When people use cellular connectivity with a Raspberry Pi, they often focus on the modem while giving little attention to antenna placement, which is a common mistake because in real deployments antenna position can matter more than the LTE category itself. When using a 4G LTE CAT IV HAT with a Raspberry Pi 4, antenna placement directly affects speed, stability, and overall reliability: a poor setup can severely reduce performance even in areas with strong network coverage, while a well-placed antenna can make weak signals usable. This blog explains how antenna placement influences the performance of a Raspberry Pi 4 with a CAT IV HAT, focusing on technical, practical considerations grounded in real-world signal behavior.

Why Antenna Placement Matters in LTE Systems

LTE works by sending radio signals between the modem and the cellular tower. These signals travel through air and obstacles. Along the way, they lose power and pick up interference.

The antenna acts as the gateway between the air and the modem. Its position decides:

• How much signal reaches the modem

• How much noise enters the system

• How stable the connection remains

Even small placement changes can cause large differences. Moving an antenna by 30 cm can raise or drop signal quality.In LTE systems, signal quality matters more than raw signal strength. Placement influences both.

How Raspberry Pi 4 Design Affects Antenna Behavior

The Raspberry Pi 4 is compact and electrically active. It contains:

1. Electrically noisy platform

The Raspberry Pi 4 is a compact but highly active electronic system, which means it naturally generates significant electromagnetic interference (EMI) during normal operation.

2. High-speed USB 3.0 interfaces

USB 3.0 operates at multi-gigabit speeds and is a well-known source of broadband noise that can interfere with nearby RF signals, especially cellular frequencies.

3. HDMI display outputs

The HDMI ports use high-frequency differential signaling, which can radiate noise and negatively affect antenna reception when antennas are placed too close.

4. Switching voltage regulators

The Pi 4 relies on switching power regulators that introduce high-frequency noise into the system, further degrading RF performance if not properly isolated.

5. High-frequency system clocks

Internal clocks running at high speeds generate harmonics that can couple into antenna paths, reducing signal-to-noise ratio.

All these generate electrical noise. When antennas sit close to these components, signal quality drops. A Raspberry Pi4 with CAT IV HAT often places antennas near the board. This makes placement even more important. External antennas usually perform better due to better isolation.

Signal Metrics Influenced by Antenna Placement

Antenna placement directly affects RSSI, RSRP, RSRQ, and SINR, influencing cellular signal strength, noise levels, link quality, throughput, stability, and overall network reliability. To understand performance changes, we need to look at LTE signal metrics.

1. RSSI: Total Received Power

RSSI measures the total received power at the antenna, including both the desired signal and background noise, so a higher RSSI value does not necessarily indicate better performance. Poor antenna placement can significantly degrade reception and, in some cases, reduce RSSI by as much as 10 dB. A 10 dB loss means signal power drops by about 90%.

2. RSRP: Useful Signal Power

RSRP measures the strength of the LTE reference signal, providing a clearer indication of cellular link quality than RSSI. Values better than −90 dBm indicate strong signal, while readings worse than −105 dBm are considered weak. Adjusting antenna placement can significantly improve RSRP, often boosting it by 6 to 12 dB and enhancing overall connection performance.

3. RSRQ: Signal Quality

RSRQ indicates the quality or “cleanliness” of the LTE signal, with low values signaling high interference. Poor RSRQ is often caused by nearby electronic components, while proper antenna placement can reduce noise pickup and improve overall signal quality.

4. SINR: Data Rate Driver

SINR determines the efficiency of modulation and coding in LTE, directly affecting data speeds. Values above 20 dB enable high-speed connections, while readings below 5 dB severely limit throughput. Proper antenna placement, especially indoors, can significantly improve SINR, often doubling it and enhancing overall network performance.

Physical Factors That Shape Antenna Performance

Antenna performance is influenced by placement, orientation, proximity to electronics, obstructions, grounding, and environmental reflections, all affecting signal strength, interference, stability, and overall cellular connectivity.

1. Distance From Obstacles

LTE signals weaken when passing through objects.

Typical losses:

• Dry wall: 3–5 dB

• Brick wall: 8–15 dB

• Concrete wall: 15–30 dB

Placing antennas near windows reduces this loss.

2. Height Above Ground

Higher antennas see fewer obstructions.

• Floor-level antennas collect reflections

• Elevated antennas receive cleaner paths

Raising antenna height by one meter can improve SINR by 3 to 6 dB.

3. Orientation and Polarization

Most LTE towers use vertical polarization.

Best practice:

• Keep antennas vertical

• Avoid flat placement

Wrong orientation can reduce received signal power by up to 50%.

Dual Antenna Placement and MIMO Performance

Dual antenna placement is critical for MIMO performance, as proper spacing and orientation maximize spatial diversity, reduce interference, improve signal quality, increase throughput, and enhance overall LTE reliability. Most CAT IV modems support two antennas for MIMO.

1. Antenna Separation

MIMO relies on signal diversity.

• Antennas too close capture similar signals

• Diversity drops when spacing is small

Recommended spacing:

• Minimum: 20 cm

• Ideal: 40–50 cm

Better spacing often improves throughput by 20–30%.

2. Antenna Angle

Slight angular separation helps.

Common setup:

• One antenna vertical

• One antenna tilted

This improves diversity in indoor environments.

Internal vs External Antenna Placement

Internal antennas are compact but prone to interference from nearby electronics, often reducing signal quality, while external antennas offer better isolation, stronger reception, and more reliable cellular performance.

1. Internal Antennas

Internal antennas are compact but limited.

Challenges include:

• Close proximity to noise

• Poor ground reference

• Limited orientation options

Internal antennas often lose 5–10 dB compared to external ones.

2. External Antennas

External antennas allow flexible placement.

Benefits include:

• Higher gain

• Better isolation

• Improved positioning

External antennas provide more stable performance in weak signal areas.

Directional and Omnidirectional Antennas

Directional antennas focus signals in a specific direction, providing higher gain and longer range, while omnidirectional antennas radiate evenly in all directions, offering broader coverage but lower peak performance.

1. Omnidirectional Antennas

These antennas receive signals from all directions.

Best for:

• Mobile setups

• Urban areas

• Unknown tower direction

Placement still matters for height and clearance.

2. Directional Antennas

Directional antennas focus energy.

Advantages:

• Higher signal strength

• Better SINR

Disadvantages:

• Require alignment

• Perform poorly if misaligned

They suit fixed installations.

Interference Sources Near Raspberry Pi 4

Several components generate interference.

1. Common sources:

• Power adapters

• USB 3.0 cables

• HDMI outputs

USB 3.0 noise often affects LTE bands.

2. Recommended spacing:

• 10 cm from cables

• 15 cm from power circuits

Moving antennas away from these sources improves RSRQ.

Heat and Antenna Placement

Heat increases electronic noise.

• High temperature raises noise floor

• Modem sensitivity drops

Avoid placing antennas near heatsinks. Allow airflow around the HAT.

Stable temperature improves long-term performance.

Indoor vs Outdoor Placement

1. Indoor Placement

Indoor environments introduce:

• Wall losses

• Multipath reflections

Best indoor practices:

• Place antennas near windows

• Keep them high

• Avoid metal objects

2. Outdoor Placement

Outdoor antennas provide large gains.

Typical improvements:

• RSRP: +8 to +15 dB

• SINR: +5 to +10 dB

Outdoor placement often transforms weak links into stable ones.

Data Rate Changes Caused by Placement

LTE Cat IV supports up to:

• 150 Mbps downlink

• 50 Mbps uplink

Real-world speeds depend on signal quality.

Observed results:

• Poor placement: 2–5 Mbps

• Improved placement: 10–25 Mbps

• Optimized placement: 30+ Mbps

Placement alone can produce 5× speed improvement.

Latency and Stability Impact

Poor placement increases:

• Packet retries

• Jitter

• Session drops

Latency often increases by 30–70 ms under noisy conditions. Good placement stabilizes round-trip times.

Common Antenna Placement Mistakes

Avoid these issues:

• Mounting antennas inside metal cases

• Placing antennas flat on desks

• Keeping dual antennas too close

• Running cables near RF paths

Each mistake reduces performance.

How to Optimize Antenna Placement

A simple process works well.

Step-by-step approach

1. Record baseline signal values

2. Move antenna location

3. Measure again

4. Compare SINR and RSRQ

5. Select best position

Focus on quality metrics, not RSSI alone.

Impact on Raspberry Pi 4 Projects

A well-placed antenna improves project reliability.

1. Remote Monitoring

Requires a stable uplink; even small packet loss can disrupt real-time data and compromise system reliability.

2. Video Streaming

Demands high SINR for smooth playback, and performance can degrade significantly when interference reduces signal quality.

3. Industrial Systems

Require consistent low latency, and even brief signal drops can cause system failures or disrupt automated processes.

Good antenna placement supports long-term operation.

Final Thoughts

Antenna placement is vital for a 4G LTE CAT IV HAT for Raspberry Pi 4, affecting signal strength, quality, speed, and reliability. Raising antennas, spacing them for MIMO, and keeping them away from noisy components like USB and HDMI improves SINR and performance. External antennas usually provide better results due to reduced interference. Proper placement ensures stable, high-speed cellular connectivity, making the Raspberry Pi 4 suitable for demanding applications.