Preselection filters

Hi guys,

Any recommendations for how best to implement a swept/switched preselection filter to turn my SA44B into something closer to an EMC receiver?
I found Hittite/Analog Devices’ MMIC tunable filter parts but they are outside the frequencies of interest, and also, by and large, obsolete.

I was thinking running a tunable LPF with a tunable HPF so I could create a variable BPF, or, because this is looking like a right pain in the backside, making a bunch of BPFs and switching them, and components in them, to cover the standard CISPR22 EMC range.

Or does someone have a better approach??

Jared

I would probably start with a BB60C for EMC it already has >50 dB spurious rejection, which is plenty for precompliance testing of unintentional radiators. For intentional radiators, I might just buy a simple high pass filter for looking at harmonics, and a low pass filter for looking at frequencies below the transmit frequency.

Preselection is a pain, and expensive, but when you need it there really is no good substitute. External high pass and low pass filters e.g. from Mini-Circuits, will work for many applications, but they do require manual setup.

Hi Justin,
Thanks for the reply.
I was looking at making a 250kHz wide adjustable BPF but that is way too tricksie. And making a switched version doesnt help, requires a massive number of filters…

So I’m just looking at breaking it up into the standard CISPR22 intervals with selectable HPF and LPF sections.

I looked at mini-circuits but that approach is going to add up pretty quickly.
I’d love a BB60C, however I cannot justify it for a personal purchase as it is compounded by the requirement for a new laptop too (to get USB3).
The office has shelled out for a NI VST but this is currently used in the factory for 3G radio compliance validation.

As I pretty much stick to working in specific bands (450-470), (928-960), (3.5-3.8) I use HPF/LPF filters in combination. I can benchmark the combined filters in to a BPF with a tracking generator. Normally I just leave the combinations alone and string-tag the assembly so I can pull things off the shelf and have a reproducible result.

I would love to have a super-adjustable BPF but the cost would be almost as much as the BB60C.

Thank goodness I am out of the compliance testing world and just do product evaluations and comparisons.

Yes that’s been the plan to date.
Though I saw the recent announcement of EMC/EMI precompliance support in Spike for the BB60C…
Looks great from the screen shot!! Well done to all involved!

Any plans to roll this into the SA44B?
Soon?
Pretty please!!

Because of the architecture limitations of the SA44B, it really is not a good fit for EMI precompliance. The SA44B is not capable of picking up some types of transient signals without disabling image rejection, and for EMC precompliance, you want a high degree of confidence for all types of signals that the SA-series really can’t provide.

So the EMI precompliance module in Spike will functionally work with the SA44B? You’ve just assessed that it doesn’t have the same degree of confidence so have disabled it?

Can you not enable the module for SA44B, but when the user clicks on it, bring up a disclaimer dialog? Or could you not rename the feature for SA44B users to “EMC/EMI pre-screening”? Or both?

I, and I’m sure others, would use the feature if it was available for the SA44B, even with the caveats.

The software module (tables/markers) would just make it easier to document potential areas to look at. Log freq scale make it match to the compliance lab outputs, etc.

When I did pre-compliance testing on our product, I reduced the span to smaller chunks and left it sweeping with average and max hold on…
I then wrote down all the peaks I thought were problematic, and then drilled down and, in real time analyser mode, looked at the areas of concern.

Can this happen? i.e. enabling precompliance for SA44B with a disclaimer?

Please.

Hi Jared,

At this point and time we do not have plans to implement this. I have made a note of your request as it may be something we decide to pursue in the future.

Regards,
A.J.

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