Coax to Coax: Joining Without Losing Signal
Quick answer / TL;DR: Short answer: a barrel coupler joins two coax cables with about 0.1 to 0.3 dB loss per joint. One joint is acceptable, three is a planning failure. Support the joint, weatherproof it outdoors, and prefer a longer cable where possible.
Three coaxial families: BNC for CCTV, F-type for TV, N for RF – each with its impedance.Joining two coaxial cables uses a barrel coupler, an F-to-F adapter with no cable in between. Each joint adds a small loss and a large reliability risk.
The question is not whether a joint works, but how many are acceptable.
What a Joint Costs
| Element | Typical loss | Risk |
|---|
| F barrel | 0.1 to 0.3 dB | Centre pin misalignment |
| Poorly fitted connector | 0.5 dB and up | Ingress |
| Three joints in series | 1 dB | Cumulative |
A single joint is acceptable. Three in a row is a symptom of a poorly planned installation rather than a design.
Practice
- Use one joint only where unavoidable
- Prefer a longer cable
- Weatherproof outdoor joints
- Check the centre conductor is straight
- Support the joint so it carries no load
Support matters because a hanging joint flexes and eventually works the centre conductor loose.
Real-World Applications
Extending a feed to a relocated television may need one barrel and works fine. A wall plate feeding a splitter, then a barrel, then a second splitter is the pattern that produces intermittent dropouts on satellite.
Standards and Verification
| Reference | Relevance |
|---|
| IEC 61169 | RF connectors |
| SCTE | Distribution practice |
| IEC 61196 | Coaxial cable |
Insertion loss for a specific coupler is not provided in the knowledge base. Check the datasheet for marginal links.
Practical Notes
Count joints when diagnosing a weak signal. They are invisible on a drawing and numerous in reality.
Related reading: coax cable — blogs/news/coax-cable
Related reading: subwoofer coax cable — blogs/news/subwoofer-coax-cable
Related reading: hardline coax — blogs/news/hardline-coax
Frequently Asked Questions
Is one coupler acceptable?
Yes, with a small loss.
How many is too many?
More than one or two is a planning problem.
Do outdoor joints need sealing?
Yes, always.
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