How to deliver 4G connectivity underground where the mobile coverage is zero.
4G connectivity underground is essential when installing a TCG120-4 or TCG140-4 at the bottom of a deep shaft, pit, or bunker. In such installations, you often face a critical challenge:
the 4G signal does not reach 50 meters underground.
Concrete, steel and depth block mobile networks almost entirely. But the nearest cell tower usually has clean coverage on the surface – you simply need a way to “bring” that signal down to the TCG device.
In practice, there are two reliable engineering approaches:
Option 1: Using a Coaxial Cable (Passive Solution)
Running an antenna cable from the surface to the TCG unit is the simplest and most robust solution – but only if the correct cable type is used.
At 50 meters, cable choice determines whether the connection works or fails.
- RG-58 / RG-174 / RG-316 – NOT recommended
These common cables are only suitable for short distances.
- Signal loss over 50 m: 30-40 dB
- Essentially unusable for LTE/4G/5G
- The device may fail to register on the network
Even though these cables fit SMA connectors, they must not be used for long underground runs.
- LMR-240 (RF-240) – Minimum acceptable
A mid-range cable, usable only with strong outdoor signal.
- Loss @ 1800 MHz: ~10.5 dB / 50 m
- Loss @ 2600 MHz: ~13-14 dB / 50 m
- Works only if the antenna receives a clean, strong signal
It can work, but it is borderline at higher LTE bands.
- LMR-400 (RF-400) – Recommended for 50-meter shafts
This is the standard coaxial cable for long-distance runs.
- Loss @ 1800 MHz: ~5.5 dB / 50 m
- Loss @ 2600 MHz: ~7 dB / 50 m
- Works perfectly with SMA connectors
- Excellent balance between performance and cable diameter
Combined with a high-gain outdoor antenna, LMR-400 offers stable, low-loss connectivity to a TCG1xx-4 installed deep underground.
Option 2: Using a 4G Repeater (Active Solution)
Instead of pushing the outdoor signal 50 meters down through cable attenuation, you can create a small “indoor cell” inside the bunker.
A typical repeater installation looks like this:
- Outdoor antenna on the surface, aimed at the nearest cell tower
- Cellular repeater installed at the top of the bunker
- Indoor antenna from the repeater radiating signal downward toward the TCG device
This solution bypasses cable losses entirely by regenerating and re-broadcasting the mobile signal.
When a repeater is the better choice
- When running thick low-loss cable is physically difficult
- When the shaft has sharp bends or obstacles
- When multiple devices need underground coverage
- When future upgrades must be easy (e.g., replacing devices without rewiring)
A properly installed repeater often provides the most stable 4G connectivity underground.
Which Option Should You Choose?
✔ Choose Option 1 (LMR-400 cable) when:
- You prefer a passive, maintenance-free installation
- Only a single TCG unit needs a signal
- The path is straight and allows a thick cable to be pulled
✔ Choose Option 2 (4G repeater) when:
- Installation space is limited
- The cable path is long or complex
- Multiple devices need coverage
- You want flexibility and easy expansion
Both options deliver reliable 4G connectivity for TCG devices in deep bunkers – the right choice depends on the site conditions.
If you need help selecting a cable, antenna or repeater model, Teracom can assist with RF planning and hardware specifications.