Before this:Antennas for scanning
Feedlines, connectors & grounding
Key takeaways Between the antenna and the receiver sits the feedline, and it quietly costs you signal. Coax loss grows with frequency and length, so keep runs short and use low-loss cable for the length you need. Every connector and adapter (SMA, BNC, N, PL-259) adds a little loss — don’t build adapter towers. And any outdoor antenna must be grounded, with a lightning arrestor, for safety — this is the one place in the hobby where getting it wrong is dangerous, so follow local code.
The last lesson got a good antenna up high. Now the signal has to travel down to your receiver without leaking away — and the antenna has to be safe up there. This lesson covers the plumbing: coax, connectors, and grounding. None of it is glamorous, and all of it can undo the work you just did on the antenna if you get it wrong.
Coax loss: the tax on every metre
The cable that carries your signal from the antenna to the receiver is coaxial cable — coax — and it is not lossless. Every metre absorbs a fraction of a decibel, and two things make that worse:
- Higher frequency. Coax loss climbs with frequency. The same cable that barely touches a VHF signal can eat a serious chunk of an 800 MHz one.
- Longer runs. Loss accumulates with length. A short jumper is nearly free; a long run up to a rooftop antenna is where it bites.
The two combine into the practical rule: the higher your band and the longer your run, the more the cable matters. A long, thin, cheap coax at UHF can throw away much of the signal your good antenna just captured — the classic way a strong antenna is quietly wasted.
Choosing and running coax
You do not need exotic cable, just the right cable for the job:
- Keep runs short. The cheapest loss reduction is fewer metres. Mount the receiver (or an SDR) as close to the antenna as practical, and don’t coil up excess cable “just in case.”
- Match the cable to the length. For a short desk jumper, thin flexible coax is fine. For a long rooftop run, step up to a proper low-loss coax — the extra cost buys back decibels you would otherwise lose every second.
- Weatherproof outdoor connections. Water in coax is ruinous. Seal outdoor connectors against the weather so the cable doesn’t slowly fill and rot.
- Mind the bends. Sharp kinks damage coax and change its behaviour; keep bends gentle.
Think of it as a budget: you spent effort getting signal onto the antenna, and the coax is where you can either preserve it or throw it away.
Connectors you’ll meet
The cable ends in connectors, and the scanning world uses a handful. You met these in Antennas 101; here they are with where each turns up:
| Connector | Where you’ll see it |
|---|---|
| SMA | Most RTL-SDR dongles and small antennas |
| MCX | Some SDR dongles |
| BNC | Handheld scanners, lab gear — quick twist-lock |
| N | Larger outdoor antennas and low-loss runs |
| PL-259 / SO-239 (UHF) | Common on scanner antennas and mounts |
The practical point is that your antenna and your receiver often don’t share a connector, so you will need an adapter — SMA-to-BNC, N-to-SMA, and so on.
Every connection is a small tax
Each connector and each adapter introduces a small loss and a tiny impedance bump, and — crucially — the effect stacks. A tower of three adapters chaining SMA to BNC to N to PL-259 adds up to a measurable loss and, worse, several extra points that can loosen, corrode, or fail. The habits that keep this in check:
- Use the right single connector where you can, rather than adapting through several.
- Keep adapter stacks short — one adapter is fine, a tower of four is asking for trouble.
- Keep every connection clean and tight. A loose or corroded connector is intermittent signal and maddening noise.
None of this is dramatic on its own, but combined with a long lossy coax it is exactly how a good antenna ends up sounding mediocre.
Grounding and lightning: the safety part
Everything above is about signal. Grounding is about safety, and it is not optional for an outdoor antenna. A metal antenna up high does two dangerous things: it accumulates static charge from the atmosphere, and it presents an attractive path for a nearby lightning strike. Without a proper ground, both look for a route to earth — and that route can be through your coax, your receiver, and your house wiring.
The essentials, done to local electrical code:
- Ground the antenna mast and system to a proper earth ground, so static bleeds off harmlessly instead of building up.
- Fit a lightning arrestor in the coax line where it enters the building, bonded to ground, to divert surge energy away from your equipment.
- Disconnect during storms. Even with protection, unplugging the antenna during an electrical storm is cheap insurance for your gear.
- When in doubt, get it done properly. This is the one area of the hobby where a mistake risks your equipment, your home, and your safety — not just a weak signal.
Grounding earns no better reception, but it is what makes an outdoor antenna a safe, long-term part of your station rather than a liability. With the antenna up, fed, and grounded, the next step is assembling it all into a working station.
Quick check: where does coax feedline loss hurt the most?
Recap
- Coax loss grows with frequency and length — it bites hardest on long runs at high bands, and can quietly undo a good antenna.
- Keep runs short, use low-loss coax for the length you need, weatherproof outdoor connections, and avoid sharp bends.
- Learn the connectors (SMA, MCX, BNC, N, PL-259) and expect to need an adapter to join antenna to receiver.
- Every connector and adapter adds a small loss that stacks — use the right single connector, keep adapter towers short, keep connections clean and tight.
- Ground any outdoor antenna and fit a lightning arrestor for safety — follow local code, disconnect in storms, and get it done properly if unsure.
Next up: Setting up your station.
Frequently asked questions
Does coax type really matter for receiving?
Yes, more than people expect, and more at higher frequencies and longer runs. Cheap thin coax can lose a large fraction of your signal over a long run at UHF, undoing a good antenna. For a short desk jumper it barely matters; for a run up to a rooftop antenna, better low-loss coax is worth it. Keep runs as short as practical and use quality cable for the length you do need.
Why do connectors and adapters cost signal?
Every connector and every adapter introduces a small loss and a small impedance discontinuity, and stacking several adapters multiplies the effect. A tower of SMA-to-BNC-to-N adapters can quietly eat a meaningful fraction of a decibel and add failure points. Use the right single connector where you can, keep adapter stacks short, and make sure each connection is clean and tight.
Do I need to ground an outdoor antenna?
If your antenna is outdoors, especially up high, grounding is a safety matter, not an optional upgrade. A proper ground and a lightning arrestor bleed off static build-up and give a nearby strike a path to earth other than through your equipment and home. Follow local electrical codes and, if unsure, have it done properly — this is the one part of the hobby where getting it wrong is dangerous.