Quick answer: RG59 is a 75 ohm coaxial cable with a 0.81 mm centre conductor and a braided shield, and it loses roughly 10 dB per 30 m at 1 GHz, about 50 percent more than RG6 over the same distance. That makes it a poor choice for satellite, MoCA or long HD-SDI runs, and a perfectly good one for short analogue CCTV drops, subwoofer feeds and short digital audio links where the signal band stays under a few megahertz. The connector matters as much as the cable: a 75 ohm BNC or F termination keeps the impedance constant, while a 50 ohm adapter adds a reflection.
RG59 survives because it is thin, flexible and cheap, and because a great deal of installed infrastructure uses it. Deciding whether to keep it comes down to two numbers: the highest frequency in the signal and the length of the run. Below about 6 MHz almost any coax works; above 500 MHz the difference between RG59 and RG6 becomes the difference between a link that closes and one that does not.
What is inside RG59
Conductor, dielectric and shield
The centre conductor is typically 0.81 mm, often copper-clad steel for strength in aerial runs. The dielectric is solid or foam polyethylene around 3.7 mm, and the shield is a braid, sometimes with a foil layer for better coverage. Foam dielectric lowers loss and raises velocity of propagation to about 0.8 of the speed of light; solid polyethylene sits nearer 0.66.
Why 75 ohm and not 50
75 ohm is the compromise that minimises loss for video and broadband signals, while 50 ohm maximises power handling and is used for radio equipment. Mixing the two at a connector produces a reflection that shows up as ghosting on analogue video and as return loss on digital links. A 50 ohm BNC on 75 ohm cable is a common field error because the connectors look identical.
Attenuation compared
| Frequency | RG59 | RG6 | RG11 |
|---|
| 100 MHz | About 3.2 dB | About 2.1 dB | About 1.5 dB |
| 500 MHz | About 7.4 dB | About 4.7 dB | About 3.3 dB |
| 1 GHz | About 10.5 dB | About 6.5 dB | About 4.5 dB |
| 3 GHz | About 19 dB | About 12 dB | About 8.5 dB |
Figures are typical attenuation per 30 m and vary with dielectric and shield construction. Treat them as a design aid, not a guarantee: a foil plus braid RG59 can be a decibel better than a single braid, and a badly terminated connector can cost more than the difference between cable types.
What RG59 still does well
Analogue video and short digital audio
Composite and CVBS signals occupy 5 to 6 MHz, where RG59 loses less than 1 dB per 30 m, so a 30 m CCTV drop is comfortable and a 100 m drop is still workable. Digital audio at 192 kHz sits well under 12 MHz and behaves the same way. Subwoofer feeds are also fine, because the signal is below 200 Hz and the only requirement is shielding to keep hum out.
Short SDI and composite routing
SD-SDI at 270 Mbit/s runs reliably over 100 m of RG59 in most installations, and 3G-SDI at 2.97 Gbit/s does not: the bit rate moves the energy spectrum above 1 GHz, where RG59 loses more than 10 dB per 30 m and the receiver equaliser runs out of range. That single change is why broadcasters standardised on RG6 and RG11 for HD.
Where it should not be used
Satellite IF, MoCA and DOCSIS 3.1 all push energy into the 1 to 2 GHz band, where RG59 fails on loss and on shield integrity. Long HD-SDI runs, rooftop antenna feeds with splitters, and any run that passes near mains cabling should use RG6 with a foil plus braid shield. If the existing installation is RG59 and the service has moved to a higher band, replacing the cable is usually cheaper than diagnosing intermittent dropouts, and the RG6 vs RG59 comparison quantifies the difference.
At the ends, use the right connector for the impedance and for the environment: an F connector for satellite and cable, a BNC for video equipment, and a compression fitting rather than a twist-on for anything outdoors. The RG6 cables overview covers the thicker alternative, and the coaxial connectors and adapters page covers impedance-safe transitions between them.
Practical scenarios
- Eight analogue cameras on a 24-port DVR: RG59 with compression BNCs is adequate for runs under 50 m, but power the cameras separately rather than over the coax.
- Cable modem relocation: do not extend with RG59; use RG6 and a quality splitter, because upstream DOCSIS channels occupy the band where RG59 is weakest.
- Subwoofer 12 m from the amplifier: RG59 with RCA ends works well and shields better than a thin audio lead, as long as the shield is bonded at both ends.
- Existing wall of RG59 and a new 4K camera: test one run end to end with a signal generator before committing, since 4K over coax usually means a proprietary extension standard with its own distance limit.
FAQ
Can RG59 carry HD television signals?
It can carry a single HD channel over short runs, because the modulation sits below 1 GHz and the receiver tolerates several dB of loss. It struggles with wideband services that stack many channels and upstream traffic into the same cable. For a modern multi-service installation, RG6 is the minimum.
Does RG59 work for internet over coax?
At short lengths, yes, but the upstream band and the higher downstream channels are exactly where its loss and shield leakage are worst. Intermittent drops that correlate with weather or with a neighbour’s service usually trace back to an RG59 drop. Replace the drop before replacing the modem.
Is copper-clad steel a problem?
For video and low-frequency signals, no: at those frequencies current flows in the outer layer of the conductor anyway. For DC power over coax, copper-clad steel has more resistance than solid copper, so a camera powered over a long RG59 run will see a voltage drop. Power the device locally or use a copper centre conductor.
