A Better Antenna
A full-size wire vs. a short loaded whip can be 6 dB or more on the low bands. That's a whole S-unit, both ways: you hear better too. Which antenna?
KENTUCKY PORTABLE CLUB • FIELD KNOWLEDGE
POWER, dB & S-UNITS
Does 100 watts really beat 10? By less than you'd think. What decibels and S-units actually mean, why QRP works, and where your next S-unit is really hiding.
MEMORIZE THESE
The Big Four
Hams talk in decibels (dB) because radio signals cover a huge range of power. Here's the short version.
2×
POWER = +3 dB
Doubling your power is only half an S-unit. 50 W to 100 W is barely noticeable on the other end.
4×
POWER = +6 dB = 1 S-UNIT
It takes four times the power to move their meter one S-unit. 25 W to 100 W is one S-unit.
10×
POWER = +10 dB
Ten times the power is about 1⅔ S-units. 10 W to 100 W is under two S-units.
20×
POWER = +13 dB
QRP (5 W) to 100 W is only about 2 S-units. An S9 signal at 100 W is still about S7 at 5 W.
THE COMMON MIX-UP
"Doubling Power = 1 S-Unit"?
A lot of hams say this, but it's not quite right. One S-unit is 6 dB (the standard), and doubling is 3 dB, so doubling gets you half an S-unit. You need to quadruple your power for a full S-unit. That's why going from 100 W to a 1,500 W amplifier, which is 15 times the power, only moves the needle about 2 S-units.
CALCULATOR
What Would They Hear?
Start with the report you're getting now, then change your power, antenna or coax and see where their S-meter lands.
Antenna numbers are ballpark. Height, ground and direction change them a lot.
THE POWER LADDER
From QRP to the Legal Limit
Every step compared with 5 W (a typical QRP rig) and with 100 W (a typical base rig).
| POWER | VS. 5 W | S-UNITS VS. 5 W | VS. 100 W | S-UNITS VS. 100 W |
|---|
Notice how flat the top of the ladder is. From 100 W to 1,500 W, 15 times the power, the cost and the battery drain go way up for about 2 S-units.
CHEAPER THAN AN AMP
Where to Find Your Next S-Unit
Every one of these can be worth as much as quadrupling your power, and most of them cost little or nothing.
Up and Out
Raising a dipole, or adding radials under a vertical, can add 3–6 dB. On VHF, height is everything. Radial calculator
Stop Losing It
Long runs of thin coax, high SWR on coax, and wet or old cable quietly eat dB. On VHF/UHF it can be most of your power. Coax loss
CW & Digital
A narrow CW signal is roughly 10 dB or more easier to copy than SSB at the same power. FT8 decodes signals you can't even hear. Changing mode can be worth more than an amplifier. CW practice
Pick Your Band
The right band at the right time beats any power level. A band that's open is worth far more than 10 dB on one that isn't. Radio conditions
Point It
A beam, or just orienting your dipole broadside toward the station, adds several dB where it counts. A delta loop or vertical gets you lower angles for DX. Loops
KNOW YOUR METER
About That S-Meter
What S9 Means
- One S-unit = 6 dB. S1 through S9 covers 48 dB.
- On HF, S9 = 50 microvolts at the antenna jack (−73 dBm, 50 Ω). On VHF/UHF the standard puts S9 20 dB lower (−93 dBm).
- Above S9, meters switch to dB: "S9 +20" means 20 dB above S9, more than 3 S-units.
- An S-unit is a power ratio. One S-unit up is 4× the power arriving at the receiver.
Most Meters Fib a Little
- Few radios are calibrated. Many show only 3–4 dB per S-unit at the low end, so readings look closer together than they are.
- The preamp and attenuator change the reading without changing the signal.
- Band noise sets the floor. If the noise reads S5, an S5 signal is buried. What matters is how far the signal is above the noise, not the number.
- For a fair A/B test, swap antennas or power quickly and have the other station watch the same meter. Fading makes slow tests meaningless.
IN THE FIELD
What This Means for POTA & SOTA
- Cutting power to save battery barely costs you. 100 W → 50 W is half an S-unit, but it roughly halves your transmit current. See the battery calculator.
- QRP works because of the math. 5 W is only about 2 S-units below 100 W. If they hear you S9 at 100 W, they'll still hear you S7 at 5 W.
- Spend on the antenna, not the amplifier. A good antenna helps you transmit and receive. An amp only helps one direction, and hunters can't work you if you can't hear them.
- Hunters with big stations hear you better than you hear them. If you hear them S5, they may be hearing you S3. Keep calling.
- Reports are relative. A "5-5" one day and "5-9" the next can be propagation, not your gear.
- Need the numbers? The decibel calculator converts watts, dBm and dBW.
Get Outside. Get On The Air.
IT'S NOT THE WATTS. IT'S THE ANTENNA.
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