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How to Measure Active Antenna Bias Voltage from GPS Receiver - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

 Post subject: How to Measure Active Antenna'bias voltage from GPS receiver
Posted: Thu Apr 19, 2012 12:32 pm 

Joined: Thu Apr 19, 2012 10:44 am
Posts: 2
Dear all,

A dummy question.
I've got a GPS receiver chip. This chip has a [+3,+5]VDC voltage bias for active antenna.

I wonder if it is possible to measure the presence of the voltage bias on RF port ?
The aim is to validate that the voltage is compliant with the LNA inside my active Antenna.

Basically, I though to directly connect the voltmeter on the central conductor of SMA port. Is it good ? Or is there a problem of mismatch ?

Best regards and thank you by advance.

Kirt Blattenberger
 Post subject: Re: How to Measure Active Antenna'bias voltage from GPS rece
Posted: Fri Apr 20, 2012 7:49 am 
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Joined: Sun Aug 03, 2003 2:02 pm
Posts: 476
Location: Erie, PA
Greetings florent:

The receiver input is almost certainly tolerant of any RF impedance as long as you are not worried about RF performance during the measurement, which you are not. If you can find the datasheet for the GPS IC, it will probably contain a warning about shorting the Rx input if it is a problem. The DC impedance of any modern DMM is extremely high (>1 MOhm), so you should have no problem making the voltage measurement. If you are still leery of placing the probe on the input, wrap the lead around your finger a few times to add a little inductance to the probe line as an RF choke.

- Kirt Blattenberger :smt024
RF Cafe Progenitor & Webmaster

 Post subject: Re: How to Measure Active Antenna'bias voltage from GPS rece
Posted: Mon Apr 23, 2012 7:14 am 

Joined: Thu Apr 19, 2012 10:44 am
Posts: 2
Dear Kirt,

Thank you very much for your answer.

I've performed the DC measurement : 3,25VDC which is the order of magnitude that I saw on various datasheet.
In fact, I haven't the reference of the receiver. Let me explain : I'm working on an analysis concerning GPS signal default. The GPS receiver chip is included inside an embedded computer. I've contacted the manufacturer to get the name of the GPS receiver but without succeed.
That is the reason why, I would just perform a first check of the DC bias voltage. I hope to get the datasheet from the manufacturer.

In all case, I thank you again for your support.
Your forum and web site is a great source for young dummy engineer like me.

Best regards,

Posted  11/12/2012

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