Electronics > Beginners
Replace 50 Ohm track with coax?
FriedMule:
Hi:-) Just a hopefully simple question about impedance.
Top board is the original and and have a track (yellow arrow) that demand 50 Ohm impedance
I plan on soldering a RG400 coaxial 50 Ohm cable at At X1.
Is it possible to remove the track (lover image) and just connect the RG400 coaxial directly to X1 there?
magic:
It certainly is possible and even likely to work ;)
That being said, that's not exactly the typical footprint for soldering coax onto PCB. See how it's done in WiFi gear:
https://openwrt.org/_detail/media/tplink/tl-wdr3600/tl-wdr3600_board-top-side-wlan.jpg?id=toh%3Atp-link%3Atl-wdr3600
Not sure what's the role of R8/R9. Some kind of 50Ω termination with built-in divider/filter?
radiolistener:
yes, if this line is 50 Ohm, then it's possible. But the solder point will be too close to R9 and if you will use inaccurate soldering with a lot of solder and a large tip of wire it may affect impedance. But it seems that this design is not intended for ultra high frequency, so the effect should not be significant and you can use both cases.
Also, make sure that this line is really 50 Ohm, because it may use different impedance. For example, this line may be used as impedance transformer, then it's impedance is not 50 Ohm and you cannot bypass it without disrupting the operation of the circuit.
FriedMule:
--- Quote from: magic on September 17, 2019, 06:19:15 am ---It certainly is possible and even likely to work ;)
That being said, that's not exactly the typical footprint for soldering coax onto PCB. See how it's done in WiFi gear:
https://openwrt.org/_detail/media/tplink/tl-wdr3600/tl-wdr3600_board-top-side-wlan.jpg?id=toh%3Atp-link%3Atl-wdr3600
Not sure what's the role of R8/R9. Some kind of 50Ω termination with built-in divider/filter?
--- End quote ---
You are right about the strange Coaxial footprint, did just select something in a hurry:-)
About R8/R9 Here is a part of the schematic.
FriedMule:
--- Quote from: radiolistener on September 17, 2019, 08:12:40 am ---yes, if this line is 50 Ohm, then it's possible. But the solder point will be too close to R9 and if you will use inaccurate soldering with a lot of solder and a large tip of wire it may affect impedance. But it seems that this design is not intended for ultra high frequency, so the effect should not be significant and you can use both cases.
Also, make sure that this line is really 50 Ohm, because it may use different impedance. For example, this line may be used as impedance transformer, then it's impedance is not 50 Ohm and you cannot bypass it without disrupting the operation of the circuit.
--- End quote ---
Sorry but I am not 100% sure I do understand all what you write, so please bare with me in my answer.
As I understand it, the track is meant to be 50 Ohm and the RG400 should be 50 Ohm. The circuit is meant to go from 0Hz to 1GHz.
Is there a way to look at the schematic to find out if the track is an impedance transformer?
New image shows what I think of using as solder pads, any comments about that?
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