Low Input Gain

If the cable loss reduces the LNA gain provided by the selected antenna to less than 15 dB (20 dB if HDR Mode is enabled), a low-noise amplifier must be added in-line between the antenna and the receiver. The in-line amplifier must provide sufficient gain to ensure the RF input gain to the receiver is provided within the range described in Receiver Input Gain Requirements. The in-line amplifier should be installed as close to the GNSS antenna as possible to ensure the GNSS signal is amplified when the signal to noise ratio is at its highest. Depending on the power requirements of the amplifier, the configuration of the RF equipment will vary, as shown in the following table.

Solutions for Low Input Gain based on RF Equipment Power Requirements

Input Voltage

Total Current Draw

Solution

Additional Equipment Required

The antenna LNA and in-line amplifier both accept +5.0 VDC.

< 200 mA

Connect the in-line amplifier directly to the receiver, as shown in In-Line Amplifier Powered by the Receiver.

  • In-line amplifier

> 200 mA

Add a power supply for the in-line amplifier and a bias-T to inject the supply in the RF line, as shown in In-Line Amplifier Powered from an External Power Supply.

  • In-line amplifier

  • External power
    supply

  • Bias-T

Both the antenna LNA and the in-line amplifier require a supply voltage other than +5.0 VDC but they both accept the same input voltage.

Any

Add a power supply and a bias-T to inject the supply in the RF line, as shown in In-Line Amplifier Powered from an External Power Supply.

  • In-line amplifier

  • External power
    supply

  • Bias-T

The antenna LNA and in-line amplifier require different input voltages.

Any

Add a power supply for the in-line amplifier, a supply for the antenna, and a bias-T, as shown in In-Line Amplifier and Antenna Powered by Separate Supplies.

  • In-line amplifier

  • External power
    supply

  • Bias-T

Current Requirement

As shown in Table: Solutions for Low Input Gain based on RF Equipment Power Requirements, the total amount of current required by the in-line amplifier and the GNSS antenna LNA is a factor when determining how to set up the RF equipment. NovAtel OEM7 receivers can provide up to 200 mA at +5.0 VDC on the center conductor of the RF port. Therefore, if the combined current draw of all the RF equipment connected to the port, including the in-line amplifier, is less than 200 mA, the receiver can supply the power.

For example, if the selected antenna’s LNA requires 50 mA and there is no other equipment between the antenna and the receiver that draws current, an in-line amplifier that draws 10 mA can be used without the addition of an external supply.

Amplification Requirement

Select an in-line amplifier that increases the signal gain by the amount necessary to result in an overall gain of +25 dB, as shown in the formula below. Be sure to take into account the loss created by any additional equipment being used with the in-line amplifier, such as bias-Ts.

AMPLIFICATION = 25 dB + LOSSCABLE + LOSSOTHER - GAINANTENNA

For example, if the selected antenna LNA provides +30 dB gain and the cable has a loss of -20 dB, then +15 dB amplification must be added.