X4R - repairing the antennas

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interestingfellow
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Joined: Tue Jun 16, 2015 2:05 am
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Location: durham, nc

X4R - repairing the antennas

Post by interestingfellow » Mon Jan 13, 2020 12:30 am

TLDR Why is there a 120ohm resistor (are they resistors?) connecting ground and active on the u.fl connectors on X4R receivers? (as seen on left most x4r highlighted by green boxes)

I recently acquired 4 x4r from someone, 3rd hand. They were covered in conformal coating, which I removed *painfully slowly* with rubbing alcohol.

2 of them just need to be powered up and tested (I just did, they seem good!), the other 2...eh. The u.fl connectors have been removed one way or another; the pads are still there and good. But 1 of them has has L5 and L6 removed (middle pic, highlighted yellow) and the other doesn't have a spot for L5 and L6 but someone has hacked them into the traces to the u.fl connectors (right hand x4r, red highlight). Are those resistors? They are too small for me to see even with a magnifying glass, and my DMM says 123ohms each. I understand enough to know that they have to do with impedance or inductance or something. I'm plato's pig over here: not smart enough to know, but smart enough to know that I don't know.

Should I add 120ohm resistors to the x4rs missing them?
My plan is to use the 2 iffy x4r's for foamys and the 2 good ones for heli's, so they won't be used in anything dangerous or expensive.
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interestingfellow
Posts: 205
Joined: Tue Jun 16, 2015 2:05 am
Country: United States
Location: durham, nc

Re: X4R - repairing the antennas

Post by interestingfellow » Mon Jan 13, 2020 1:01 am

Someone has told me that they are 0402, the value 18 nH inductors

PeterB
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Re: X4R - repairing the antennas

Post by PeterB » Wed Jan 15, 2020 6:48 pm

Hi interestingfellow,
Yes the L component prefix signifies an Inductor, so a 0402 SMD package size 18nH inductor would seem reasonable & will probably be part of antenna tuning arrangement.
Personally, I wouldn’t mess with it unless you know what you are doing & more than happy to risk a model.


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