GPS25 Antenna Amplifier 

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General Description

Signals from GPS satellites are very low in amplitude, often below –130 dBm (70 nV).  Usually an active antenna is used to boost these very low levels.  The active antenna is usually powered from the GPS receiver with DC being fed up the inner connector of the coaxial cable.

This arrangement works well as long as the cable from the active antenna is kept relatively short, e.g. less than 10 meters.  If the GPS receiver is more than 10 meters away from a view of the sky, the above arrangement may not work satisfactory.

The GPS25 inline antenna amplifier has been designed to overcome such problems.  The GPS25 is simply connected in series with the active antenna, as near the antenna as possible.  DC from the GPS receiver now powers the GPS25 as well as power still being fed to the active antenna.  Thus no extra power supply is needed for the GPS25.

The GPS25 can be ordered with gains of 10 dB to 35 dB.  Therefore extra lengths of cable can now be used between the antenna and the GPS receiver itself.  If low loss cable is used, cable lengths over 300 meters (1000 feet) meters can be used without any degradation to the GPS signal.

Adding amplifiers however, can cause more problems than they solve.  Extra noise can be introduced by the amplifier and nearby transmitters, e.g. cellular or mobile telephone transmitters, can cause overloading of an amplifiers input, which could cause loss of satellite signals.

The GPS25 has been specially designed to overcome these problems.  Ultra low noise amplifiers have been used; together with two band pass filters.  The noise figure of the GPS25 is less than 3 dB and signals in the cellular or mobile frequency bands are rejected by more than 70 dB (see plots below).

Various Options and Configurations Available

The GPS25 can be configured to suit your exact requirements. The different configurations and options are explained below:

• DC voltage is normally received from the GPS receiver and passed through the GPS25 amplifier to the antenna. However, by removing an internal jumper, this DC voltage is not passed to the external antenna. This is useful when a passive antenna is used.
• Option 01 adds an external DC power connector. This allows the GPS25 to be powered from an external power supply source of 3.3 to 5 volts at 40 mA (useable from 3.0 volts). This is used if the GPS receiver does not supply its own voltage.
• Option 2,3 and 5 allow different connectors to be used on the GPS25. Note for large quantity orders (>50), the GPS25 can be manufactured with different connectors as standard, so adapter don't have to be used.
• Option 04 replaces the input SMA connector with an OCX connector. This allows antennas with OCX connectors to be connected to the GPS25 directly. The GPS25 output connector, that connects to the GPS receiver, remains an SMA type.

High Quality of Construction

Don't be fooled by the price.  The GPS25 is made to the highest standards.  The RF circuits are housed in an aluminum enclose which has been milled out of a solid piece of aluminum. 

Low  Price

The GPS25 breaks the price barrier for inline GPS amplifiers, costing typically half that of competitive units.  Refer to www.ptsyst.com/page5e.html for more details.

GPS25 SPECIFICATIONS

GPS25 Signal Plots

The above two plots show how the gain of the GPS25 is optimized for the center frequency of the GPS signal. Out of band signals from Cellular transmitters are attenuated by over 70 dB.