Guidelines for Investing in Monitoring and DF Systems

Best Practice Guideline for Investing in Monitoring and Direction Finding (DF) Systems


This Guideline outlines the concepts and methodologies employed in various spectrum monitoring systems and provides guidelines on the expected cost of small to high-end fully integrated systems for monitoring and direction finding.


Without a monitoring and measurement system to record radio frequency activity the spectrum manager cannot evaluate spectrum usage and make appropriate allocation and assignment decisions. Similarly, the spectrum manager can purchase different types of systems for monitoring and DF, from the simple to the very expensive.

The spectrum manager needs to determine and evaluate potential problem areas, determine which equipment is required to address problem and of budget sufficient funds to purchase hardware. Spectrum management operation should operate within the cost recovery revenues generated through spectrum licensing and enforcement. In countries where income from telecom licensing is minimal, the challenges of implementing monitoring systems are even more challenging.

In general, monitoring and DF programs are used to understand occupancy, technical compliance with signal standards, and determine the direction of offending signals and the location of illegal users and assist in resolving interference issues.


There are many economic factors to be considered when developing a spectrum monitoring and DF program and these factors will vary from country to country with each offering a unique set of spectrum monitoring and DF requirements: These include:

  • types of signals - broadcast, cellular, mobile, fixed;
  • seasonal tourism;
  • natural resource or industrial settings;
  • small population (rural), large population (urban);
  • mountainous or coastal terrain;
  • proximity to air and maritime traffic.

The spectrum manager has a number of options which must be assessed to determine the path or approach to the monitoring system. Some of the considerations are:

  1. density of RF traffic;
  2. urban/ village environment;
  3. 24/7 monitoring vs. occasional or ad hoc;
  4. Fixed /mobile sites;
  5. Distance between sites and proximity of sites to targets;
  6. Fully automated - remote or manual operation.

Spectrum managers must assess where the investment money will offer the most benefit. Not all bands are busy or congested in the same way and not all bands are utilized to provide important services to the public.

An area primary concern to spectrum managers is the use of public safety and security bands. Protection of emergency services (police/fire etc), aeronautical, etc. is a fundamental concern of spectrum managers. The VHF/UHF (100 to 500MHz land mobile range normally) are often the most congested bands. The public generally does have access to reasonably inexpensive off-the-shelf radio equipment competing with these essential services creating interference. Monitor and compliance enforcement of these bands should be done, as a minimum. Another area is Land Mobile VHF/UHF where signals tend to radiate in all directions, and due to physical size of the radio apparatus can be difficult to see.

Another important area is to balance spectrum usage where the spectrum manager needs to monitor occupancy/usage to understand spectrum loading. This will assist the spectrum manager when making frequency allocations. Again, the spectrum manager can make pragmatic decisions considering the types of problems and users of spectrum within a particular band. For example, the general public does not have access to cellular or microwave transmitter equipment technology, so it would be reasonable to assume that interference issues arise amongst the competing service providers. Since the service providers are usually interested in providing quality services to their subscribers, they will generally work out issues amongst themselves. Licensed microwave links generally rely on towers which are easily observable, and are point to point with minimal radiation in the local spectrum. For operator’s choosing to operate services in the unlicensed ISM band, interference free services cannot guarantee by the spectrum regulator.

Types of Monitoring Systems

Portable and Transportable Systems

Monitoring systems come in a wide variety of sizes and configurations. A minimum system would be configured to collect only occupancy data. Such a system would consist of a lap top computer and an off-the-shelf commercial receiver and deliver required data and results in a low usage environment. It has the benefit of being completely portable and requires very little room. It is generally manually controlled, with a data download ever couple of days.

A transportable system will generally incorporate a laptop computer, perhaps a receiver and direction finding unit fitting into a ruggedized case used to provide a level of shock and vibration protection

Mobile Systems

A mobile systems can be either a small truck or van which incorporates equipment racks to carry a variety of monitoring receivers, direction finders, spectrum analyzer etc. Mobile monitoring and DF systems often have the capability to remotely connect to a main control site through a wireless link. Depending on the speed of the link, capabilities vary from data file upload/download to complete remote control of its assets. When performing direction finding tasks, it is considered desired able to have the vehicle in motion to reduce multipath effects.

Mobile systems can range in price for minimally functional DF Chase Vehicles used for DF'ing in the 20Khz to 1000 MHz range to much for complex vehicles which can perform as fully functional temporary fixed sites.

Fixed sites

The largest, often more sophisticated and expensive sites when used as National Control Centres are fixed sites. Generally fixed sites have a full compliment of equipment from receivers for occupancy measurements, receivers for technical measurements, direction finding equipment etc.

To get the most from these systems, they are designed to multitask which allows multiple users to access the monitoring equipment. Communication between sites is typically via a high speed network connection, i.e. cable or wireless.

An important issue to consider is system flexibility. Some equipment can be very expensive to procure. A flexible system will allow this high end resource to be shared amongst other fixed/mobile sites. This also has an additional benefit, as new equipment comes available to address new technology it can be easily adapted to the users platform through a simple driver interface. This protects your original investment from becoming obsolete.

Fixed sites should not be installed in the vicinity of commercial transmitter towers where the high levels of emissions will create problems or potentially damage to sensitive receivers. In most cases “high ground” should be staked out by the telecom service providers, creating a greater challenge to locate a monitoring site.

Sub Systems

When considering the deployment of a fixed site proper consideration must be given to the infra structure requirements for such systems. There can be a significant additional up front cost. Some of the areas to review when considering deployment are:

  1. Is there an existing building which can be used/ require a new building?
  2. Existing tower for antennas/ require a new tower?
  3. Vehicle access, is there a road available?
  4. Is electricity available / do electricity lines need to be run (new facility?)
  5. Security, is the building and equipment room secure 24/7?
  6. Environmental protections i.e. heat/air conditioning to protect the equipment?
  7. Desks/place of work for the technicians?
  8. Phone and fax lines.
  9. High speed communication by fixed line or wireless?

Spectrum Monitoring

Purchasing a Monitoring System

When the decision has been made to move forward with the acquisition of a monitoring system, a careful evaluation of the needs and requirements should be undertaken, with a view to monies available in the budget. There are two paths to proceed down. The first is to do a one time purchase for al equipment and subsystems. The second is to take a building block approach, by purchasing in small lots and building up to a complete system. In this scenario, the first step would be to purchase of the necessary equipment to allow the manager to go to the field and perform extensive monitoring, to evaluate spectrum occupancy. Some of the considerations and questions to be answered in planning include:

  • What spectrum is to be covered/monitoring only/direction finding/technical measurement;
  • Fixed/transportable /mobile;
  • How many systems/receivers;
  • Manual/remote control;
  • Use existing buildings/build new buildings;
  • Cable length restrictions i.e. cable losses;
  • Infrastructure requirements i.e. road access, security, power, high speed data links, etc.
  • Personnel requirements/ training.

In selecting monitoring platforms there are a variety of choices out there. From the inexpensive, to the very expensive. Generally the faster the system and more feature rich, the more it will cost. In selecting direction finding equipment (DF), there is a much more limited selection due to the very specialized nature of this equipment, and the limited number of OEM’s.

Table A gives an indication of system costs for basic monitoring tasks.


All Figures in USD

System Type Low End Medium End High End

Monitoring System


Note 1

$50 K

Note 2


Note 3

DF-Fixed Site



100MHz to1.3GHz

$180 K

20KKhz to 3GHz


20Khz to 6 GHz

Antenna $10K $70K $150K





Note 1 : Basic system utilizing a low cost off-the-shelf receiver, with a laptop and software Interface which allows basic occupancy measurement functions scanning at 8-10 channels per second. DF package is lightweight multiple antenna package covering frequencies up to 1300MHz.

Note 2 : Medium priced system incorporating a receiver designed for monitoring with some technical measurement capability scanning at 50 plus channels per second. DF package utilizes a fixed site DF antenna with a combined receiver/DF processor, and a spec sheet of 3 degrees RMS.

Note 3: High end system incorporating a monitoring specific receiver for occupancy measurement with technical measurements to ITU recommendations. Laptop and software for automation of the data collection.

In Table B some of the preceding information is compiled into a representative system incorporating automated control over stand-alone monitoring receiver(s) and DF processor(s). In this configuration two tasks can be conducted simultaneously, i.e. scanning and DF. “F” signifies a fixed site, “T” signifies a transportable and “M” signifies a mobile unit.















-Single LOB DF

- Occupancy/Monitor

- Some Tech. Measurement

- DF Triangulation

- Occupancy/Monitor

- Tech Measurement

Netted DF


- Low End

- High End










$500-900K %20

Sample steps for implementing monitoring surveillance

Phase 1 - Monitor
  • Data collection, finding out what really is happening in your radio spectrum. Concentrate initially on the most populated spectrum, probably land mobile.
Phase 2 - Sort Data legal/illegal user
  • Using the data collected in Phase 2, the manager now has a baseline, and is now in a position to verify legal users/illegal users. The use of appropriate software or database tools can make this step easier.
Phase 3 - Search and Remove
  • With the DF resources available, search out the illegal users. In act corrective action by licensing the user or stopping the use of the transmitter.
Phase 4 - Technical Measurements
  • Final step in the process. To address reported or suspected interference issues, perform the necessary technical measurement to assess the quality of the radio transmitters, and take corrective action as required.


ITU (2002), Geneva. Spectrum Monitoring Handbook.

Fundamentals of Spectrum Analysis, Rohde & Schwarz, 2008

Spectrum Analysis Basics, Agilent Technologies, 4 January 2005

Spectrum Monitoring Approach prepared for the Telecommunications Authority Suriname by McLean Foster & Co. February 2005, Almonte ON

Learn More