Cellular Signal, your SIM and your Router: Signal Strength, Stability & Performance Explained

When selecting a SIM card for your cellular router, the right choice ensures fast, stable, and reliable connectivity for homes, businesses, and mobile setups. However, a strong signal alone doesn’t guarantee high performance – factors such as network congestion, signal-to-noise ratio (SNR), and even physical interference (such as Faraday cage effects) play a critical role.

This guide explains what really matters when choosing a SIM for a cellular router and how to maximise your network performance.

Signal Strength vs. Signal Quality: Why Bars Aren’t Enough

Most people assume strong signal bars mean better performance, but that’s only part of the story. Cellular routers rely on both signal strength and signal quality (Amongst other things) to ensure fast and stable connections.

Why Signal Strength Alone Isn’t Enough

• Interference & Noise: High-strength signals can still be affected by electromagnetic interference from other devices, degrading performance.
• Network Congestion: A strong signal in a crowded area doesn’t mean fast speeds—too many users sharing the same cell tower can slow you down.
• Reflections & Multi-Path Distortion: Signals bouncing off buildings or walls can introduce errors in data transmission.

Takeaway: Don’t just focus on signal bars—measure actual performance using metrics like Signal-to-Noise Ratio (SNR) and Reference Signal Received Quality (RSRQ).

Signal-to-Noise Ratio (SNR): The Hidden Factor in Router Performance

Your cellular router’s throughput (speed and stability) is directly impacted by SNR, a crucial but often overlooked factor.

What is Signal-to-Noise Ratio (SNR)?

• SNR measures the difference between the actual cellular signal and background noise.
• A high SNR means a clear, strong signal with minimal interference.
• A low SNR means excessive noise, leading to slower speeds, dropped connections, and packet loss.

How to Improve SNR in a Cellular Router:

• One of the obvious solutions is to use an External Antenna: Directional antennas can help eliminate noise by focusing on the strongest signal source.
• Position Your Router Carefully: Avoid placing the router near electronic devices, which generate electromagnetic interference (e.g., microwaves, power cables). You’d be surprised how often this is overlooked, with people trying to hide the ‘unsightly’ router away, forgetting that they may inadvertently be blocking the signal path to thee device.
• Check Tower Distance: If your router constantly switches between towers, SNR can fluctuate. Locking onto a stable frequency band can help.

Takeaway: SNR is as important as signal strength—focus on getting a strong AND clean signal for optimal router performance.

The Faraday Cage Effect: Why Buildings Kill Signal Quality

Have you ever noticed bad cellular reception indoors, even when outdoor signal is strong? That’s due to something called the Faraday Cage Effect—when building materials block or weaken radio signals.

How Does a Faraday Cage Effect Cellular Routers?

• Metal structures (steel frames, reinforced concrete, aluminium siding) reflect or absorb cellular signals.
• Low-emissivity (Low-E) glass can block radio signals, making it hard for a router to pick up an outdoor tower.
• Underground rooms (basements, parking garages) suffer from complete signal loss due to thick concrete layers.

How to Overcome the Faraday Cage Effect?

• Again, if possible use an External Antenna: A rooftop or window-mounted antenna can bypass indoor interference.
• Relocate the Router: Position it near a window or external wall to reduce signal loss (still not ideal).
• Consider a Signal Repeater: A cellular signal booster can help rebroadcast signals inside the building. Beware of cheap options that aren’t approved by Ofcom, there are a lot out there that can render your deployment illegal. Only buy from a trusted source. These are not cheap to buy.

Takeaway: If your router is inside a building with thick walls, use external antennas or approved boosters to prevent signal loss.

Network Congestion: The Bottleneck You Can’t See

Even with perfect signal conditions, your router can still experience slow speeds and high latency due to congestion.

What Causes Network Congestion?

• Too many users on a single cell tower (common in urban areas and apartment buildings). Currently cellular communications are contended (shared), with the introduction of 5G SA (Standalone), it will be possible to utilise an uncontended cellular service. This will come at a price and may, in time replace some leased line deployments.
• Heavy bandwidth consumption (e.g., streaming services, gaming, video conferencing).
• Network de-prioritisation—some SIMs (especially MVNOs) are assigned lower priority than direct carrier customers. It is often very difficult to establish if this is the case.

How to Reduce Congestion Issues on a Cellular Router?

• Use a specific IoT SIM: It is true that private APNs and IoT SIMs have a slightly different priority over regular MBB SIMs, however, it may well be the case that the difference is negligible, especially in heavily contended areas (events / stadiums and so on) where the tower may not have enough capacity to offer the usual quality of service.
• Change Bands/Carriers: Some towers may be overloaded—manually switching frequency bands can improve performance. Only really recommended to be done by experienced users.
• Monitor Peak Hours: If possible, schedule large downloads/uploads during off-peak times. Not always easy to do.

Takeaway: Network congestion can reduce speeds even with strong signal—consider IoT SIMs for better priority access (although don’t bank on it).

Frequency Bands: Why Compatibility Matters

Unlike smartphones, advanced cellular routers rely on multiple frequency bands to deliver stable Internet. Different bands perform better in different scenarios. In some scenarios, cellular routers utilise something called Carrier Aggregation to deliver the service and speeds required. This is where multiple bands from different towers are used together.

Which Frequency Bands Matter?

• Low Bands (700MHz, 800MHz, 900MHz): Best for long-range connectivity and better indoor penetration (but slower speeds).
• Mid Bands (1800MHz, 2100MHz): Balance between speed and coverage—good for most urban/rural users.
• High Bands (2600MHz, 3500MHz, 5G mmWave): Offer fast speeds but require line-of-sight and struggle with building penetration.

How to Choose the Right Bands for Your Router?

• Check Carrier Bands: Ensure your router supports the carrier’s frequency bands.
• Use Band Locking: If your router allows it, manually lock onto the best-performing band for consistent speeds.

Takeaway: Routers perform best when using the right frequency band—low bands for coverage, high bands for speed.

Latency: The Overlooked Performance Killer

Latency (ping) affects real-time applications like video calls, gaming, and remote work. Even with good speeds, high latency can ruin the experience.

What Increases Latency?

• Poor SNR (too much noise in the signal).
• Network congestion (competing users).
• Long-distance data routing (choosing a far-away tower or server).

How to Reduce Latency for a Cellular Router?

• Improve SNR: A clean signal reduces retransmissions, lowering latency.
• Use a Wired Connection: If possible, connect devices via Ethernet instead of Wi-Fi for lower ping.
• Choose the Right Carrier: Some networks prioritise low-latency routing better than others. The information around this isn’t something that is immediately available to everyday users.

Takeaway: Low latency is critical for real-time apps—optimise SNR and reduce congestion for best results.

Fun Facts & Common Mistakes

Fun Fact: Did you know that 5G’s high-speed millimetre-wave (mmWave) bands can be blocked by rain, glass, and even leaves? That’s why most 5G routers still rely on low and mid-band LTE for stable performance.

Common Mistakes When Choosing a SIM for a Cellular Router:

• Focusing only on signal bars—SNR and network congestion matter just as much.
• Placing routers in signal-dead zones—like basements, metal-walled rooms, cupboards or buildings with thick concrete.
• Ignoring frequency bands—not all routers support all carrier frequencies.
• Using the wrong type of SIM—Mobile Broadband SIMs have very different traffic priorities to IoT specific SIMs.

Final Verdict: Get the Best SIM for Your Router

To get the best possible performance from your cellular router, focus on:

• Strong signal AND high SNR for clear reception.
• Avoiding Faraday cage effects inside buildings.
• Using the right frequency bands for your location.
• Reducing latency for real-time applications.

With these tips, you’ll maximise speed, stability, and reliability for your cellular router setup. Talk to our experienced Sales Team today to find out more about our SIMs and routers.
Call 01234 865880 or email sales@comms365.com.