Highland Technology’s Quadrature Modulator Geared for Aerospace Simulation

November 26, 2019 by Gary Elinoff

The P348 is designed for transducer simulation and provides carrier frequencies over a range of 0.5MHz to 20MHz.

The P348 is a new member of Highland Technology’s aerospace simulation suite. It is a mid-frequency dual-channel quadrature benchtop modulator with accurate DC-coupled baseband I and Q inputs. 



P348. Image from Highland Technology


The device is designed for a gamut of transducer simulations, including studies of eddy-current, inductive, and capacitive sensors.

The P348’s modulation can be used for hardware simulation of vibration, clearance, or gear tooth/blade tip sensors. The unit may also be used for classic RF modulation tasks.


P348 equivalent circuit

P348 equivalent circuit. Image from Highland Technology

It can also carry out proximity sensor and eddy current simulation. It can be employed to simulate jet engine blade tip sensors and semiconductor fabrication equipment sensors.

Users might also use the device to test mixing operations and single side band (SSB) generation.


What is Quadrature Modulation?

To fully understand the function of this new device, it may be helpful to brush up on I/Q signals and quadrature modulation

Two AC signals are in “quadrature” when they are out of phase by 90°. One is said to be the in-phase, or the “I” signal, and the other one—out of phase to “I” signal by 90°—is described as the “Q” signal. 

Because of the reference to I and Q signals, quadrature modulation is also referred to as IQ modulation.

In the picture below, the gray trace is the “I” signal, and the green trace is the “Q” signal—sine and cosine, respectively. They are exactly 90° out of phase. 


Phase convention

Phase convention. Image from Highland Technology

An RF signal is provided to a quadrature modulator, which will contain the means to produce another RF signal 90° out of phase with it. Then, there are two other inputs to the quadrature modulator, which might be two audio signals.

In two separate pathways, one audio signal is modulated by the sine wavelength, and the other audio signal is modified by the cosine wavelength. In this case, two AM signals are generated.

Finally, the two signals are added together in the output portion of the quadrature modulator.


Features of the P348

The device features two isolated, independent I/Q quadrature modulator channels. Its inputs and outputs are transformer isolated, and the input impedances are switchable between 50Ω, 100Ω, and HiZ. It is also customizable for frequency, matching, and amplitudes.


Block diagram of the P348

Block diagram of the P348. Image from Highland Technology

Highland Technology claims that the unit features "high linearity, wide dynamic range, and quantitative precision" and is compatible with benchtops or half-rack mounting. 



The device is packaged in an aluminum enclosure, measuring 7.0" (L) x 8.5" (W) x 2.25." External power supplies—24 volts DC, 500mA maximum—are included.


Input termination switches

Input termination switches. Image from Highland Technology 

Other specifications include: 

  • Carrier frequency input voltage range: 28Vpp nominal to 34Vpp maximum
  • I and Q inputs: ± 5V, -3dB at 1MHz, 500Ω
  • Output: 400mV p-p full scale for 50Ω impedance


Around the Industry

Signal Core offers the SC5413A and SC5412A IQ modulators. These devices operate at a range of 400MHz to 6MHz. They are aimed at applications in software-defined radio research, point-to-point radio, wireless communication testing, and multi-channel coherent systems.

The TRF3722 from Texas Instruments is a quadrature modulator in module form. It incorporates a PLL and a VCO, and it supports operation over a range of 400MHz to 4.2GHz.


Learn More About Quadrature Modulation

How to Process I/Q Signals in a Software-Defined RF Receiver

How to Use I/Q Signals to Design a Robust FSK Decoder

Understanding Quadrature Phase Shift Keying (QPSK) Modulation

Learning About Differential Quadrature Phase Shift Keying (DQPSK) Modulation