[time-nuts] Homemade GPS Receiver

Azelio Boriani azelio.boriani at gmail.com
Fri Sep 26 08:52:52 EDT 2014

>From gpsinformation.net:

In the frequency allocation filing the L1 C/A power is listed as 25.6
Watts.  The Antenna gain is listed at 13 dBi.  Thus, based on the
frequency allocation  filing, the power would be about 500 Watts (27

Now, the free space path loss from 21000 km is about 182 dB.  Take the
500 Watts (27 dBW) and subtract the free space path loss (27 - 182)
and you get  -155 dBW. The end of life spec is -160 dBW, which leaves
a 5 dB margin.

And if you really get into it, you'll discover ALL of the following
represent the same approximate signal strength for GPS on the face of
the earth (m stands for milliwatts and m2 stands for meters squared):

-160 dBW, -130 dBm, -135 dBW/m2, -105 dBm/m2, -223 dBW/Hz, -163
dBW/MHz, -193 dBm/Hz, -198 dBW/m2/Hz, -138 dBW/m2/MHz

On Fri, Sep 26, 2014 at 1:22 PM, Andrea Baldoni <erm1eaae7 at ermione.com> wrote:
> On Fri, Sep 26, 2014 at 10:07:56AM +0100, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
>> I don't understand the units of signal strength
>> "The L1 carrier is spread over a 2 MHz bandwidth and its strength at the
>> Earth's surface is -130 dBm. Thermal noise power in the same bandwidth is
>> -111 dBm"
>> Then goes on to talk about the signal being 20 dB below the noise.
> Hello David.
> It could be because there is a "process gain" associated in demodulating a
> spread spectrum signal.
> Best regards,
> Andrea Baldoni
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