RF

RF (radio frequency), in the context of CRT televisions, refers to an analog signal format in which composite video and audio are modulated onto a radio frequency carrier wave for transmission over coaxial cable or antenna connections. It is the oldest and most universal method of delivering a television signal to a receiver, and was the only input available on many CRT sets manufactured before the widespread adoption of baseband audio/video jacks in the 1980s.

On the EveryCRT wiki, "RF" designates the signal format — the modulated carrier that combines picture and sound into a single connection. The physical connectors used to carry RF signals are documented separately: RF (F-type), RF (Belling-Lee), and RF (300Ω twin-lead).

How It Works

An RF television signal is created by taking a baseband composite video signal and an audio signal and modulating them onto a carrier wave at a specific channel frequency. The video information is transmitted using amplitude modulation (specifically vestigial sideband, or VSB, modulation), while the audio is transmitted using frequency modulation on a subcarrier offset from the video carrier — typically 4.5 MHz in NTSC System M countries and 5.5 to 6.5 MHz in PAL/SECAM systems.

At the television receiver, an internal tuner selects the desired channel frequency and demodulates the RF signal back into its baseband video and audio components for display and playback. This modulation-demodulation process inherently introduces signal degradation beyond what is already present in the composite video signal, making RF the lowest-quality common analog video connection.

History

RF is the original television signal format. From the earliest commercial broadcasts in the late 1930s and 1940s, television signals were transmitted over the air as modulated RF carriers received by antennas. For the first several decades of consumer television, the antenna input was the only way to feed a signal into a TV set — there were no dedicated audio/video input jacks.

When VCRs, early home computers, and video game consoles appeared in the 1970s, they needed a way to connect to existing television sets. Since most TVs of the era lacked composite video inputs, these devices included built-in RF modulators that converted their output to a signal on an unused channel — typically channel 3 or 4 in North America — which could be received through the TV's antenna input. This approach allowed new devices to work with the enormous installed base of TVs that only had antenna connections.

By the mid-1980s, consumer CRT televisions increasingly included direct composite video and audio inputs (RCA jacks), reducing the need for RF modulators. Through the 1990s and 2000s, higher-quality connections such as S-Video (Y/C), Component (YPbPr), and eventually HDMI further displaced RF for device interconnection. However, RF antenna/cable inputs remained standard on virtually all CRT televisions throughout the entire production era, as they were required for receiving broadcast television and cable TV signals.

Channel Frequencies

RF television signals are assigned to numbered channels within the VHF (Very High Frequency) and UHF (Ultra High Frequency) bands. The specific frequencies vary by region:

Region	VHF Channels	UHF Channels	Channel Bandwidth
Americas (System M/NTSC)	2–13 (54–216 MHz)	14–83 (470–890 MHz)	6 MHz
Europe (Systems B/G, PAL/SECAM)	2–12 (47–230 MHz)	21–69 (470–862 MHz)	7 MHz (VHF) / 8 MHz (UHF)
UK (System I, PAL)	—	21–68 (470–854 MHz)	8 MHz
France (System L, SECAM)	2–10 (47–216 MHz)	21–69 (470–862 MHz)	8 MHz

Consumer RF modulators (those built into game consoles, VCRs, and standalone units) typically output on a single selectable channel. In North America, channels 3 and 4 (61.25 MHz and 67.25 MHz respectively) were the standard choices because these two channels were rarely assigned to broadcast stations in the same market.

Signal Characteristics

Parameter	Value
Signal type	Modulated RF carrier (analog)
Content	Composite video + audio on a single carrier
Video modulation	Amplitude modulation (vestigial sideband)
Audio modulation	Frequency modulation
Audio subcarrier offset	4.5 MHz (NTSC), 5.5–6.5 MHz (PAL/SECAM)
Resolution	480i (NTSC) / 576i (PAL/SECAM)
Impedance	75Ω (coaxial) or 300Ω (twin-lead)
Common connectors	F-type (Americas), Belling-Lee (Europe/Asia), 300Ω twin-lead screw terminals

Quality

RF sits at the bottom of the analog video quality hierarchy. Because the signal undergoes both modulation (at the source) and demodulation (at the TV's tuner), it suffers from all the artifacts inherent to composite video — dot crawl, cross-color, and limited color bandwidth — plus additional degradation from the RF encoding process itself. This can manifest as reduced sharpness, added noise, and interference patterns, particularly with inexpensive consumer-grade modulators that lack proper vestigial sideband filtering.

In order of increasing quality, the common analog video signal formats are:

1. RF — composite video + audio modulated onto an RF carrier (worst)
2. Composite (CVBS) — baseband composite video signal
3. S-Video (Y/C) — separate luminance and chrominance channels
4. Component (YPbPr) — separate luminance and color-difference channels
5. RGB — discrete red, green, and blue channels (best)

For retro gaming and CRT enthusiasts, even upgrading from RF to composite video provides a noticeable improvement in picture clarity, as it eliminates the losses from RF modulation and demodulation.

Use on CRT Televisions

The RF antenna/cable input is the single most universal connection found on CRT televisions worldwide. Every CRT TV with a tuner includes at least one RF input, and for many sets — particularly budget models and those manufactured before the mid-1980s — it is the only video input available.

Common RF input configurations on CRT sets include:

• Single F-type jack — standard in North America from the mid-1980s onward, typically labeled "ANT," "VHF/UHF," or "CATV"
• Separate VHF and UHF inputs — common on older North American and Japanese sets, often with an F-type jack for VHF and 300Ω twin-lead screw terminals for UHF
• Belling-Lee connector — the standard 75Ω push-on RF connector used throughout Europe, the UK, Australia, and much of Asia
• 300Ω twin-lead screw terminals only — found on the oldest sets, before coaxial inputs became standard

Many CRT televisions also include an RF output or loop-through jack, allowing the antenna signal to be passed to a second television set.

RF Modulators

An RF modulator is a device that converts baseband audio/video signals into a modulated RF signal. RF modulators were integral to the early home electronics ecosystem, appearing in several forms:

• Built-in modulators — included in VCRs, early home computers (such as the Apple II, Commodore 64, and ZX Spectrum), and video game consoles (Atari 2600, NES, Sega Master System, and many others)
• External/standalone modulators — small adapter boxes that accept composite video and audio inputs and output an RF signal, used to connect newer AV equipment to older TVs lacking direct inputs
• Switchbox modulators — common with game consoles of the 1970s and 1980s, these included a mechanical switch to toggle between the console's signal and the antenna feed

In North America, consumer RF modulators typically output on channel 3 or 4, with a physical switch to select between them. In PAL regions, modulators commonly output on channel 36 (UHF) or other locally appropriate channels.

See Also

• Composite (CVBS) — The baseband video signal that RF carries in modulated form
• RF (F-type) — 75Ω threaded coaxial connector (Americas)
• RF (Belling-Lee) — 75Ω push-on coaxial connector (Europe/Asia)
• RF (300Ω twin-lead) — Balanced twin-lead screw terminals