“Aligning a point-to-point antenna is not just about chasing signal strength, it is about tuning into clarity, stability, and precision. In RF engineering, a well-peaked antenna is the difference between connectivity and chaos.” – MJ Martin
Antennas come in all shapes and sizes. The first image is of 896 IoT radios, all sharing the same space and each having its own antenna. They form organically into a mesh topology. They manage all of the problems and issues of the close proximity all by themselves. There is no need for the operator to make any manual alignment for corrections to these thousands of mesh connections as they self-align. It is like magic. These tiny radios are very smart and form their own network easily and quickly.
Unfortunately, most other antennas are not as smart and they need to be manually aligned for optimum performance. So, this article discusses what measurements need to be captured when peaking a traditional antenna within a 1:1 radio link.
When aligning a point-to-point antenna link on a tower, precise measurements are critical to ensuring optimal performance of the wireless link.
The process, commonly referred to as “peaking” the antenna, involves fine-tuning its direction to maximize signal strength and link quality.
Signal Strength
The most fundamental parameter to monitor during this process is the Received Signal Strength Indicator (RSSI), which reflects the power level of the received signal. RSSI is expressed in negative decibels (dBm), with values closer to zero indicating stronger signals, for example, an RSSI of –45 dBm is significantly better than -70 dBm. However, strong RSSI alone is not sufficient to guarantee link reliability.
In radio communication, signal strength refers to the power of a received radio signal at a specific location, typically the receiver’s antenna. It is a measure of how strong or weak the radio wave is when it arrives at the receiving device. Signal strength is crucial for reliable communication, as a stronger signal generally results in a clearer and more stable connection.
Signal-to-Noise Ratio
Equally important is the Signal-to-Noise Ratio (SNR), which measures the difference between the signal level and the background RF noise. A higher SNR denotes a cleaner, more distinguishable signal, free from interference.
Typically, an SNR greater than 20 dB is considered acceptable, while values exceeding 30 dB are indicative of excellent link conditions. A high RSSI paired with a low SNR often suggests nearby RF interference, making it critical to evaluate both metrics in tandem.
Signal-to-noise ratio (SNR) is crucial because it determines the quality and reliability of the transmitted data. A higher SNR means the desired signal is stronger than the background noise, leading to clearer and more reliable communication. Conversely, a low SNR can result in data corruption, retransmissions, and degraded performance.
How do you Read Me?
In the old Hollywood war movies, the radio operators would ask, “How do you read me?” and the classic response in the older analog days was typically, “I read you loud and clear.” Sometimes they might reply, “I read you 5 by 5.” The ‘loud” or the first “5” was the RSSI or signal level and the “clear” and the second “5” was the SNR, which separated the voice from the static. So not much has actually changed in the digital realm as the link still needs to be “loud and clear” or “5 by 5”.
See another related article specifically discussing the noise floor. Use this link to read it.
Modulation Rate
In addition to signal strength and clarity, peaking efforts must account for the link’s modulation rate or quality, which defines the highest modulation and coding scheme the radios can sustain. This parameter directly influences data throughput, with higher modulation levels (such as QAM256) enabling greater bandwidth efficiency. In QAM256, each symbol carries 8 bits of data. This means that for each symbol transmitted, 8 bits of information are encoded. Therefore, the spectral efficiency of QAM256 is 8 bits per hertz. QAM256 is a type of high order modulation and it extremely sensitive to errors. Whereas, a lower order modulation such as BPSK (Quadrature Phase Shift Keying) is just 1 bit per hertz and is therefore easier to work with and very tolerant of any problems. In Binary Phase-Shift Keying (BPSK) modulation, the spectral efficiency is 1 bit per hertz (1 bit/Hz). This means that for every 1 Hz of bandwidth used, 1 bit of information can be transmitted. This is because BPSK uses two distinct phases to represent binary data, effectively encoding one bit of information per symbol.
Any degradation in the high order modulation rate can signal alignment issues (antennas not actually pointing directly at each other), environmental interference (trees or buildings obstructing the path), or equipment mismatch (such as a 75 ohm connection when a 50 ohm cable is needed).
Bit Error Rate
Alongside the modulation rate are the Bit Error Rate (BER) and Packet Error Rate (PER) which offer valuable insight into the link’s stability. Elevated error rates can result from poor alignment or RF noise and must be minimized to maintain consistent communication.
Bit Error Rate (BER) is a performance metric that quantifies the number of bit errors that occur during data transmission, relative to the total number of bits transmitted. It is a ratio (or, less commonly, a probability) of incorrectly received bits to the total number of bits sent. Essentially, it measures the reliability of a digital communication link.
In the case of Packet Error Rate (PER), it is represented as the ratio of incorrectly received data packets to the total number of packets transmitted, often expressed as a percentage or fraction.
Bit Error Rate (BER) and Packet Error Rate (PER) are both metrics used to assess the quality of data transmission, but they differ in their scope. BER measures the rate of errors at the bit level, while PER focuses on errors at the packet level, where a packet is a collection of bits. Essentially, PER is often derived from BER, but it considers the cumulative effect of bit errors within a packet.
Latency and Jitter
Latency and jitter should also be considered, particularly for time-sensitive applications such as SCADA, voice over IP or video streaming. These metrics reflect the time delay and variability in packet delivery, with excessive values potentially indicating sub-optimal antenna alignment or environmental obstructions. The time delay equates to phase errors which means that higher order modulation such as QAM cannot be reconciled correctly.
So, jitter is the timing variation of a signal, while phase noise measures phase changes in the frequency domain. Understanding jitter and phase noise is important, as it affects signal quality in applications like RF systems and precision timing devices.
Polarization
Ensuring polarization alignment is another essential step. Both ends of the link must have matching polarization, either vertical or horizontal, as mismatched polarization can cause significant signal loss. The mismatch loss can easily hit 40 dB of signal loss.
The antenna skew angle is a measurement that indicates how much an antenna must be aligned around its vertical or horizontal axis to align with the link’s optimum signal. A precise skew is required when setting up a new fixed antenna link. In contrast, in cellular systems, the mobile antennas require dynamic calculations and adjustments to maintain the integrity of the link between the smartphone and the tower.
Calculating the correct skew angle often involves considering the antennas position at both ends of the fixed link, the end point’s location, and the Earth’s curvature. Understanding the correct angle ensures the antenna’s polarization matches the other antenna’s polarization, avoiding cross-polarization interference.
Physical Alignment
Physical alignment of the antenna in terms of azimuth (horizontal angle) and elevation (vertical angle) is critical, especially for systems operating at higher frequencies with narrow beamwidths. Even minor deviations can drastically reduce signal quality. Tools such as inclinometers, GPS, or laser sights are often used to achieve precise positioning. In practice, alignment should begin at one end of the link, where coarse adjustments are made while monitoring RSSI and SNR in real time using manufacturer-provided software. Once a strong signal is established, the process is repeated at the other end, with incremental adjustments made to fine-tune the connection.
Conclusion
Ultimately, effective antenna peaking requires a holistic understanding of RF performance metrics and environmental factors. By carefully measuring RSSI, SNR, modulation rate, error rates, latency, phase, jitter, and polarization alignment, and by using appropriate tools for physical positioning, technicians can establish and maintain high-performance, reliable point-to-point wireless links.
About the Author:
Michael Martin is the Vice President of Technology with Metercor Inc., a Smart Meter, IoT, and Smart City systems integrator based in Canada. He has more than 40 years of experience in systems design for applications that use broadband networks, optical fibre, wireless, and digital communications technologies. He is a business and technology consultant. He was a senior executive consultant for 15 years with IBM, where he worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin served on the Board of Directors for TeraGo Inc (TGO: TSX) and on the Board of Directors for Avante Logixx Inc. (XX: TSX.V). He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology. He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now Ontario Tech University] and on the Board of Advisers of five different Colleges in Ontario – Centennial College, Humber College, George Brown College, Durham College, Ryerson Polytechnic University [now Toronto Metropolitan University]. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and seven certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has completed over 50 next generation MOOC (Massive Open Online Courses) continuous education in a wide variety of topics, including: Economics, Python Programming, Internet of Things, Cloud, Artificial Intelligence and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, Indigenous Canada awareness, and more.