Simplex Channels: Radio Straight to Radio
On a simplex channel, your radio transmits and receives on the same frequency, and the signal travels directly from your aerial to the other radio. Nothing sits in between, no tower, no infrastructure, no third party relaying the call. It's the radio equivalent of shouting across a paddock: if the other person can see you, they can hear you.
That directness is a genuine strength. There's less to depend on, it's ideal for close work on a yard, a site or a job face, and it keeps local chatter off the wider area channel. A simplex channel also keeps working even if a repeater site nearby has gone offline for maintenance, which makes it a sensible fallback to keep programmed into every radio regardless of what else you're running.
Where Simplex Falls Over
The trade-off is range, and range on simplex depends heavily on terrain. Hills, buildings, stacks of shipping containers and heavy steel all block a simplex signal outright. Two radios can be a kilometre apart with a ridge between them and hear absolutely nothing, even though the straight-line distance is trivial.
- Handheld to handheld: roughly 1 to 3km on flat, open ground with clear line of sight
- Mobile to mobile: roughly 5 to 10km under the same conditions
- In built-up areas, gullies or bush, treat both figures as a fraction of that
Those figures are a guide only. Real coverage depends on terrain, aerial type and where the radio is actually sitting, not just the spec sheet.
Repeater Channels: Borrowing the Hilltop
A repeater is a radio installed at a high site, a hilltop, a tower, a tall building, that listens on one frequency and rebroadcasts what it hears on a second frequency, at the same instant and at far higher power than your handheld can manage. Your 5W radio only has to reach the hill. The hill does the hard work of reaching everyone else.
That single shift in geometry is what makes a repeater so effective. Instead of needing a direct line of sight to the other radio, you only need a clear path up to the repeater, and height beats power in most real-world situations. Two handhelds that can't hear each other directly can often still talk perfectly well through a repeater covering the same ground.
What a Repeater Channel Actually Buys You
- Far wider coverage, often across a whole site, valley or region
- Everyone on the channel hears the same call at the same time
- Radios with no direct path to each other can still talk via the repeater
What It Doesn't Fix
A repeater is a shared resource, so only one conversation runs at a time, and shadow areas still exist underneath it: deep gullies, basements, the inside of heavy steel structures. It's also a single point of dependency, site power, aerials and links all matter, and if the repeater itself goes down, everyone relying on it loses coverage at once. That's exactly why a working simplex channel is worth keeping programmed as a fallback, not a relic from before you had a repeater.
For the deeper technical picture, duplexers, DMR versus analogue, RSM licensing and which repeater actually suits a given site, see our guide on what a digital radio repeater does.
The One-Way Trap: Hearing Isn't the Same as Being Heard
This is the single most common radio complaint we hear that isn't actually a faulty-gear problem: "I can hear the base station perfectly, but they can't hear me." It's a real and predictable effect, not a coincidence.
A repeater transmits from a hilltop at high power, easily 25W or more, with a proper elevated aerial. A handheld answering it is doing the opposite: 5W, from ground level, often from inside a building or behind a vehicle. The downlink (repeater to you) is a much easier path than the uplink (you back to the repeater). So a handheld can often receive a strong, clear signal while its own reply never makes it back up the hill at all.
What Actually Fixes It
Moving to slightly higher ground, stepping out from behind a building or vehicle, or upgrading to a vehicle-mounted 25W unit with a proper roof aerial all improve the uplink specifically. None of these are exotic fixes. They're the same three things worth checking before assuming a radio itself has failed.
Handheld at 5W vs Mobile at 25W: What Actually Changes
Five times the transmit power sounds like it should mean five times the range. It doesn't. Radio signals spread out as they travel, so roughly four times the power is needed just to double the distance in clear air. Going from 5W to 25W is a genuine and useful lift, but on its own it's worth somewhere around double the range at best, and less than that once hills and buildings get involved.
The bigger difference is everything else that comes bundled with a proper mobile install, not the wattage figure on the spec sheet.
| Factor | Handheld (5W) | Mobile (25W) |
|---|---|---|
| Aerial height | Chest height, often indoors or shadowed | Roughly 2m, roof or bullbar mounted, clear of obstructions |
| Aerial quality | Short rubber aerial, close to the body | Proper tuned whip aerial with gain |
| Body effect | Standing between the radio and the repeater absorbs signal | Not a factor, aerial is external to the vehicle |
| Power source | Battery, output and run time fade through the shift | Vehicle supply, output stays consistent all shift |
| Best suited to | Staff on foot, close-in teamwork | Drivers, wide-area travel, anyone needing reliable reach |
A tuned aerial with proper gain, mounted 2m up and clear of the body, will often outperform a raw wattage increase on its own. Turning around, or stepping into the open, can genuinely fix a marginal call, because the body is a surprisingly effective radio-frequency absorber at close range.
Getting the Best Out of What You've Already Got
Most patchy-radio complaints on an existing fleet come down to a handful of habits and settings, not a hardware failure. Before assuming a radio needs replacing, work through these:
- Use the repeater channel for day-to-day traffic across the wider site or region
- Keep a simplex (talkaround) channel programmed on every radio, and actually use it for close-in work and as a fallback if the repeater is down or unreachable
- If a call won't go through, move: step out from behind the building, get to higher ground, or get clear of steel and machinery
- Hold the handheld upright, about 5cm from your mouth, with the aerial clear of your body
- Never transmit on a handheld with a damaged or missing aerial. It hurts performance and can genuinely damage the radio
- Treat aerials and mounting as the cheapest upgrade available. Poor aerial fitment undoes an otherwise good radio
If your site has genuine coverage gaps that channel discipline alone won't fix, our guide on digital radio repeaters covers when a repeater is the right call, and our radio licensing guide covers what's needed to run one legally in NZ.