Can this Antena cause the nRF51 chips to burn?

RE: Can this Antena cause the nRF51 chips to burn?

bjorn-spockeli — Tue, 01 Aug 2017 06:31:24 GMT

I agree with @rogerclark, the inverted F antenna is harder to get right compared to the simpler quarter length antenna used on our nRF 5x DKs.

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Tue, 01 Aug 2017 05:45:15 GMT

Any reason you didnt just use the Nordic reference design ?

Antenna design is non trivial, and at these frequencies, tiny differences in track width or length or spacing make a big difference to the antenna performance

RE: Can this Antena cause the nRF51 chips to burn?

myjtag — Tue, 01 Aug 2017 05:30:21 GMT

Thanks, I have used the TI app note for their 2.4GHz antenna, also I have seen this design on a kick starter campaign containing the nRF51 parts, so I just give it a go! the design is an F inverted antenna and the feed line of antenna comes from C8 and since antenna has two ends, one of them should be grounded.

The TI app note is this swru120b

RE: Can this Antena cause the nRF51 chips to burn?

peterz — Mon, 31 Jul 2017 10:00:33 GMT

(not knowing how an F-Antenna is supposed to work...) if you can afford to sacrifice a PCB: remove the antenna with a cutter and solder a coaxial cable with a known, good antenna. Is the power consumption now as expected?

RE: Can this Antena cause the nRF51 chips to burn?

bjorn-spockeli — Mon, 31 Jul 2017 09:06:29 GMT

@myjtag: It is possible to use an inverted F design, but we generally recommend following our reference designs, i.e. using either quarter wave antenna or a meander antenna. Its hard to say what might be the issue without seeing the entire layout , but 200mA sound very very high. Could you upload the gerbers?

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Mon, 31 Jul 2017 06:35:06 GMT

OK. Depending on the type of antenna, I agree it could be connected to GND. and not be a electrical short to gnd.

But perhaps the autorouter PCB package decided to directly connect it to GND.

I would have thought, best practice would be to show the antenna as an inductor to GND if thats what is physically required, and then create a PCB symbol which is the physical shape of this inductor

This would get rid of the DRC errors without accidental shorting both ends of C8 directly to GND

RE: Can this Antena cause the nRF51 chips to burn?

RK — Mon, 31 Jul 2017 06:26:15 GMT

Not if, as research indicates, the stub end of the F antenna is meant to be grounded. Still don't know how that works but it appears to be correct.

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Mon, 31 Jul 2017 06:17:51 GMT

Ah... That would be a problem !

RE: Can this Antena cause the nRF51 chips to burn?

RK — Mon, 31 Jul 2017 06:02:50 GMT

I think that's what he meant yes.

RE: Can this Antena cause the nRF51 chips to burn?

RK — Mon, 31 Jul 2017 06:01:40 GMT

Is that the actual schematic? Because that schematic would have DRC errors because your layout bypasses C8. Or are you saying your schematic is like this except you have added a connection to ground in order to form the F antenna?

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Mon, 31 Jul 2017 05:59:20 GMT

Sorry. I can't post images as comments, So I'm trying to upload an image as an answer

but is this what you did ??

(See line in red at the end of the antenna to GND)

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Mon, 31 Jul 2017 05:53:55 GMT

Are you, really, saying that the node in the schematic labelled ANT is connected to GND ????

See my answer below, as I can't seem to upload images to comments

RE: Can this Antena cause the nRF51 chips to burn?

myjtag — Mon, 31 Jul 2017 05:42:30 GMT

Thanks, the schematics is regular with Nordic, the antenna is connected to it, and only one end of antenna is grounded

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Sun, 30 Jul 2017 23:17:31 GMT

AFIK, a quarter wave distance away from a short is open circuit, so its possible that this is correct.

However if the length is not quite a quarter wave, it will exhibit some lower impedance than a open circuit. Quiet what impedance is hard to calculate.

(Also the term "length" depends on a load of factors and not just the length of the track on the PCB)

RE: Can this Antena cause the nRF51 chips to burn?

RK — Sun, 30 Jul 2017 22:57:24 GMT

so I looked up inverted F antennae and indeed they are supposed to be grounded at one end. I don't think I'm ever going to understand how antennae work, not ever. We need abystomalabs or someone from Nordic who understands this stuff.

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Sun, 30 Jul 2017 10:20:33 GMT

@RK

Yes. It does look like either its connected to GND or supply.

RE: Can this Antena cause the nRF51 chips to burn?

RK — Sun, 30 Jul 2017 08:43:25 GMT

that would help - however just looking at that antenna it seems one end of it is grounded, so I don't see how it's supposed to work at all.

@myjtag where did you find that antenna design

RE: Can this Antena cause the nRF51 chips to burn?

Roger Clark — Sun, 30 Jul 2017 08:39:40 GMT

Post the schematic not just a picture of the PCB