USB WiFi Antenna Mod

I am working on adding a helical antenna to a cheap USB WiFi adapter.  My question is where do I connect the antenna to existing circuit.  I've attached a closeup picture with three likely points.  My three main questions are:

1) Where to connect the external antenna

2) Do I disconnect the rest of the onboard antenna (my gut says yes) or just add in the new

3) What impedance will the external antenna need to match?  I assume the components between points C&B and B&A are for some kind of impedance matching.

Picture of USB WiFi Antenna Mod
WiFi Dongle Info.jpg
WiFi Dongle PC Board - Possible Locations.jpg
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That position at B IS for a surface mounted connector, A is definitely an impedance matching network for the antenna, so that the SWR is acceptable. Gotta guess at 50 Ohms.

Steve
telfon (author)  steveastrouk4 years ago
Thanks Steve. That sounds right. I'll connect the external antenna at B and I can even connect the shield there since it looks like they left that part of the ground-plane uncovered. I'll cut the rest of the antenna network at A out and try to match a 50 impedance.

I bought 5 of these cheap USB adapters online a couple of years ago when they were on sale for $5 or something. If this first one works out I'll right up a nice Instructable converting a couple of other ones.

-- Paul
I'm not sure about the impedance bit but it looks like you could easily test it by scraping off a little coating on the PCB touching your antenna leads on, as long as you didn't short anything else I don't see anything too disastrous happening. I tried a few experiments like that with my dongle then put it back together when I needed it... No harm done...

My experiments failed, probably because I have a habit of just slapping things together to see if they work...
The only thing dangerous is putting your dongle where it's not supposed to be.
you are right caitlinsdad. I agree with you
In my defence I totally thought it'd get better reception there...

The doctor believed me, he even raised his eyebrow in belief...
Not what she said.
Her idea...