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daniel59
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Why my bluetooth signal is bad?

Hi,

I use a a ceramic chip antenna, RFANT3216120A5T by Walsin, connect to DA14580 with a 6.8nH inductor and 50 ohm Impedance Transmission Line according to RFANT3216120A5T datasheet, and a 3.9nH inductor according to AN-B-018 section 3.7.

My board can only be detected in about 2 meters distance.

Is there anything I forget to place on the board?

Daniel

Device: 
MT_dialog
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Hi daniel59,

Hi daniel59,

The range of a device (antenna) depends on multiple factors, impedance matching, placement on the PCB, trace length, etc, even not proper soldering on a ceramic antenna on the PCB can cause range issues. You can have a look at the IoT reference design documents, the IoT uses a Ceramic Antenna and use this as a reference.

Thanks MT_dialog

daniel59
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Hi MT_dialog,

Hi MT_dialog,

I find the IoT project use a Pi matching, without the 3.9nH inductor. It's different from AN-B-018 section 3.7. Why?

Daniel

MT_dialog
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Hi daniel59,

Hi daniel59,

Because it uses a different antenna, the AN-B-018 document deals mostly with PCB antennas and not ceramic antennas. Apparently there was no need for additional matching on IoT and thats why they didn't place that inductor. I suppose that the improvement with the additional inductor was minor.

Thanks MT_dialog

daniel59
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Hi MT_dialog,

Hi MT_dialog,

I found the note on the antenna datasheet....it said "The antenna matching network values here are used when antenna is mounted on evaluation board"......

I think maybe this is my problem....

So how can I calculate the matching component for my board? Is there any online RF calculator recommanded?

Daniel

MT_dialog
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Hi daniel59,

Hi daniel59,

When knowing the antenna impedance (this should be measured in the full application with plastics using a network analyser), and knowing that the RFIO of the 580 is 50 Ohm, one can calculate the required values for a PI-network matching filter. After doing so you should repeat the measurement and the result should be close to 50 Ohm. You will be able to find a tool for determining the matching components parts in the following link http://www.fritz.dellsperger.net/smith.html.

Thanks MT_dialog

daniel59
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Hi MT_dialog,

Hi MT_dialog,

If I have antenna s-parameter file, like Johanson's antenna 2450AT07A0100, do I still need the network analyser? or I can pick one with 2.44Ghz frequency into the smith chart from .s1p file?

Daniel

MT_dialog
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Hi daniel59,

Hi daniel59,

Best is to measure the antenna impedance from output of matching network, without matching network and 580 connected. Remove e.g. a coupling capacitor for this. To be done in a full application, so including battery/covers/plastics. A S-par file can be made.

After having determined the matching filter network values, the impedance must be verified at the matching network input, without 580 being connected. All not so easy and RF experience is required.

If the board design around the antenna is very similar to that of the antenna supplier (used when creating the S-par file) and covers etc are relatively far away, you could try to simply use the S-par file provided by the antenna supplier. Please note to route a 50 Ohm track from 580 to the antenna/antenna matching network.

Thanks MT_dialog

daniel59
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Hi MT_dialog,

Hi MT_dialog,

I read something about antenna, but still have a question....

Is antenna impedance changing with different board? if it doesn't change, I route a 50 Ohm track from 580 to the antenna/antenna matching network, it can be matched all situation.

And Why it will change?

I asked Walsin, and they say the antanna impedence is 50 Ohm, so can I simply route a 50 Ohm track between antenna and 14580?

Daniel

daniel59
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Hi MT_dialog,

Hi MT_dialog,

So I still need VNA to ensure the best performance?

Daniel

MT_dialog
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Hi daniel,

Hi daniel,

Usually on SMD antennas a track at 50 Ohm is enough in order to achieve a good performance of the antenna, regarding the suroundings of the board and the PCB thats usually applied in printed antennas, but suroundings can also affect the performance of an SMD antenna (reflections from encliosure etc can affect the performance). So if you use the 50 Ohm SMD antenna and the track on your PCB is at 50 Ohm your device should be ok. If the device doesn't perform well if the above are applied and you still get a poor range, then you will have to start looking for alternate problems (2 meters is quite low for an antenna), so perhaps this is an assembly problem or could be an untrimmed XTAL16 or toggling one of the pins that causes crosstalk on the XTAL16 (P1_2 or P1_3) depending on your package. If you would like to achieve best performance of the antenna then this is something that requires an RF engineer.

Thanks MT_dialog

daniel59
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Hi MT_dialog,

Hi MT_dialog,

Thank you for your answer!

I will look for these problems.

And one more question, if I use the 50 Ohm SMD antenna, and the track on PCB is at 50 Ohm, if I place a shunt 3.9nH inductor according to AN-B-018 section 3.7, which says it will ensure best RF sensitivity and highest RF output power, will the antenna be dismatched?

Daniel

MT_dialog
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Hi daniel59,

Hi daniel59,

Well, the extra inductor is an additional matching component, if your antenna is allready matched as is, I assume that it will affect the performance of the antenna but not in large extend, i mean that it wont reduce the range of the antenna in a large value.

Thanks MT_dialog

daniel59
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Hi MT_dialog,

Hi MT_dialog,

I see, thank you!

Daniel