Murata SWF accuracy and PCB layout question

Hi guys. I was observing the PCA10121 PCB layout using this link.

 Schematic for PCA10121 nRF5340 Audio DK 

From Murata SWF connector datasheet, it says

https://www.murata.com/-/media/webrenewal/support/library/catalog/products/connector/o30e.ashx?la=en-gb&cvid=20220210015534000000

Connector performance is influenced by GND among inner layers of substrate.

We recommend making space more than 0.4mm between connectors and GND.

In case of PCA10121, to follow Murata's 400um keepout rule, which layers are removed under J1 (MM8130-2600)? Is it

Dielectric 1 + Mid layer 1 + Dielectric 2 + Mid layer 2 = total 212um? OR

Dielectric 1 + Mid layer 1 + Dielectric 2 + Mid layer 2 + Dielectric 3 = total 1212um?

Also, under J1, the Top layer GND can be kept, right?

Lastly, SWF datasheet doesn't show the insertion loss after 6 GHz.

Is the SWF or SWG reliable when measuring 2nd, 3rd, 4th, ... harmonics? I know one Nordic Thread recommended UFL connectors

 SWF connector for customized PCB 

but I would like to use SWF due to the convenient feature of this connector so I'd like to hear your tips and what accuracy were observed.

Thank you so much!

  • Hi,

    Seems you have the latest version of the HW files for the Audio DK, but you can always find the files you need for our products on the product page download section. So adding the link to the download section here just as a reference for future: https://www.nordicsemi.com/Products/Development-hardware/nRF5340-Audio-DK/Download?lang=en#infotabs

    Dielectric 1 + Mid layer 1 + Dielectric 2 + Mid layer 2 + Dielectric 3 = total 1212um?

    this would be the correct way to measure the distance.1.212um. 



    Also, under J1, the Top layer GND can be kept, right?

    From the datasheet you can see that GND is directly under the connector on the top layer, so following the datasheet this can be kept.

    As for what impact it would have to not include the top layer GND i am not certain so this might be something that the manufacturer can answer better or if someone else has done any experiments with this that can comment in more extent.


    Is the SWF or SWG reliable when measuring 2nd, 3rd, 4th, ... harmonics? I know one Nordic Thread recommended UFL connectors

    From the simple testing i have done with SWF and adapter wire\connector and compared to the results form directly connecting a coaxial cable to the RF line when measuring the output from the radio there has not been any major differences two the harmonics as i can recall. There is some extra loss when using extra converters\adapters but that can be adjusted for.


    But if your are looking for third party antennas with the SWF connector that might be difficult so so then a UFL is more common and makes more sens to use. Think that is mostly feedback in the other ticket you referenced. As that customer wanted to use external antenna.


    Regards,
    Jonathan

  • Thank you so much Jonathan! One additional question before closing this please.

    I'm only using the SWF connector to measure the RF using the spectrum analyzer. No 3rd party antennas will be involved.

    From the SWF connector's datasheet, is says "DC to 6GHz". When you said

    "there has not been any major differences two the harmonics as i can recall."

    the 3rd (7200 MHz) and above harmonics are still readable, even though the datasheet says DC to 6GHz, right?

    May I ask the amount of "difference" you observed? Even a rough number is greatly appreciated!

    EX: Spectrum analyzer read -50 dBm at 7206 MHz and 9608 MHz when using the UFL (with RBW = 100 kHz etc)

    VS

    Spectrum analyzer read -49 dBm at 7206 MHz and 9608 MHz when using the SWF connector

     

    For me, this "DC to 6GHz" range was always got into my mind when measuring.

  • I don't have any concrete number, but i can do some test if that is of interest to you, i will only be able to compare SWF with coaxial probe, and not a UFL connector.  But using a UFL connector that is rated up to rated up to 12GHz or higher is probably the "correct" choice. But that is a bit more inconvenient as you would have t change the layout.

    Regards,
    Jonathan

  • Thank you Jonathan. No need to rush regarding the "compare SWF with coaxial probe" experiment.

    I can wait for your results. Greatly appreciate your time and investigation!

  • Hi,

    So did some quick tests just to see if there was much of a difference and provide some numbers. 

    Adding a power point with the plots, only for channel 40 with +4dBm. I did not adjust for the difference in loss with the two connection types, but a quick comparison between the delta variation of each "connector" seem to show that they perform about the same. Wit the setup we use when we do tuning on customer products. 


    SWF connecotr VS Coaxial probe.pptx


    The coaxial probe was connected to the same pad that the SWF connector is connected to, so physically on the PCB the connectors where on the same location. 


    So for testing and inspecting it is ok, but for official certification high accuracy measurements then I would go for a connector that is rated for the task specifically. 

    I can do some more if you have anything specific in mind. 

    Regards,
    Jonathan

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