QRP versus 100 watts: what the extra power actually buys

Twenty times the power is two S units. The antenna is where the decibels actually are.

The short answer

Going from 5 W to 100 W is a gain of 13 dB, about two S units, which turns a marginal contact into a comfortable one but does not open a closed band. QRP costs you the difficult contacts and saves you battery weight, station cost and power supply complexity. For a home station, run 100 W. For portable operation, run 10 to 20 W.

5 W to 100 W: 13 dB, 2 S units
100 W to 1,500 W: 11.8 dB, 2 S units
Doubling power: 3 dB, half an S unit
Antenna height gain: Often 6 to 10 dB
QRP definition: 5 W CW, 10 W SSB
Battery life at 5 W: Three times longer

Power is the lever everybody reaches for first and the one that moves least. The decibel arithmetic is not intuitive: going from 5 W to 100 W, a twentyfold increase, is 13 dB. Going from 100 W to a full legal limit amplifier, a fifteenfold increase, is another 11.8 dB. Each of those is about two S units on the other operator meter, and neither opens a band that is closed.

Meanwhile, getting a wire antenna from 15 ft to 40 ft can be worth 6 to 10 dB on the paths that matter, for a fraction of the cost. That is the real reason experienced operators talk about antennas and not about power.

None of which means QRP and 100 W are equivalent. The difference is real; it is just smaller and more situational than beginners expect.

The arithmetic

Power in decibels

What each power step is worth at the far end

From	To	Gain in dB	S units
1 W	5 W	7.0 dB	About 1.2
5 W	10 W	3.0 dB	About 0.5
5 W	100 W	13.0 dB	About 2.2
10 W	100 W	10.0 dB	About 1.7
100 W	400 W	6.0 dB	About 1
100 W	1,500 W	11.8 dB	About 2
5 W	1,500 W	24.8 dB	About 4

One S unit is conventionally 6 dB, though few radios follow that convention accurately. The dB and power ratio calculator converts any pair of figures.

What QRP costs you

The marginal contacts. Roughly the bottom fifth of what a 100 W station works. Those are also the ones people remember, which is why the loss feels larger than it measures.
Pileups. Calling a rare station against fifty 100 W stations at 5 W is a long afternoon.
Poor conditions. When the band is barely open, power is exactly the thing that gets a signal through.
Casual voice contacts. SSB is the least efficient mode for the power. QRP on CW or FT8 works far better than QRP on voice.
Patience. QRP rewards operating skill and timing. That is genuinely enjoyable for some people and frustrating for others.

What QRP buys you

Battery life. A 5 W radio drawing under 2 A on transmit runs all day on a pack that a 100 W radio empties in three hours. For portable operating this is the entire argument.
Weight. A QRP radio, a small pack and a wire fit in a shoulder bag. A 100 W station needs a bigger pack and a bigger radio.
Station simplicity. No 30 A supply, no heavy DC wiring, no heat.
RF exposure headroom. A 5 W station passes an exposure evaluation almost anywhere, which matters enormously on a balcony or in an attic.
Cost. A capable QRP radio, a wire and a battery is a complete station for well under a thousand dollars.

Where the decibels actually are

Comparing upgrades

What each improvement is worth, and what it costs

Change	Typical gain	Cost	Verdict
Wire from 15 ft to 40 ft	6 to 10 dB	Rope and an afternoon	The best value in the hobby
Thin coax to low-loss coax on VHF	3 to 5 dB	$100 to $200	Large on VHF, small on HF
5 W to 100 W	13 dB	$400 to $900 radio difference	Real, and the obvious step
Dipole to a 3 element beam	5 to 7 dB, plus rejection	$3,000 installed	Excellent, and a project
100 W to 600 W	7.8 dB	$1,000 to $2,500	Diminishing, and a real one
Fixing a bad connector	1 to 10 dB	A few dollars	Free performance nobody counts

The ordering is the point. Almost every station has cheaper decibels available than the ones an amplifier sells.

The three radios this question resolves to

Three tiers

QRP, hybrid or full power

Choose by where the radio will spend most of its life, not by the maximum number on the spec sheet.

True QRP Not on Amazon

Backpack, summit and CW or digital operating

Not stocked by Amazon

QRP Labs

QRP Labs QMX+

A few watts, a handful of bands, negligible current draw and a price that makes a dedicated field radio easy to justify. On CW and digital modes it works far better than the power figure suggests.

Output 5 W
Draw Very low

Tradeoff
No SSB on the base configuration and no margin at all when conditions are poor.

Find comparable gear

Sold as a kit by QRP Labs, roughly $145

Sold by QRP Labs, not Amazon. The button searches the category.

The sensible middle $466.00

Portable operating that occasionally needs to be heard

Xiegu

Xiegu G90

Twenty watts is 6 dB above QRP and a quarter of the current draw of a 100 W radio, with a built-in tuner that handles a compromise field antenna. This is the power level most portable operators settle at.

Output 20 W
Tuner Built in

Tradeoff
Not enough for a difficult pileup, and its receiver is a step below the class above.

Check price

Full power home station $1,255.74

A house, a supply and an antenna in the air

Icom

Icom IC-7300

A hundred watts and a spectrum scope that shows you the whole band. For a home station there is no reason to run less, and the scope changes how you find contacts more than the power does.

Output 100 W
Scope Real time

Tradeoff
Needs a 30 A supply and is not a backpack radio.

Check price

A practical recommendation

For a home station, buy 100 W. There is no meaningful saving in buying less, and the radio can always be turned down.
For portable operating, run 10 to 20 W from the same radio or a dedicated small one. The battery difference is decisive and the signal difference is not.
Spend the money you did not spend on an amplifier on the antenna and its height. That is where the decibels are.
If you enjoy QRP as a discipline, enjoy it. It is a genuinely rewarding way to operate and it teaches more about propagation and timing than power ever does.
Buy the amplifier when your antenna is already as good as your lot allows and power is genuinely the remaining limitation. Most stations are not there.

Safety

RF exposure: you must evaluate your own station

The FCC requires every amateur station to perform a routine RF exposure evaluation and to keep the result. The categorical exemption that used to excuse amateurs by power level alone was removed, so there is no wattage below which you can simply assume you comply.

Radio frequency energy at close range is a real hazard, not a paperwork exercise. Transmitting at power into an antenna a few feet from a person, especially on the bands between 30 and 300 MHz where the exposure limit is at its strictest, can exceed the maximum permissible exposure for an uncontrolled environment.

Nothing on this page evaluates your station. The answer depends on your frequency, your power at the antenna, your antenna gain, your duty cycle and how close people actually get. Run the numbers for your own installation.

The exposure evaluation scales directly with power. A station that passes comfortably at 20 W may not at 100 W with the same antenna and the same neighbour. Re-run the numbers whenever the power changes.

How to run an RF exposure evaluation

Common questions

Questions people ask about this

How much difference is there between 5 watts and 100 watts?

Thirteen decibels, which is a little over two S units on the receiving station meter. On a strong path that is inaudible in practical terms. On a marginal path it is the difference between a contact and silence. It does not open a band that is closed, and it is smaller than the improvement most stations could get by raising their antenna.

Can I work the world with 5 watts?

Yes, routinely, particularly on CW and on digital modes such as FT8 which decode far below the noise floor. QRP operators hold every major award. What you give up is the marginal contacts, the pileups and the days when conditions are poor. On SSB voice, QRP is considerably harder than on CW or digital, because voice is the least efficient use of the power.

Is an amplifier worth buying?

Only once your antenna is as good as your property allows. Going from 100 W to 600 W is 7.8 dB, a little over one S unit, and it costs one to two thousand dollars plus a bigger supply, better feedline and a harder RF exposure evaluation. Almost every station has cheaper decibels available in the antenna system first, and most operators who buy an amplifier early regret the order.

What power should I run portable?

Ten to twenty watts. It is 3 to 6 dB above QRP, which is enough to make casual voice contacts practical, and it draws a fraction of the current a 100 W radio does, so the same battery lasts three times as long. Since battery capacity rather than signal strength is the real constraint on a portable activation, that trade is strongly favourable.

Does running less power damage anything?

No, and it helps in two ways. Reduced output runs the finals cooler, which matters a great deal on high duty cycle digital modes where continuous full output shortens the life of the radio. It also lowers your RF exposure figures, which is the difference between passing and failing an evaluation on a small lot or a balcony.

Keep going

Related on this site

Keeping your own cut lengths, SWR sweeps and exposure record? The Station Build & Antenna Planner is the paid version of these pages: 8 printable worksheets you fill in with your own numbers, plus the full PDF, $29.

Disclaimer Researched guidance for planning purposes, not professional engineering, electrical or legal advice. Antenna work, RF exposure, mast and tower work, grounding and battery handling all carry real risk that depends on your specific site and installation. Verify anything safety-critical against current FCC rules, the National Electrical Code and the manufacturer's own documentation, and hire a professional where the job calls for one. We research equipment from published specifications, regulatory documents and verified owner reviews rather than claiming hands-on testing we have not done.