Connect with us

GPS receiver board - can I remove the SMA connector?

Discussion in 'Radio and Wireless' started by loadlover, Jul 14, 2020.

Scroll to continue with content
  1. loadlover

    loadlover

    3
    0
    Jul 14, 2020
    Hi,

    Your best guess needed! This is a small u-blox GPS receiver board. Can I remove the SMA connector (I must save weight and size), and just use the U.FL connector? Will this have consequences for the RF circuit?

    Thanks!
    -- Anthony
     

    Attached Files:

  2. Martaine2005

    Martaine2005

    2,967
    817
    May 12, 2015
    You may find the SMA connector has a 50 Ohm impedence.
    If you remove it you will have to match the impedence.
    But I would measure it to see if it has or not. There might be a 50 Ohm resistor next to it on the board.

    Martin
     
  3. loadlover

    loadlover

    3
    0
    Jul 14, 2020
    Hi Martin,

    I'm sure it is 50 Ohm impedence. Would I need a signal generator and oscilloscope to measure this, or is there simpler way? And what would I replace it with that wouldn't weigh much?
     
  4. Martaine2005

    Martaine2005

    2,967
    817
    May 12, 2015
    A 50 Ohm resistor should be all that’s required.

    Martin
     
  5. Nanren888

    Nanren888

    339
    84
    Nov 8, 2015
    Sorry, I'm not sure what is meant here.
    The SMA is not terminated. So it appears as an open. The line to it and the SMA will appear as appropriate for a 50 Ohm characteristic impedance, but at the SMA, with no load plugged in, it's an abrupt open.
    If the board is intended to be run with the antenna on either connector without termination on the other, as I'd guess, then I'd guess removing the connector is likely fine.
    I'm not particularly an RF black arts guy, so happy to be corrected.
     
  6. loadlover

    loadlover

    3
    0
    Jul 14, 2020
    Yeah that's kinda what I was thinking. To clear one thing up, you're supposed to use one connector or the other, not both simultaneously. Bearing this in mind, what do we think?

    And yes, RF does seem to be a black art.
     
  7. Martaine2005

    Martaine2005

    2,967
    817
    May 12, 2015
    I am really not sure. I read that the connector has a 50 ohm impedence.
    Wiki.
    I know for audio, (older) a power resistor as a dummy load is used rather than the speaker while servicing.
    Likewise, not to transmit a radio without an antenna or dummy load.

    Martin
     
  8. Nanren888

    Nanren888

    339
    84
    Nov 8, 2015
    Didn't see a part number, but assuming this is a GPS or similar. The antenna is receive only.
    Somehow on the board they have arranged that you can plug a receiving GPS antenna into either connector and the other, open one isn't an issue. I'd presume this is mostly by just keeping the line short, though it feasibly could have two inputs to the module.
    Termination can be important? Absolutely: In RF even more so than audio. if transmitting or don't want reflections from open/shorted lines.
    Summary:
    Don't think we are in any transmitting situation, hence a lack of termination is not going to be an issue to the module safety.
    The "other" connector is normally open, so removing it, carefully so as to not mess with the board too much, is likely just shortening the line a little, shortening a rather short stub off the line being used: used antenna connector to module.
    Seems very likely to be ok.
    Disclaimers: Never looked at how these modules provide the two inputs. Not an RF guy (even less than previously).
    You could try asking UBlox.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-