4 ms·

That's explained in the comments on the original source. It turns out that the curved bit of trace is significant: if you leave it connected but unterminated i

That's explained in the comments on the original source. It turns out that the curved bit of trace is significant: if you leave it connected but unterminated it'll be resonant near the 5th harmonic of the wifi signal, which is bad. Microwave RF is hard.

regularfry 5y ago
Oh, also it's a capacitor, not a resistor. I don't think that changes the explanation, though.
- jacquesm 5y ago
  On the contrary, that makes all the difference: it's an LC circuit that is resonant at a frequency that you don't intend to amplify.
  - regularfry 5y ago
    It is, but if the proposal is to desolder the component from the board, does it matter which it was?
myself248 5y ago
By the time you get to that high a harmonic, the signal is way, way, way down. I have to imagine these footprints, both the u.fl footprint and the 0402 footprint, were meant to be used during testing, and I can't imagine that their own testing also involved Dremeling off a trace. Removing the cap at the end of the curved stub is surely fine.
- regularfry 5y ago
  Good point about the testing. I guess it's cheap and easy enough to try out, right?
  - buescher 5y ago
    If you trust your test setup for 17.4 GHz to be within a few dB of what you'd get at a certified test lab, sure. Yeah leaving the stub is bad practice because it could cause you trouble in FCC certification, not because it always will or even probably would. Let's put it this way, if you wanted to get enough energy into your fifth harmonic to be within 10 dB of what you were putting out on the fundamental by leaving a stub like that... you would tear your hair out for a good long while before giving up.
  - myself248 5y ago
    Nothing about testing at those frequencies is cheap, and very little of it is easy, but it's certainly doable for someone who already has the lab.
    - regularfry 5y ago
      It's simpler than that, though - if you're pushing energy into the 17GHz band, that's energy which is not going into 2.4GHz. If the curved trace is significant, leaving it on should raise the noise floor and lower the signal level of the wifi signal we care about. That should be observable in the performance of wifi itself. You don't need to directly measure it unless you care about the FCC.
      - myself248 5y ago
        Logarithmic scales are devilish things, though. Spurious emissions have to be at least 20dB down from the carrier, which means a factor of 100. And I'm highly skeptical that you can measure a 1% difference in wifi signal strength by looking at something like performance alone, given all the counfounding factors.

regularfry 5y ago

Oh, also it's a capacitor, not a resistor. I don't think that changes the explanation, though.

jacquesm 5y ago
On the contrary, that makes all the difference: it's an LC circuit that is resonant at a frequency that you don't intend to amplify.
- regularfry 5y ago
  It is, but if the proposal is to desolder the component from the board, does it matter which it was?

myself248 5y ago

By the time you get to that high a harmonic, the signal is way, way, way down. I have to imagine these footprints, both the u.fl footprint and the 0402 footprint, were meant to be used during testing, and I can't imagine that their own testing also involved Dremeling off a trace. Removing the cap at the end of the curved stub is surely fine.

regularfry 5y ago
Good point about the testing. I guess it's cheap and easy enough to try out, right?
- buescher 5y ago
  If you trust your test setup for 17.4 GHz to be within a few dB of what you'd get at a certified test lab, sure. Yeah leaving the stub is bad practice because it could cause you trouble in FCC certification, not because it always will or even probably would. Let's put it this way, if you wanted to get enough energy into your fifth harmonic to be within 10 dB of what you were putting out on the fundamental by leaving a stub like that... you would tear your hair out for a good long while before giving up.
- myself248 5y ago
  Nothing about testing at those frequencies is cheap, and very little of it is easy, but it's certainly doable for someone who already has the lab.
  - regularfry 5y ago
    It's simpler than that, though - if you're pushing energy into the 17GHz band, that's energy which is not going into 2.4GHz. If the curved trace is significant, leaving it on should raise the noise floor and lower the signal level of the wifi signal we care about. That should be observable in the performance of wifi itself. You don't need to directly measure it unless you care about the FCC.
    - myself248 5y ago
      Logarithmic scales are devilish things, though. Spurious emissions have to be at least 20dB down from the carrier, which means a factor of 100. And I'm highly skeptical that you can measure a 1% difference in wifi signal strength by looking at something like performance alone, given all the counfounding factors.