What Your FWD/REV Power Meter Is Actually Showing

A forward/reflected power meter is one of the most useful instruments in a ham radio station. It is also one of the most misunderstood.

The two common shortcuts are:

• “Forward power is the power being radiated.”
• “Reverse power is the power being lost.”

Both statements are too simple.

A FWD/REV wattmeter does not directly measure radiated power. It does not directly measure antenna efficiency. It does not directly measure feed-line loss. It does not even know whether the load is an antenna, dummy load, tuner, filter, wet connector, long coax run, or a badly installed matching network.

What it measures is much more specific:

The meter is not watching electrons disappear

When the meter shows 100 W forward and 10 W reflected, it is tempting to say:

• “I am transmitting 100 W.”
• “The antenna is rejecting 10 W.”
• “I am losing 10 W.”
• “Only 90 W is being radiated.”

Those statements may sound practical, but they mix several different RF concepts into one oversimplified story.

The meter is not measuring radiation. It is not measuring heat. It is not measuring what the antenna finally does with the energy it accepts. It is measuring wave components on the transmission line at one location.

That location matters. A meter at the radio, a meter after the tuner, and a meter at the antenna feedpoint can all show different numbers, and all three readings can be correct.

What forward power really means

Forward power is the power associated with the wave traveling from the source side toward the load side at the meter location.

That is not automatically the same as transmitter output power, and it is not automatically the same as radiated power.

Some of that forward-traveling power may later:

• be dissipated as heat in the coax;
• be lost in connectors, relays, traps, filters, or a tuner;
• reach the antenna feedpoint;
• be accepted by the antenna system;
• be converted into heat in coils, conductors, ground loss, or matching parts;
• be radiated;
• be reflected back because of an impedance mismatch.

Only one of those outcomes is useful radiation.

So when a meter near the transmitter says 100 W forward, the technically correct statement is:

What reflected power really means

Reflected power is the power associated with the wave traveling from the load side back toward the source side at the meter location.

That reflected wave usually exists because something downstream did not accept all of the incident wave at that encounter. The cause may be the antenna impedance, a tuner output, a connector transition, a filter, a damaged coax section, or any other discontinuity.

But reflection is not the same as loss.

A reflected wave may later be:

• re-reflected by a tuner or transmitter output network;
• absorbed by the transmitter output stage or protection network;
• absorbed by an isolator or circulator load;
• dissipated as heat during additional trips through the feed line;
• partly delivered to the antenna after another reflection.

That is why saying “10 W reflected means 10 W lost” is wrong. The reflected wave is real, but it is not automatically destroyed at the antenna.

How VSWR is derived from FWD and REV

Most shack VSWR meters do not physically scan along the coax to find voltage maxima and minima. They infer VSWR from the ratio between forward and reflected wave components.

The voltage reflection coefficient magnitude is:

VSWR is then:

Return loss is another way to describe the same reflection:

For example, if the meter shows:

• Forward power: 100 W
• Reflected power: 11.1 W

then:

A 2:1 VSWR means about 11.1% of the incident wave is reflected at that reference plane. It does not mean 50% of your power is lost. It does not mean half your power is radiated. It simply describes the wave ratio caused by the mismatch at that point in the system.

The useful but dangerous subtraction: forward minus reflected

Many operators use this formula:

This can be useful, but only if you understand what it means.

At a given point in a reasonably well-behaved transmission line, forward power minus reflected power is the net real power flowing past that point toward the load.

But that is still a local statement.

Meter location	What FWD − REV roughly tells you	What it does not tell you
At the transmitter	Net power leaving the transmitter area into the feed system	How much reaches the antenna
After the tuner	Net power entering the line on the antenna side of the tuner	Whether the transmitter sees the same mismatch
At the antenna feedpoint	Net power accepted by the antenna system	How much of that accepted power is radiated

Even at the antenna feedpoint, accepted power is not automatically radiated power. The antenna system may accept power and then waste part of it as heat in loading coils, traps, conductors, lossy ground, poor radials, or matching components.

A more complete expression is:

where η_radiation is the radiation efficiency of the antenna system.

Why meter location changes the story

Consider this station:

Now place the meter in different locations.

Meter between transmitter and tuner

The tuner may present a nice 50 Ω load to the transmitter. The meter may show very little reflected power and a pleasant VSWR.

That does not prove the antenna is matched. It proves that the transmitter side of the tuner is matched at that location.

Meter between tuner and coax

Now the meter may show high forward power and high reflected power because the feed line on the antenna side of the tuner is operating with standing waves.

That does not automatically mean the transmitter is unhappy. The tuner may still be doing its job at its input while the antenna-side line carries a high VSWR.

Meter at the antenna feedpoint

This is the closest location for measuring the actual antenna feedpoint mismatch. Here, FWD − REV is closest to the power accepted by the antenna system.

But even here, the meter still does not know how much of that accepted power becomes useful radiation.

A lossy coax can make SWR look better than it is

This is one of the most important practical traps in HF systems.

Suppose the antenna itself has a 2:1 VSWR. At the antenna, about 11.1% of the incident power is reflected.

Now place a long, lossy coax between the transmitter and the antenna. The forward wave is attenuated on the way to the antenna. The reflected wave is attenuated again on the way back to the shack.

By the time the reflected wave reaches the transmitter-end meter, it may be much smaller.

The shack meter may therefore show a comfortable VSWR, not because the antenna is well matched, but because the coax has hidden the reflection by converting RF into heat.

Example with 3 dB coax loss

Assume:

• 100 W forward at the transmitter end;
• 3 dB coax loss one way;
• 2:1 VSWR at the antenna.

The antenna receives only about 50 W on the first trip because the cable lost half the power. With a 2:1 mismatch, about 11.1% of that is reflected, or roughly 5.6 W.

That reflected wave then loses another 3 dB on the way back to the shack, so the transmitter-end meter sees only about 2.8 W reflected.

At the shack, the meter may show:

• Forward: 100 W
• Reflected: about 2.8 W
• Indicated VSWR: about 1.4:1

The antenna itself was still 2:1. The feed line made the shack SWR look better.

A tuner can make forward power look strange

A tuner does not magically destroy reflected power. It transforms impedance. On the transmitter side, it can present a comfortable load. On the antenna side, the line may still contain a large forward and reverse wave.

In a low-loss system, reflected energy from the antenna can reach the tuner and be re-reflected back toward the antenna. As a result, a meter on the antenna side of the tuner may show forward power greater than the transmitter’s net output.

That sounds impossible only if we wrongly assume that “forward power” always means “fresh power just created by the transmitter.” It does not. It means forward-traveling wave power at that point.

Example with a 3:1 load VSWR

For 3:1 VSWR:

That means 25% of the incident wave is reflected at the load.

If the net delivered power is 100 W:

A meter on that line could show:

• Forward: about 133 W
• Reflected: about 33 W
• Net: about 100 W

That does not mean the transmitter is producing 133 W. It means the line contains forward and reverse traveling-wave components whose difference is 100 W.

Low SWR is not the same as efficiency

A low SWR only means that the impedance seen at the measurement point is close to the meter’s reference impedance, usually 50 Ω.

It does not prove that the antenna system is efficient.

System	Possible SWR	What the meter cannot tell you
Dummy load	Excellent	Almost no useful radiation
Short loaded antenna with a lossy coil	May look acceptable	How much power becomes heat in the coil
Vertical with poor ground	May look very good	How much power is lost in soil or radial loss
Long lossy coax feeding a bad load	May look better at the radio	How much power was burned in the coax
Tuner at the radio	May show 1:1	What happens on the antenna side of the tuner

This is why the phrase “my SWR is good, so my antenna is good” is technically weak. A good antenna needs more than a comfortable impedance match. It also needs useful current distribution, reasonable loss resistance, a suitable radiation pattern, proper common-mode control, and installation conditions that support the intended job.

High SWR is not automatically disaster either

The opposite mistake is also common. High SWR does not automatically mean that most of your power is being lost.

In a short, low-loss feed line, a moderate mismatch may cost very little real power. The main practical concerns are different:

• transmitter foldback;
• PA stress;
• tuner loss;
• higher feed-line voltage and current;
• extra heating in real coax;
• arcing or heating in traps, ferrites, relays, baluns, or connectors;
• confusing meter readings.

So high SWR is not automatically high loss, but it can increase stress and can increase real losses in practical components.

What the meter cannot tell you

A basic FWD/REV power meter cannot tell you:

• whether the load is inductive or capacitive;
• whether the antenna is resonant;
• where the mismatch is located;
• whether the reflection came from the antenna, a connector, a filter, or a cable fault;
• how much power the feed line dissipated;
• how much accepted power became heat in the antenna system;
• how much power was radiated;
• what the radiation pattern is;
• whether common-mode current is present;
• whether the signal is going in a useful direction.

It also has its own limitations. Directional coupler accuracy depends on frequency response, calibration, detector behavior, power level, and especially directivity. When reflected power is small compared with forward power, poor directivity can make small readings unreliable.

Better wording for real stations

Instead of saying:

• “My forward power is 100 W, so I am radiating 100 W.”

say:

• “My meter shows 100 W forward at this point in the line.”

Instead of saying:

• “I have 10 W reflected, so I am losing 10 W.”

say:

• “My meter shows a 10 W reverse-traveling wave at this point.”

Instead of saying:

• “My SWR is 1:1, so my antenna is efficient.”

say:

• “The impedance match at this measurement point is good.”

Instead of saying:

• “My tuner removed the reflected power.”

say:

• “My tuner transformed the impedance so the transmitter sees a better match.”

The clean mental model

A FWD/REV power meter is not a radiated-power meter and not a loss meter.

It is a local traveling-wave meter.

Once you separate these ideas, many old arguments disappear. Reflected power is not automatically lost power. Forward power is not automatically radiated power. Low SWR is not automatically high efficiency. High SWR is not automatically disaster.

The meter is telling the truth, but only about what it can actually see.

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