Single-sideband (SSB) is a form of amplitude modulation. In SSB the carrier and one of the sidebands are suppressed, leaving just a single sideband. That reduces the required bandwidth (about half of conventional AM) and concentrates the transmitter power into the remaining sideband, making SSB much more efficient for voice on HF and for long-distance communications.

Spread-spectrum is a family of techniques that spreads a (usually already-modulated) signal over a wide range of frequencies; it is not itself a specific form of modulation. Packet radio is a data protocol/format that can use various modulation methods but is not a modulation mode itself. Phase-shift keying (PSK) is a digital modulation technique that conveys information by changing the phase of the carrier; although binary PSK can be viewed mathematically as switching the carrier between +1 and -1, PSK is categorized as phase modulation rather than conventional amplitude modulation, so single-sideband is the correct example of an amplitude modulation form.

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Angle modulation — frequency modulation (FM) or phase modulation (PM) — is commonly used for VHF packet radio. Packet transmissions are digital and benefit from a modulation that keeps the signal amplitude constant so that amplitude noise and fading have less effect; FM and PM are amplitude-stable (angle modulation) and provide good noise immunity and the capture effect. FM is also a permitted and widely implemented mode on VHF amateur channels, so FM (or PM) is the usual choice for packet.

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Single‑sideband (SSB) voice is often used for long‑distance or weak‑signal work on VHF and UHF because it uses less bandwidth and requires less transmitter power for a given intelligible signal than other common voice modes. That efficiency makes it easier to copy weak signals at the far end of a path.

Frequency modulation (FM) is commonly used for local simplex and repeater contacts on VHF/UHF, but FM’s capture or quieting effect that helps with strong signals makes it perform worse than SSB on weak, long‑distance signals. Phase modulation (PM) is closely related to FM, and Digital Radio Mondiale (DRM) is a digital broadcasting mode used on shortwave; neither is typically used for weak‑signal voice contacts on VHF/UHF in amateur practice.

Memory aids / mnemonics:

• Single Sidebands are a weaker or a smaller signal.

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VHF and UHF voice repeaters almost always use frequency or phase modulation. Frequency modulation (FM) is widely used because it provides good noise rejection and the capture effect, which helps a repeater reliably pass the strongest received signal. In amateur practice this is implemented as Narrow FM (about 15–20 kHz deviation/occupied bandwidth), unlike commercial broadcast FM which is Wide FM (about 200 kHz). Strictly speaking, what hams often call FM is actually phase modulation (PM), which is very closely related to FM and differs mainly in the audio frequency response (pre-emphasis and de-emphasis characteristics).

Memory aids / mnemonics:

• FM is the same modulation used by the FM radio in your car — easy to remember.
• Broadcast FM (music/talk radio) is Wide FM (~200 kHz); ham FM is Narrow FM (~15–20 kHz).
• Technically, ham "FM" is often PM; PM is FM with +6 dB/octave pre-emphasis and -6 dB/octave de-emphasis.

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Continuous Wave (CW), used for Morse code, is produced by switching an unmodulated carrier on and off. Because the transmitted information is only the presence or absence of the carrier (on/off), very little bandwidth is required. Other signal types that carry analog audio or image information require modulation that spreads the signal power over a wider range of frequencies, so they occupy more bandwidth than CW.

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By convention, upper sideband (USB) is used for single-sideband (SSB) voice on the 10‑meter HF band and on VHF and UHF bands. This is an agreed practice so that stations on those higher-frequency bands use the same sideband. Historically, the amateur bands below about 10 MHz commonly use lower sideband (LSB) while bands at 10 meters and above use USB, so the 10‑meter band (around 28 MHz) falls into the USB convention.

One practical exception is when communicating through an amateur satellite that uses a frequency-inverting linear transponder: in that case LSB transmitted on the uplink will appear as USB on the downlink (and vice versa), so operators may choose sideband with the transponder inversion in mind.

Memory aids:

• "Use USB for the upper bands" (10‑meter and above)
• Remember the historic split: LSB below ~10 MHz, USB above ~10 MHz
• For satellites with inverting transponders, LSB on uplink becomes USB on downlink

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AM has two mirror-image sidebands, upper and lower, and a carrier that contains a lot of power but no information. Single sideband (SSB) omits the carrier and one of the sidebands, putting all of its power into the remaining (single) sideband. That reduction in components reduces the occupied bandwidth — SSB voice signals typically occupy only a few kilohertz, much less than typical FM voice channels — and makes much more efficient use of transmitted power.

The narrower bandwidth does make SSB less susceptible to interference in the sense that it's a smaller target on the frequency dial, and it also means SSB causes less interference to other users of the band. However, SSB is still vulnerable to interference that falls inside its (smaller) bandwidth. Also, because SSB has no carrier for the receiver to lock onto, it is harder to tune correctly than AM or FM; the receiver must recreate the carrier accurately by local tuning.

Memory aids:

• "Single" sideband = one sideband → narrower bandwidth
• No carrier → harder to tune (no frequency reference)

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Single sideband (SSB) is a form of amplitude modulation that transmits only one of the mirror-image sidebands and usually omits the carrier. Because ordinary AM transmits two sidebands (one above and one below the carrier) it uses about twice the bandwidth of the original audio signal. SSB transmits only one sideband, so the RF bandwidth of the SSB signal equals the bandwidth of the modulating (audio) signal.

A typical communications-grade voice signal ranges from about 300 Hz up to about 3300 Hz, which is roughly a 3 kHz bandwidth. Some modern transceivers using DSP extend the low end down toward 100 Hz for better fidelity, but the conventional figure used for SSB voice bandwidth is approximately 3 kHz.

Memory aids:

• SSB has 3 letters → 3 kHz bandwidth.

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Carson's Rule gives a good estimate of the occupied bandwidth of an FM signal: bandwidth ≈ 2 × (maximum modulating frequency + peak frequency deviation). For typical ham FM voice on VHF repeaters the highest audio frequency is about 3 kHz and the commonly used peak deviation is about ±5 kHz. Plugging those numbers into Carson's Rule gives 2 × (3 kHz + 5 kHz) = 16 kHz. That is commonly rounded to about 15 kHz as the approximate occupied bandwidth for repeater FM voice signals. Narrower systems (lower deviation) will have correspondingly smaller bandwidths.

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Analog fast-scan TV transmissions use far more bandwidth than voice or slow-scan modes. In the United States the (now obsolete) NTSC analog TV standard used by amateur fast-scan TV occupies the same bandwidth as a standard TV broadcast channel, which is about 6 MHz. Therefore the approximate bandwidth of AM fast-scan TV transmissions is about 6 MHz.

Memory aids:

• Think “US TV channel ≈ 6 MHz”

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Continuous Wave (CW, i.e., on/off keyed Morse code) is essentially a single audio tone when it is "on." Because only a single frequency is transmitted (with abrupt on/off keying), the required bandwidth is very small — determined mainly by the keying speed and the rise/fall times that produce sidebands. For typical amateur CW keying speeds, the occupied bandwidth is on the order of a few hundred hertz; a commonly used approximation of the bandwidth needed to transmit a CW signal is about 150 Hz.

Memory aids:

• CW has the smallest bandwidth of common amateur modes.
• If a question asks which mode needs the least bandwidth, pick the smallest reasonable value listed.

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FM uses a constant carrier that is frequency-modulated by the audio. Because the carrier is always present, an FM receiver will generally reproduce the carrier noise or background when no one is speaking, and when two stations transmit on the same frequency the receiver usually locks onto the stronger signal (the "capture effect"), so you generally hear only the stronger station. Single sideband (SSB) signals have the carrier suppressed, so when someone isn’t talking essentially nothing is transmitted and overlapping conversations can still be partially heard together. For that reason, a disadvantage of FM compared with single sideband is that you normally can only receive one signal at a time on the same frequency.

The other statements are incorrect. FM typically gives better-sounding voice quality than SSB, and FM is actually easier to tune because the carrier provides a clear quiet point to tune to (this is why the term "full quieting" is used for a clear FM signal). High SWR is a function of antenna/feedline matching and affects all modulation types; it is not a disadvantage unique to FM.

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