The Anatomy of a Coaxial Cable
A coaxial cable has four concentric layers. At the center is a solid or stranded copper conductor — the actual signal-carrying wire. Surrounding it is a dielectric insulator, typically a foam or solid polyethylene material, that maintains a precise, consistent spacing between the center conductor and the next layer. Wrapped around the dielectric is the shield, which consists of one or more layers of braided copper wire, aluminum foil, or a combination of both. The entire assembly is then covered by a PVC or polyethylene outer jacket that protects against physical damage and moisture.
The term "coaxial" refers to the fact that all layers share the same geometric axis — they are literally co-axial, one inside the other. This concentric geometry is what gives coax its favorable electrical properties: the signal travels on the center conductor, and the shield acts as the return path and as a barrier that prevents external electromagnetic interference from entering the cable and prevents the signal from radiating outward.
Why Shielding Matters for Signal Quality
The shield is the most critical quality differentiator among coaxial cables. A cable with inadequate shielding is susceptible to ingress — external radio frequency interference from nearby electronics, LTE signals, or electrical noise entering the cable and corrupting the broadband signal. Ingress raises the noise floor on the cable, which reduces the signal-to-noise ratio (SNR) that your DOCSIS modem measures.
SNR directly determines how much data the modem can encode per symbol. A high SNR allows the modem to use high-order QAM modulation (QAM-4096 on DOCSIS 3.1), squeezing more bits per hertz of spectrum. When SNR drops due to poor shielding or connector problems, the modem falls back to lower-order modulation, reducing throughput even if the ISP's network is otherwise healthy. This is why replacing old coax with properly shielded RG-6 quad-shield cable often improves internet speeds without any other changes.
RG-6 vs RG-11: Which Cable Do You Need?
The two coaxial cable types you are likely to encounter for cable internet and TV are RG-6 and RG-11, both with a characteristic impedance of 75 ohms. The "RG" designation stands for "Radio Guide," a US military specification system that has carried over into civilian use.
RG-6 is the standard for residential cable installations. Its center conductor is approximately 18 AWG (1.02 mm diameter), and it attenuates signal at roughly 6 dB per 100 feet at 1 GHz. This level of loss is acceptable for the typical interior runs in a home, which rarely exceed 50–100 feet from the entry point to the modem. RG-6 quad-shield adds a second foil layer and a second braid layer on top of the standard dual-shield construction, dramatically improving shielding effectiveness.
RG-11 has a larger center conductor — approximately 7 AWG equivalent (1.63 mm diameter) — which reduces signal attenuation to about 1.5 dB per 100 feet at 1 GHz. This lower loss makes RG-11 the right choice for long runs, such as from the cable company's tap on the street to the entry point of your home, or for long interior runs that would cause excessive signal loss with RG-6. RG-11 is stiffer, heavier, and harder to route through walls and conduit, making it impractical for most interior applications.
F-Type Connectors and Why They Matter
The standard connector for residential coaxial cable is the F-type connector, a threaded fitting where the center conductor of the cable itself forms the pin. F-connectors are used everywhere cable TV and internet signals travel — on the back of your modem, cable boxes, wall plates, and splitters.
Connector quality and installation method significantly affect signal integrity. Crimp-type F-connectors are common but require a proper die and tool to achieve a secure, weatherproof crimp. Compression-type F-connectors create a more reliable mechanical and electrical connection and are preferred for quality installations. Push-on or "EZ" connectors are convenient but prone to intermittent contact, especially when cables are moved or flexed. Any connector with corrosion, damage, or improper installation can introduce signal loss or noise at that point in the cable path.
How Splitters Affect Your Internet Signal
A passive coax splitter divides the incoming signal between multiple output ports. Every split introduces insertion loss: a standard 2-way splitter reduces the signal level on each port by approximately 3.5 dB; a 3-way splitter loses about 5.5–7 dB per port; a 4-way splitter loses roughly 7–8 dB per port. These losses are cumulative — if you have a splitter feeding another splitter, the losses add together.
Your DOCSIS modem requires the received signal to be within a specific power range, typically -7 to +7 dBmV for downstream channels. Too much signal loss drops the receive level below the acceptable range, causing the modem to struggle to lock channels. Too much signal (caused by an amplifier that is overdriving the input) can also degrade performance. The goal is to use the minimum number of quality splitters necessary and ensure the signal level at the modem's input is within spec.
Checking Coax Quality Through Modem Diagnostics
Most DOCSIS modems expose a diagnostic page, usually accessible at 192.168.100.1 in your browser. This page shows downstream received power levels, upstream transmit power levels, SNR for each bonded channel, and uncorrectable error counts. These values give you a real-time view of your coax plant health without any special equipment.
Downstream power should be between approximately -7 and +7 dBmV for DOCSIS 3.0. Downstream SNR should be 33 dB or higher for reliable QAM-256 operation. If your modem shows signal levels outside these ranges or high uncorrectable error counts, the coaxial signal path from the street tap to your modem has a problem — degraded cable, corroded connectors, or too many splitters are the most common causes.
When to Replace Your Coaxial Cable
Old coaxial cable — particularly RG-59, which was the standard before RG-6 and has higher loss and poorer shielding — should be replaced if you are experiencing persistent slow speeds, frequent modem disconnections, or poor signal levels in the modem diagnostics. RG-59 is identifiable by its thinner profile and older-style cable markings. Homes wired in the 1980s or early 1990s often still have RG-59 throughout.
Even with RG-6, damaged cable that has been kinked, pinched in a door, or exposed to moisture penetrating through cracked connectors should be replaced. Water in the coax insulation dramatically increases signal loss and creates noise. A visual inspection of all visible cable runs, wall plates, and connectors — looking for corrosion (green or white oxidation on the center conductor or connector threads), cracked jacket, sharp bends, and loose connectors — can identify obvious problems before you dig into modem diagnostics.
RG-6 vs RG-11 Comparison
| Feature | RG-6 | RG-11 |
|---|---|---|
| Impedance | 75 ohm | 75 ohm |
| Typical use | Interior home wiring, modem connections | Long exterior runs, street tap to home |
| Attenuation at 1 GHz | ~6 dB per 100 ft | ~1.5 dB per 100 ft |
| Max recommended length | ~150 ft interior | ~300 ft exterior |
| Connector type | F-type | F-type |
Frequently Asked Questions
Does coaxial cable quality affect internet speed?
Yes, significantly. Damaged, corroded, or low-quality coaxial cable introduces signal loss and noise that degrades the signal-to-noise ratio your modem receives. A low SNR forces the modem to use lower-order modulation — sending fewer bits per symbol — which directly reduces throughput. Old RG-59 cable, loose F-connectors, excessive splitters, or water-damaged cable are common causes of slow speeds and frequent disconnections even when the ISP's network is otherwise healthy. Checking your modem's signal diagnostics page can confirm whether coax quality is affecting your connection.
What is the difference between RG-6 and RG-11?
RG-6 and RG-11 are both 75-ohm coaxial cables, but they differ in conductor size and attenuation. RG-11 has a larger center conductor (approximately 1.63 mm vs 1.02 mm for RG-6), which means it loses less signal per foot — roughly 1.5 dB per 100 feet at 1 GHz versus about 6 dB per 100 feet for RG-6. This makes RG-11 better for long runs (over 150 feet) between the street tap and your home. RG-6 is the standard for typical interior home wiring runs under 150 feet. RG-11 is stiffer and harder to work with, making it impractical for most indoor installations.
How does a coax splitter affect internet speed?
Every passive coaxial splitter reduces the signal level on each output port. A standard 2-way splitter introduces approximately 3.5 dB of loss per port; a 3-way splitter loses about 5.5–7 dB. Each decibel of signal loss reduces the SNR your modem sees. While a single quality splitter in a clean installation is usually tolerable, daisy-chaining multiple splitters or using cheap splitters with poor isolation can push your modem's receive level below the acceptable range, causing uncorrectable errors, dropped packets, and reduced speeds.
What type of coaxial cable do I need for cable internet?
For cable internet, you need RG-6 quad-shield coaxial cable rated to at least 1 GHz — and ideally to 3 GHz if you want full DOCSIS 3.1 compatibility. RG-6 is the current standard for residential cable drops. Avoid RG-59, which is an older, thinner cable with much higher signal loss and poor shielding that was designed for analog TV and is inadequate for modern broadband. All connectors should be properly crimped or compression-type F-connectors; push-on connectors are unreliable and often introduce intermittent signal problems.
How do I know if my coaxial cable is causing internet problems?
Log in to your cable modem's diagnostic page (typically at 192.168.100.1) and check the downstream signal levels, upstream power levels, and SNR. DOCSIS 3.0 downstream power should be between -7 and +7 dBmV; SNR should be above 33 dB. If values are outside these ranges, the coax signal path from the street to your modem is likely degraded. Common culprits are corroded connectors, damaged cable shielding, excessive splitters, or old RG-59 wiring. You can also look for high uncorrectable error counts in the modem's event log.
Can I use the same coaxial cable for TV and internet?
Yes, cable TV and cable internet share the same coaxial infrastructure in your home by design. The cable signal entering your home contains both TV channels and DOCSIS internet data carried in separate frequency bands. A splitter divides the incoming signal to feed both a cable box and a modem from the same coax drop. However, each split reduces signal level, so using many splitters or low-quality splitters to feed many devices can degrade both TV and internet quality. For best results, minimize the number of splits and use quality RG-6 cable throughout.