SWR POWER METER : Making of a swr bridge

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SWR power bridge (or SWR meter/standing wave bridge) is a device used in radio frequency (RF) systems, primarily in amateur radio and communications, to measure the Standing Wave Ratio (SWR) and often the forward and reflected power of a transmission line and its load (usually an antenna). This measurement helps ensure the system components are impedance-matched for maximum power transfer.
Function and
An SWR power bridge (often called an SWR bridge or VSWR bridge) is a device used in RF systems to measure:

Forward power (power going from transmitter to antenna)

Reflected power (power coming back toward the transmitter due to mismatch)

SWR (Standing Wave Ratio), which indicates how well the antenna is matched to the transmission line.

A tandem match coupler is a widely-used type of directional coupler for RF power and SWR measurement. It is the heart of many ham-radio SWR meters and wattmeters (including the classic Bird and ARRL design

🧩 Tandem Match Circuit

The two transformers are wound on ferrite cores (often FT-50-43 or FT-82-43 for HF), with a single-turn primary (the coax shield or a copper strap) and multiple-turn secondaries.


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🔧 Typical Build Details

Ferrite core

FT-43 material for HF

Tiny toroids for cleaner coupling


Turns

Primary: 1 turn (the transmission line)

Secondary: 20–30 turns


Diodes

1N34A (germanium) or

Schottky diodes (1N5711) for better sensitivity


Coupling factor

Usually around −30 to −40 dB

📡 Advantages of Tandem Match
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Very accurate over wide frequencies (1–60 MHz)

High directivity → good separation of FWD/REV

Stable with power (works from a few mW to hundreds of watts)

Easily home-brewable

How an SWR Power Bridge Works

An SWR bridge samples a small portion of the RF energy in both directions using:

1. Directional coupler / transformer

It separates:

Forward wave

Reverse wave


2. Detector diodes
Convert RF samples to DC voltages proportional to forward and reverse power.

3. Meter or display
Shows SWR or forward/reflected power based on detector output

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