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Analog Angle

What Does Your Noise Nemesis Look Like?

Bill Schweber
Bill_Jaffa
Bill_Jaffa
8/12/2014 8:15:34 AM
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Re: Noise Temperature and G/T
I am always amazed at how engineers are able to design and build systems which can extract useful signals even when the SNR is so low and the RSS is also so low--think GPS, Sirius XM, and others--especially when the antenna takes on odd angles, and can't be steeredin any way. Totally unappreciated by the public, of course.

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eafpres1
eafpres1
8/12/2014 12:19:50 AM
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Noise Temperature and G/T
Hi Bill--nice article as always.  In my previous experience I worked with GPS antennas integrated to Low Noise Amplifiers (LNAs).  The physical antennas were usually metallized patch antennas on a high Dk ceramic puck.  They were high Q and had very narrow bandwidth, but that is OK for GPS.  The amplifiers were often 30 dB or even higher.  Typical in an OEM specification for sourcing such a module you find some figure related to noise, such as noise figure or G/T. The latter is the system gain divided by the aystem noise temperature.  Thie noise temperature includes the LNA.  Since the signals you are trying to receive from GPS satellites is -130 dB or lower, noise is a big worry.  So modules with really good amplifiers or high G/T were specified.

When I started in this area we were making GPS + Cellular antennas for telematics applications.  Amplifiers were 25 dB with a nosie figure of 1 or 1.2 dB.  Now, gains of 35 dB are common with noise figures of 0.5 dB or even better.  Tht represents a large improvement for an off-the shelf, nearly commodity LNA.

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