[Nexus 7 General] bigbop:
pool0513 - continuity IS a measurement of resistance - just a very low resistance.

Since you don't understand radio frequency circuits, let me explain:

- you showed me a diagram of you measuring the wifi pins on your Nexus 7's motherboard.

- i provided the actual schematic of that output circuit for you.

- in that circuit, please note there are coils (inductors) that connect the RF output to ground.

- those coils at DC look like a short. A short is 0 ohms resistance, which causes your continuity meter to beep.

- at 2.4GHz however, the coils form part of an RF tuned circuit. At this point, although there is still a DC resistance, we are now working with AC Impedance (AC resistance, which your ohmmeter can't measure).

- This is a good document: http://www.ax84.com/static/rdh4/chapte23.pdf to read.

- so, at 2.4GHz, there is no 'short'.

-the 'characteristic impedance' of coax is not a DC resistance - it is the RF impedance between the shield and the center conductor over a wide range of RF frequencies. All you can measure with an ohmmeter is either the shield OR the center conductor continuity OR if there is a short between the two. A perfect piece of coax will have infinite resistance between the shield and center conductor.

- please note that the tuned circuit requires that all the properly designed components and the antenna must be properly matched in the output circuit in order to minimise signal reflections. Thse reflections are known as the VSWR, which must always be no more than 1 (for a perfect antenna to output match) but is typically around 1.25 to 1.5. A VSWR of 6 means 51% of the transmitter output power is being reflected back from the antenna - that is bad and can damage the transmit circuit over time.

Now, if you look at the internal wifi antenna on the inside of the Nexus 7 back cover, you will see that it appears where the two motherboard contacts connect to it, they short out. Again, this 'short' is an inductor and at 2.4GHz looks like a high resistance. What we have here is an Inverted F antenna, tuned to 2.4GHz for maximum power transfer from the RF output of the Nexus to the antenna.

The commercial antenna you're trying to use is most likely similar, but way bigger for increased gain.

In order to properly measure any RF circuit, you MUST use what is known as an RF Vector Network Analyser - one from HP will set you back around $60,000US.

To sum things up,

-when you want to modify any high frequency RF circuit properly, you cannot just solder another antenna to it.

You need to know the operating frequency of the antenna (in your case this ranges from 2.401GHz to 2.473GH. Any antenna you want to connect MUST be designed with its operating range optimised for this band and centred on 2.437GHz. If the antenna is not designed for this, your VSWR will be high, resulting in a reflection of radio energy back to the transmitter output.

-you need to solder the coax to the radio output using very short connections (where the centre conductor comes out from the shield) as ANY type of connection will always alter the impedance matching in some way. BoomBoomChuck found this out if you read his original posts and he had to try a few times to connect his coax just right on the motherboard.

-with RF, you need to keep wiring very neat and make sure the coax does not get pinched anywhere.

Finally, you can't determine if an RF circuit is good or bad by just using a simple ohmmeter.

I hope this helps.