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# Antenna test for phones using power meter

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#### tyne

##### Newbie level 6
Can anyone advice me on whether it is appropriate to use power meter to test for GSM phone antenna. The test is to ensure that the antenna is connected/soldered properly onto the pcb. It can be on any GSM band. It is feasibility to do it?

Thanks!!!

Maybe you can connect an antenna to a spectrum analyzer. Put relative close your mobile and try calling. The spectrum analyzer will show the power in dBm that the antenna receives.

The above method we used it in a lab at my university so I guess it's ok

GSM handsets adjust their transmitt power to use as little as possible to maintain communication. You may see a considerable variation in power output depending on if the phone connects to a far or near cell (near cell might be busy), wether someone is standing between the phone and the cell etc.

You may not be able to tell the difference between a phone with poor antenna connection trying to put out 2W and a phone with a good antenna at 1mW.

GSM phones transmitt in bursts so a typical signal strength meter won't give an accurate result. You would have to compare to a known-good phone.

An option is to use a Spectrum Analyzer, using Zero Span mode, video trigger, RBW = 1MHz, etc.

About your question, if is possible to use a power meter, the answer is yes, if the power meter allow you to trigger the GSM burst. Actually this method is more accurate than using a Spectrum Analyzer.

It is another empirical method to use a Power Meter without trigger:
-Set your Power meter on Average mode
-On your mobile use a standard GSM transmission (one TX burst)
-Duty cycle in this case is 1/8 = 0.125
-If you transmit full power in GSM900 (33dBm – PCL5), the Power Meter will read the average power: Pavg = 33*0.125 = 4.1dBm
-To find the real output power of your mobile (Peak Power), Ppk = Pavg*DutyCycle
-These are numbers for conducted power. For radiated power using the internal antenna, you have to subtract antenna gain and path loss. Make a reference and compare with it the other measurements, and in this way you will know if the internal antenna is properly connected.

Actually 1/8=0.125=-9 dB so the
measurement would be 33-9 = 24 dBm

This will be a radiated test. The phone will transmitt at PCL level 5.

How about using a coupler to pick up signal from the phone and then the signal will go through a RF to DC voltage convertor..and a DVM will be use to read.

Which will be a better method? Using a RF to DC voltage converter or using a power meter?

thanks

My mistake…Pavg = 2 Watts * 0.125 = 0.25W = 24dBm
But in principle for your application doesn’t matter what level of power you read on the meter, because you have to take in consideration path loss and antenna gain.
And anyway this would be a relative measurement. You have to compare each radio with a reference (a “golden radio”).
The best would be to use an RF Power Meter and a shielded box that have an internal antenna coupler, like this:

I think that if you deal with mass production or development you should have
Near-field system it will give you the all parameter you need and more.
It's expensive but it saves you time and money

Look at http://www.orbitfr.com/index.asp?ItemID=647

you should have java installed to see the page.

PL

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