--- End quote ---
(Sorry, I know it's an old thread... )

What about tuning antenna matching network components on a PCB for the DUT?  Having a matching network that is way out of whack could cause issues during testing.  Need a VNA to sort that out.

tautech:

--- Quote from: Smokey on February 10, 2023, 01:04:08 am ---
--- Quote from: tautech on July 08, 2018, 11:37:42 pm ---...

--- Quote ---....I am not sure if any vector network analysis is required for pre-compliance EMI testing.
--- End quote ---
Correct, there's no VNA requirement for EMI work unless you're wanting to build and tune your own EMI antennae so for this the new SVA could be very useful.

--- End quote ---
(Sorry, I know it's an old thread... )

What about tuning antenna matching network components on a PCB for the DUT?  Having a matching network that is way out of whack could cause issues during testing.  Need a VNA to sort that out.

--- End quote ---
No worries.
Your only issue is connection and calibration at that point. If it's a experimental design you might use a SMA PCB edge connector and do the Cal just before it.
For that reason we chose a F603FE Female Cal kit so to be able to do a Cal at the end of our test cables so to get as near as possible to the DUT. Small stuff you might use a male PCB edge connector so to fit directly to the port adapter however you will find some antennae particularly susceptible to proximity effects so it's better to have them in free air rather than hard against an instrument.

Smokey:
I hacked some u.FL connectors into my last design for testing.

For my next designs that have chip antennas, I'm planning on putting unpopulated u.FL connectors footprints at both ends of the transmission line on the PCB (at source, and after the matching network right before the the antenna).  That way I can hook the VNA up without the source and match the antenna, and also have a connection at the other end with the antenna removed for direct testing.  u.FL signal and ground pads pretty much line up with the 50ohm microstrip trace.

pdenisowski:

--- Quote from: jmw on July 08, 2018, 06:53:28 am ---If I'm interested in EMC precompliance testing (with both conducted and near-field probing), are the lower-specced analyzers around 1.5 Ghz capable for the job or is more range needed? Let's say I'm mostly interested in looking at power supplies, which usually switch in the 100s of kHz - 1s of Mhz range.

--- End quote ---

I just presented a module two days ago on EMC precompliance at our Demystifying EMC conference :)  I think it will be available on-demand at some point, and I'm planing on turning it into a YouTube video / whitepaper shortly thereafter as well.

In the meantime, my short answer would be that 1.5 GHz is probably fine for SMPS precompliance, for both conducted and radiated emissions.

Perhaps more important than upper frequency limit are the noise of analyzer and a good set of near field probes (and potentially a preamplifier, if analyzer noise is high or probe quality is low).  A noisy instrument and/or low quality probes (or poor probing technique) are common issues in precompliance testing.

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