Extend HaLow range by adding external power amplifier

General
1

Hi all,

We are going to add an external bidirectional amplifier to off the shelf HaLow modem to increase TX power to maximum 30dBm that FCC defined as a conducted power limit.

Are there any similar experience?

Thanks

Behnam

2

While it’s not 30dBm, the Quectel FGH100MH boasts a 27dBm transmit power. As an off the shelf solution this might be worthwhile.

Interested to see how you go with an additional amplifier on the front end.

3

Hello ajudge,

Thank you for sharing the high-power module information.

I would like to clarify a few details regarding the TX power specification.

Typically, the TX power reported by manufacturers is the maximum output power measured using a simple modulation scheme, such as MCS0. In this case, the modulation is typically BPSK, which is much less sensitive to power amplifier nonlinearity.

As the modem switches to higher MCS levels, for example MCS9 (256-QAM), the transmitter must operate more linearly to maintain acceptable EVM performance. As a result, the output power must be backed off to keep the power amplifier within its linear operating region.

In addition, OFDM signals have a relatively high Peak-to-Average Power Ratio (PAPR), typically around 11 dB. This means the average transmit power must be approximately 11 dB below the amplifier’s peak output capability. For example, if the amplifier’s peak output power is 27 dBm, the average OFDM transmit power should be no more than approximately 16 dBm (27 - 11 = 16 dBm) to avoid significant signal distortion.

Regarding the external amplifier, this is a common approach for increasing the transmit power of wireless systems operating in TDD mode.

A bidirectional amplifier is connected between the modem and the antenna. This module contains a power amplifier ¶ in the transmit path and a low-noise amplifier (LNA) in the receive path.

A built-in RF power detector continuously monitors the modem’s output power. When it detects a transmit signal, the module automatically switches to TX mode, enabling the power amplifier. When no transmit signal is present, it switches back to RX mode, routing the received signal through the low-noise amplifier.

This automatic TX/RX switching is very fast and is designed to support TDD systems without requiring additional control signals from the modem.

Thanks

Behnam