Amateur radio is full of numbers: watts, volts, ohms, decibels, megahertz, microvolts, SWR, SNR, SINAD, dBi, dBd, and many more. At first they look like a pile of technical jargon, but they are really just the language of radio. Once you understand the units, you can read radio specifications, choose antennas, estimate station performance, troubleshoot problems, and communicate more precisely.

This article covers the most important units and measurements every amateur radio operator should know.

1. Frequency: Hz, kHz, MHz, GHz

Frequency is one of the most basic concepts in radio. It describes how many cycles per second a signal makes.

The SI unit is the hertz, written as Hz.

Common radio units:

Unit	Meaning	Example
Hz	hertz	audio tone, very low frequency
kHz	kilohertz, 1,000 Hz	7,100 kHz
MHz	megahertz, 1,000,000 Hz	145.500 MHz
GHz	gigahertz, 1,000,000,000 Hz	2.4 GHz

Amateur bands are usually described by either frequency or wavelength.

Examples:

Band	Approximate Frequency
160 m	1.8 MHz
80 m	3.5 MHz
40 m	7 MHz
20 m	14 MHz
2 m	144 MHz
70 cm	430 MHz

Frequency tells you where you are transmitting or receiving. It also affects propagation, antenna size, bandwidth, and licensing rules.

2. Wavelength: m, cm, mm

Wavelength is the physical length of one complete radio wave cycle. The SI unit is the meter, written as m.

Radio operators often use wavelength names for bands:

Band Name	Wavelength
40 m	about 40 meters
20 m	about 20 meters
2 m	about 2 meters
70 cm	about 0.7 meters
23 cm	about 0.23 meters

The relationship between frequency and wavelength is:

wavelength in meters = 300 / frequency in MHz

Examples:

145 MHz: 300 / 145 = about 2.07 m
433 MHz: 300 / 433 = about 0.69 m

This matters because antenna size is usually related to wavelength. A half-wave dipole for 40 m is physically much larger than a half-wave antenna for 2 m.

3. Power: W, mW, kW

Power tells you how much energy your transmitter sends out. The SI unit is the watt, written as W.

Common units:

Unit	Meaning
mW	milliwatt, 0.001 W
W	watt
kW	kilowatt, 1,000 W

Examples:

Equipment	Typical Power
Handheld radio	1 W to 5 W
Mobile VHF/UHF radio	25 W to 50 W
HF transceiver	100 W
QRP station	usually 5 W or less
Linear amplifier	hundreds of watts or more

More power can help, but it is not magic. Antenna efficiency, feedline loss, receiver noise, propagation, and operating skill often matter more than raw watts.

A useful rule:

Doubling power = +3 dB
Ten times power = +10 dB

So going from 5 W to 50 W is a 10 dB increase. Going from 50 W to 100 W is only 3 dB.

4. Voltage: V, mV, µV

Voltage is electrical pressure. The SI unit is the volt, written as V.

Common units:

Unit	Meaning
µV	microvolt, one millionth of a volt
mV	millivolt, one thousandth of a volt
V	volt
kV	kilovolt

In amateur radio, voltage appears in several places:

Use	Example
DC power supply	13.8 V
Battery voltage	12 V, LiFePO4 13.2 V
Receiver sensitivity	0.16 µV
RF voltage	depends on power and impedance

Many mobile and base radios are designed for about 13.8 V DC, because that is typical of a vehicle electrical system while charging.

Receiver sensitivity is often stated in microvolts. For example:

0.18 µV @ 12 dB SINAD

That means the receiver can detect a very weak signal and still produce usable audio.

5. Current: A, mA

Current is the flow of electric charge. The SI unit is the ampere, written as A.

Common units:

Unit	Meaning
mA	milliampere
A	ampere

Examples:

Device	Typical Current
Handheld receive mode	tens to hundreds of mA
Handheld transmit mode	around 1 A to 2 A
50 W mobile radio transmit	around 10 A to 15 A
100 W HF radio transmit	around 20 A to 25 A

Power, voltage, and current are related:

Power = Voltage × Current
W = V × A

Example:

13.8 V × 20 A = 276 W input power

The RF output may be 100 W, because the radio is not 100% efficient. Some energy becomes heat.

6. Resistance and Impedance: Ω

Resistance and impedance are measured in ohms, written as Ω.

Resistance applies mainly to DC circuits. Impedance applies to AC and RF circuits, where capacitance and inductance also matter.

Common amateur radio impedance values:

System	Typical Impedance
Most amateur coax systems	50 Ω
TV coax	75 Ω
Balanced feedline	300 Ω, 450 Ω, 600 Ω
Speaker audio	4 Ω, 8 Ω

Most modern amateur radios expect a 50 Ω antenna system. If the antenna system is not close to 50 Ω, the radio may reduce power or require an antenna tuner.

7. SWR: Standing Wave Ratio

SWR means Standing Wave Ratio. It describes how well the antenna system matches the transmitter and feedline.

SWR is written as a ratio:

1.0:1
1.5:1
2.0:1
3.0:1

General guide:

SWR	Meaning
1.0:1	perfect match
1.5:1	very good
2.0:1	usually acceptable
3.0:1	high; check antenna/feedline
above 3.0:1	may be unsafe for some radios

SWR does not directly tell you whether an antenna is “good.” It tells you about impedance match. A dummy load can have excellent SWR but radiates almost nothing. A real antenna can have a decent SWR but still be inefficient if badly placed, lossy, or poorly built.

8. Decibel: dB

The decibel, written as dB, is one of the most important units in radio.

Strictly speaking, dB is not an SI unit. It is a logarithmic ratio. It compares one value to another.

In radio, dB is used for:

• antenna gain
• feedline loss
• amplifier gain
• filter attenuation
• signal strength
• path loss
• receiver performance

Useful dB rules:

Change	Meaning
+3 dB	about double the power
-3 dB	about half the power
+6 dB	about 4 times the power
+10 dB	10 times the power
-10 dB	one tenth the power
+20 dB	100 times the power
-20 dB	one hundredth the power

Example:

If your coax has 3 dB loss, about half your power is lost in the feedline.

50 W transmitter power
3 dB feedline loss
about 25 W reaches the antenna

The decibel is powerful because gains and losses can be added.

Example:

Transmitter power: 50 W
Feedline loss: -2 dB
Antenna gain: +6 dBi
Net antenna-side gain effect: +4 dB

9. dBm and dBW

dBm and dBW are decibel units with fixed references.

Unit	Reference
dBm	relative to 1 milliwatt
dBW	relative to 1 watt

Common values:

Power	dBm	dBW
1 mW	0 dBm	-30 dBW
10 mW	10 dBm	-20 dBW
100 mW	20 dBm	-10 dBW
1 W	30 dBm	0 dBW
10 W	40 dBm	10 dBW
100 W	50 dBm	20 dBW

dBm is very common in receiver specs, spectrum analyzers, SDR software, link budgets, and weak-signal work.

Example:

-120 dBm = very weak signal
-90 dBm = stronger signal
-60 dBm = strong local signal

Less negative is stronger.

10. Antenna Gain: dBi and dBd

Antenna gain describes how an antenna concentrates radio energy in a particular direction compared with a reference antenna.

Two common units are dBi and dBd.

Unit	Reference
dBi	gain compared with an isotropic radiator
dBd	gain compared with a half-wave dipole

An isotropic radiator is a theoretical antenna that radiates equally in all directions. It is useful for math, but it does not physically exist.

A half-wave dipole is a real, common antenna.

Relationship:

dBi = dBd + 2.15
dBd = dBi - 2.15

Example:

Antenna gain = 5 dBd
Same gain = 7.15 dBi

Be careful when comparing antennas. A manufacturer using dBi may make the number look larger than one using dBd.

11. EIRP and ERP

EIRP means Effective Isotropic Radiated Power.

It is the apparent radiated power compared with an isotropic antenna.

ERP means Effective Radiated Power.

It is the apparent radiated power compared with a half-wave dipole.

These are important for regulations, repeater planning, satellite work, and link budgets.

Basic idea:

EIRP = transmitter power - feedline loss + antenna gain in dBi
ERP  = transmitter power - feedline loss + antenna gain in dBd

Example:

Transmitter: 50 W
Feedline loss: 3 dB
Antenna gain: 6 dBi

Power after feedline loss:

50 W - 3 dB = about 25 W

Antenna gain:

25 W + 6 dB = about 100 W EIRP

12. Bandwidth: Hz, kHz, MHz

Bandwidth is the amount of frequency space a signal occupies.

Common examples:

Mode	Typical Bandwidth
CW	very narrow, often a few hundred Hz
SSB voice	about 2.4 kHz to 3 kHz
AM voice	about 6 kHz or more
FM narrowband	around 12.5 kHz channel spacing
FM wideband	around 25 kHz channel spacing
Digital modes	varies widely

Bandwidth matters because radio spectrum is shared. A narrow signal uses less spectrum and may work better under weak conditions. A wide signal may carry better audio or more data but takes more space.

13. Signal Reports: RST and S-Units

Amateur radio commonly uses signal reports.

For CW and voice, the classic report is RST:

Letter	Meaning
R	readability
S	strength
T	tone, mainly for CW

Example:

59
599
57

For voice, 59 means perfectly readable and strong. In contests, 59 is often exchanged quickly and may not be a precise measurement.

Many receivers also show S-units on an S-meter.

A common convention:

1 S-unit ≈ 6 dB
S9 on HF ≈ -73 dBm
S9 on VHF/UHF ≈ -93 dBm

This is a guideline. Many radio S-meters are not perfectly calibrated.

Above S9, reports are often given in dB:

S9 + 10 dB
S9 + 20 dB
S9 + 40 dB

14. SNR: Signal-to-Noise Ratio

SNR means Signal-to-Noise Ratio.

It compares the wanted signal with the noise level.

SNR = signal level compared with noise level

It is usually measured in dB.

Examples:

SNR	Meaning
0 dB	signal and noise are about equal
10 dB	signal is clearly above noise
20 dB	good copy
30 dB	very clean signal

SNR is especially important for:

• HF weak-signal work
• digital modes such as FT8, JS8Call, packet, APRS, Winlink
• satellite communication
• EME
• SDR receiver displays
• link budget calculations

Digital modes often work at lower SNR than voice because computers can decode weak structured signals.

15. SINAD

SINAD means:

Signal + Noise + Distortion
divided by
Noise + Distortion

It is used mainly in receiver sensitivity testing, especially for FM voice receivers.

A common specification:

0.18 µV for 12 dB SINAD

This means that with a signal of 0.18 microvolts, the receiver produces audio with 12 dB SINAD, which is considered a usable audio benchmark.

When comparing receivers:

0.16 µV @ 12 dB SINAD

is generally more sensitive than:

0.25 µV @ 12 dB SINAD

because less signal is needed to reach the same audio quality.

16. Noise Figure: NF

Noise figure, written as NF, describes how much noise a receiver, preamp, or amplifier adds to a signal.

It is measured in dB.

Lower is better.

Examples:

Noise Figure	Meaning
0.5 dB	excellent
1 dB	very good
3 dB	moderate
6 dB	noisy

Noise figure is especially important at VHF, UHF, microwave, satellite, and weak-signal operation. On lower HF bands, atmospheric noise may dominate, so receiver noise figure is often less critical.

17. Noise Floor: dBm

The noise floor is the background noise level in a receiver or measurement system.

It is often shown in dBm.

Example:

Noise floor: -120 dBm
Signal: -100 dBm
SNR: 20 dB

A lower noise floor allows weaker signals to be detected. However, real-world noise from power supplies, electronics, thunderstorms, solar activity, and urban environments can raise the effective noise floor.

18. Return Loss

Return loss is another way to describe antenna mismatch. It is measured in dB.

Higher return loss is better.

Approximate comparison:

SWR	Return Loss
1.0:1	infinite, perfect
1.5:1	about 14 dB
2.0:1	about 9.5 dB
3.0:1	about 6 dB

Many antenna analyzers and VNAs show return loss as well as SWR.

19. Capacitance: F, µF, nF, pF

Capacitance is measured in farads, written as F.

In radio, practical values are usually much smaller:

Unit	Meaning
µF	microfarad
nF	nanofarad
pF	picofarad

Capacitors are used in:

• filters
• antenna tuners
• matching networks
• oscillators
• power supply filtering
• coupling and bypass circuits

Examples:

100 pF tuning capacitor
0.1 µF bypass capacitor
10 µF electrolytic capacitor

20. Inductance: H, mH, µH

Inductance is measured in henrys, written as H.

Common radio values:

Unit	Meaning
mH	millihenry
µH	microhenry
nH	nanohenry

Inductors are used in:

• antenna loading coils
• filters
• traps
• matching networks
• RF chokes
• oscillators

Examples:

2.2 µH coil
100 µH RF choke

Capacitors and inductors together form resonant circuits, which are central to radio tuning and filtering.

21. Battery Capacity: Ah and Wh

Battery capacity is commonly given in amp-hours, written as Ah.

Example:

12 V 20 Ah battery

This means the battery can theoretically supply:

20 A for 1 hour
or
1 A for 20 hours

In practice, usable capacity depends on battery chemistry, discharge rate, temperature, and cutoff voltage.

A better energy unit is watt-hour, written as Wh.

Wh = V × Ah

Example:

12.8 V × 20 Ah = 256 Wh

For emergency communication and portable radio, Wh is often more useful than Ah, because it includes voltage.

22. Temperature: °C and K

Temperature is commonly measured in degrees Celsius, written as °C.

Examples:

Radio operating temperature: -10 °C to +60 °C
Battery temperature limit: 0 °C to 45 °C while charging

The SI base unit is kelvin, written as K.

Kelvin is used in technical radio calculations involving thermal noise.

Important idea:

Higher temperature = more thermal noise

Most amateur operators use Celsius day to day, but kelvin appears in receiver noise and microwave engineering.

23. Time: s, ms, µs, UTC

Time is measured in seconds, written as s.

Common units:

Unit	Meaning
s	second
ms	millisecond
µs	microsecond

Time matters for:

• digital modes
• packet timing
• propagation delay
• satellite passes
• logging
• contests
• emergency nets

Amateur radio commonly uses UTC, Coordinated Universal Time, for logging and international contacts.

Example log entry:

2026-06-29 1415 UTC
14.074 MHz
FT8
9M2PJU
-12 dB

Using UTC avoids confusion between time zones.

24. Data Rate: bps and Baud

Digital radio uses data rates.

Unit	Meaning
bps	bits per second
baud	symbols per second

They are related, but not always the same.

If each symbol carries one bit:

baud = bps

If each symbol carries multiple bits:

bps can be higher than baud

Examples:

Mode/System	Related Unit
Packet radio	1200 bps, 9600 bps
RTTY	baud rate, shift
Digital voice	bit rate
Modems	baud and bps

25. Field Strength: V/m and dBµV/m

Field strength describes the strength of an electromagnetic field at a location.

Common units:

Unit	Meaning
V/m	volts per meter
mV/m	millivolts per meter
µV/m	microvolts per meter
dBµV/m	decibels relative to 1 microvolt per meter

Field strength is used in:

• coverage prediction
• repeater studies
• EMC/RFI work
• broadcast engineering
• regulatory measurements

Most casual amateur operators do not use field strength daily, but it is important for interference investigations and serious station engineering.

26. Modulation Measurements

Several units and ratios describe modulation quality.

Deviation

FM deviation is measured in Hz or kHz.

Example:

±5 kHz deviation
±2.5 kHz deviation

Too much deviation causes splatter or distortion. Too little deviation makes audio weak.

Modulation Percentage

AM modulation is often expressed as a percentage.

100% modulation

Overmodulation causes distortion and unwanted emissions.

THD

THD means Total Harmonic Distortion.

It is usually given as a percentage or in dB.

Lower THD means cleaner audio or cleaner signal reproduction.

27. Digital Quality Units: BER, MER, Eb/N0

Digital communication introduces more quality measurements.

Unit	Meaning
BER	Bit Error Rate
PER	Packet Error Rate
MER	Modulation Error Ratio
Eb/N0	Energy per bit to noise density ratio
C/N	Carrier-to-noise ratio
C/N0	Carrier-to-noise density ratio

For most amateur operators, BER is the easiest to understand.

Example:

BER = 1 × 10^-5

This means about 1 bit error in 100,000 bits.

Lower BER is better.

These measurements are common in digital voice, satellites, microwave links, and data systems.

28. Common Prefixes

SI prefixes are essential in radio.

Prefix	Symbol	Multiplier
pico	p	10^-12
nano	n	10^-9
micro	µ	10^-6
milli	m	10^-3
kilo	k	10^3
mega	M	10^6
giga	G	10^9

Examples:

100 pF
2.2 µH
13.8 V
500 mA
7 MHz
2.4 GHz

Be careful with capital letters:

m = milli
M = mega

So:

mW = milliwatt
MW = megawatt

Those are very different.

29. Quick Reference Table

Measurement	Unit	Used For
Frequency	Hz, kHz, MHz, GHz	operating frequency
Wavelength	m, cm	band names, antennas
Power	W, mW, kW	transmitter output
Voltage	V, mV, µV	power supply, signals
Current	A, mA	power draw
Resistance/Impedance	Ω	antennas, feedlines
Gain/Loss	dB	ratios
Power level	dBm, dBW	signal and RF levels
Antenna gain	dBi, dBd	antenna comparison
Match	SWR, return loss	antenna system
Sensitivity	µV, dBm, SINAD	receiver performance
Signal quality	SNR, SINAD	readability and audio quality
Noise	dBm, NF	receiver/noise performance
Capacitance	F, µF, pF	circuits and tuners
Inductance	H, µH	coils and filters
Battery capacity	Ah, Wh	portable/emergency power
Data rate	bps, baud	digital modes
Time	s, UTC	logs, digital timing

30. Practical Examples

Example 1: Feedline Loss

You transmit 50 W into a coax cable with 3 dB loss.

3 dB loss = half power

So only about:

25 W

reaches the antenna.

Example 2: Antenna Gain

Your antenna has 6 dBi gain.

6 dB gain = about 4 times power in the favored direction

If 25 W reaches the antenna:

25 W × 4 = about 100 W EIRP

Example 3: Receiver Signal

Your SDR shows:

Noise floor: -120 dBm
Signal: -100 dBm

Then:

SNR = 20 dB

That is usually a very usable signal.

Example 4: Battery Runtime

Your radio draws:

1 A on receive
20 A on transmit

With a 20 Ah battery, runtime depends heavily on duty cycle.

If you transmit often, the battery drains much faster. For emergency work, always calculate using realistic transmit and receive time.

Conclusion

The most important amateur radio units are not just numbers on a specification sheet. They describe how your station actually works.

If you understand Hz, W, V, A, Ω, dB, dBm, dBi, dBd, SWR, SNR, SINAD, µV, Ah, and Wh, you can make better decisions about radios, antennas, feedlines, batteries, and operating technique.

A good amateur radio operator does not need to memorize every formula. But knowing what the units mean gives you a practical engineering sense: how much power is really reaching the antenna, how weak a signal your receiver can hear, how much loss your coax has, how long your battery will last, and why a better antenna often beats a bigger amplifier.