HD over Coax with Baluns
Purpose
This document explains what baluns are, how they work, and when to use them. Baluns allow HD-TVI video signals (normally carried on coax) to travel over Cat5/6 twisted-pair cable instead — useful when existing Cat5/6 is already in place, or when Cat5/6 is easier to run than coax in a given building.
What Is a Balun?
A balun (short for Balanced-Unbalanced converter) is a passive adapter that converts a coaxial (unbalanced) video signal to run over a twisted pair (balanced) cable, and back again at the other end.
In CCTV, baluns let you use Cat5/6 cable in place of coax for HD-TVI cameras and DVRs. You fit one balun at the camera end (on the camera's BNC output) and one at the DVR end (on the DVR's BNC input). The HD-TVI signal travels between them over a single twisted pair within the Cat5/6 cable.
Why Use Baluns?
Existing cable infrastructure — the most common reason. A building already has Cat5/6 installed from a previous IT, phone, or IP CCTV system. Rather than pulling new coax, you reuse the existing cable with baluns.
Easier cable routing — Cat5/6 is thinner, lighter, and more flexible than coax. In tight conduit or where cable tray already carries Cat5/6, it can be more practical.
Longer runs — active baluns (with signal boosting) can extend HD-TVI runs beyond normal coax limits.
Passive vs Active Baluns
Passive Baluns
Passive baluns contain no electronics — a simple transformer that converts between balanced and unbalanced. No power required.
Suitable for: Up to approximately 200–300m on Cat5/6 at 5MP resolution.
Limitations: No amplification — signal degrades over longer runs.
Typical use: Any standard analogue install using Cat5/6 in place of coax within range.
Active Baluns
Active baluns contain amplification circuitry. They require a 12V DC power supply at the transmitter (camera) end.
Suitable for: Runs up to 400–600m on Cat5/6.
Limitations: Require power — additional PSU at the camera end; more expensive; PSU is an extra failure point.
Typical use: Large commercial installs, warehouse environments, runs too long for passive baluns.
Wiring Baluns
Each balun has two connections:
- BNC — connects to the camera or DVR BNC port
- Screw terminals — connects to the Cat5/6 twisted pair
A single Cat5/6 cable contains four twisted pairs. For a single camera channel, you only need one twisted pair. This means a single Cat5/6 cable can carry up to four camera channels simultaneously — one per pair.
Standard pair allocation
| Channel | Pair | Colours |
|---|---|---|
| 1 | Pair 1 | Blue / Blue-White |
| 2 | Pair 2 | Orange / Orange-White |
| 3 | Pair 3 | Green / Green-White |
| 4 | Pair 4 | Brown / Brown-White |
Always use both wires of the same twisted pair for a single channel — never mix wires from different pairs. Pairing is what gives the balanced signal its noise rejection. Mixing pairs is the most common balun fault.
Connection at each end
- Connect the balun's BNC to the camera BNC (camera end) or DVR BNC (DVR end)
- Connect the twisted pair wires to the balun's screw terminals — check polarity on the label
- Repeat at the other end using the same pair
Power Over Balun
Standard passive baluns carry video only — cameras need power separately.
Options:
- 12V DC adaptor locally at each camera
- Spare pairs in the Cat5/6 can carry 12V DC — use one pair for positive, one pair for negative
- Dedicated power cable alongside the Cat5/6
Carrying 12V on Cat5/6 pairs is acceptable for CCTV cameras (typically 300–800mA draw), but calculate voltage drop over the run length. For runs over 50m, measure voltage at the camera end under load before assuming it will be sufficient.
When to Use Baluns vs Coax vs IP
| Scenario | Recommended approach |
|---|---|
| New residential install, standard runs | RG59 coax with POC |
| Existing Cat5/6 already in place | Passive baluns on the existing cable |
| Long runs (> 300m) needed | Active baluns on Cat5/6 |
| High camera count, commercial | IP cameras on Cat5/6 with PoE switch and NVR |
| Tight conduit, coax won't fit | Cat5/6 with passive baluns |
| Upgrading an old structured-cable building to CCTV | Baluns — reuse the infrastructure |
Common Faults and Causes
| Fault | Likely cause |
|---|---|
| No image | Balun not connected to correct pair at one or both ends; BNC not seated |
| Noisy / patterned image | Wrong pair used — wires from two different pairs mixed together |
| Image on some channels but not others | One or more pairs in the Cat5/6 damaged or broken |
| Poor performance on long run | Using passive baluns beyond their range — switch to active |
| Hum bars / interference | Earth loop between camera and DVR; or cable running alongside high-current mains |
| All four channels on one cable affected | Cable fault — test the Cat5/6 with a cable tester |