A directional coupler is one of the most critical components inside any RF amplifier or station controller. Its job is to measure two independent signals:

• Forward power traveling toward the antenna

• Reflected power coming back toward the amplifier

With those measurements, the controller can compute SWR, monitor operating conditions, and detect dangerous mismatch events.

But SWR is only part of the story—
the fastest way to destroy an LDMOS transistor is not high SWR… it's over-drive.

⚠️ Over-Drive: The #1 Cause of LDMOS Device Failure

High SWR can cause stress, overheating, and eventual device failure if left unchecked.
But an LDMOS device will usually survive short SWR excursions as long as drive, current, and temperature remain controlled.

Over-drive is a different story.

When excessive RF drive hits the gate:

• The device enters avalanche or non-linear conduction

• Internal junction temperatures rise almost instantly

• Safe operating area is violated

• The LDMOS can fail in microseconds

Even a brief key-up at excessive drive levels can be fatal.

For this reason, over-drive protection must be extremely fast—faster than thermal systems, and even faster than typical SWR monitoring.

✔ How the Directional Coupler Protects the Amplifier

A coupler provides the raw data needed to detect:

• Forward power spikes

• Reflected power surges

• Sudden gain changes

• Transient overload events

• Conditions that suggest over-drive or failure of driver stages

• Mismatch conditions that raise device stress

With accurate, real-time forward/reflected power information, the controller can:

• Reduce drive power

• Remove bias

• Shut down the amplifier

• Log the event

• Protect the LDMOS device before damage occurs

This is where RayCoupler comes in.

🔶 RayCoupler — The RF StateSide Precision Directional Coupler

RF StateSide developed RayCoupler to be a high-performance sensing module specifically for modern LDMOS amplifiers.
RayCoupler is designed to:

• Deliver fast, accurate forward and reflected power measurements

• Operate properly from low power to multi-kilowatt levels

• Provide clean, predictable coupling suitable for ADS1115 or similar ADCs

• Integrate directly with RF StateSide controllers

• Enable both SWR protection and rapid over-drive detection

• Maintain stability across multiple HF bands

• Provide the precision needed for advanced protection firmware

Paired with RaySspaController, RayCoupler becomes the sensing backbone of the entire protection chain.

🛡 RF StateSide Protection Philosophy

RF StateSide designs focus on keeping modern high-power LDMOS devices operating within safe limits. The combination of:

• RayCoupler (high-speed RF sensing)

• RaySspaController (smart protection logic)

…creates a system capable of protecting against:

• Dangerous SWR conditions

• Faulty antennas or feed lines

• Driver-stage failures

• Sudden power spikes

• Over-drive events — the fastest and most lethal failure mode

The result is a high-performance system built for reliability, repeatability, and long device life.