Lines on a map are the most usual means of depicting the coverage area of an FM station. Most often, stations use maps showing the 1 millivolt, the 0.5 millivolt or sometimes even lower contour values to define their coverage areas for clients, agencies and listeners.
Often these map contours are derived from the ERP (effective radiated power) and HAAT (height above average terrain) on each of eight or more radials. In other cases, the map contours may be derived from empirical data or listening tests. In rare cases, they may even be drawn from data collected by aircraft measurements of the antenna pattern.
The trouble with map contours is that they don’t really tell the whole story. Radio veterans know that there is usually a good bit of coverage beyond the mapped contour line, and that there are usually significant holes in the coverage within the mapped coverage area.
In short, it is difficult, if not impossible, to depict the overall quality of an FM station’s signal with a contour line on a map. There are simply too many variables.
To address this problem, Audemat has developed a product called the FM_MC3.2 Precision Monitor. It allows the user to evaluate the overall quality of an FM station’s signal quite effectively. It consists of several software modules.
The first module is used in the process of making signal measurements. It is used with a special calibrated FM receiver and a GPS receiver in a measurement campaign wherein the signal of the station or stations being evaluated is measured while driving.
The user selects the route/locations, and a laptop computer records mobile, dynamic field-strength data on each of up to 99 stations along with GPS latitude/longitude data for each measurement point.
A special calibrated whip antenna mounted on the vehicle roof is connected to the FM_MC3.2, which feeds field-strength data along with a number of other parameters for each station to the laptop. The computer records the data for later use.
The more stations that are being measured, the longer the scan time and thus the longer time between individual measurements on each station (three measurements per second). Multiple-station monitoring provides an excellent means of comparing the performance of different stations serving a particular area.
In addition to field-strength data, the FM_MC3.2 provides audio analysis of a single station in its MCAF02 software. In this function, a much more in-depth study of a particular station’s performance can be made.
A station’s performance at a particular location depends on many more factors than simply field strength. The audio analysis looks at and records composite and pilot levels, subcarrier levels, left and right audio, L+R and L-R as well as multipath.
Precision modulation analysis is another function of the MCAF02 software. This mode provides analysis of modulation mask, peaks, density and cumulative modulation. The program can record peak and signal data for up to 72 hours in a particular location, allowing tracking of station performance over varying environmental and operating conditions.
A precision RBDS analyzer is included that looks at the RBDS subcarrier, if used. The analyzer also records bit errors as a measurement of overall RBDS subcarrier performance.
The software utilizes all the functions of the FM-MC3.2 to record the above parameters for one station. As the operator drives the route to be evaluated, the FM-MC3.2 sends a data stream every 20mS containing field strength, composite level, pilot, RBDS, left audio, right audio, L+R and L-R to the notebook computer, which records the data along with GPS-derived location data for each point and the audio.
From these eight parameters, the software calculates several other parameters: RF average, multipath, subcarrier stability and multiplex (composite) peaks. It then analyzes these parameters together in an algorithm that determines an overall “Quality Index” for the signal at each point.
An Audemat spokesman told us, “Daniel Werbrouk, president of Audemat, has been concerned for many, many years on how to measure FM quality. Before Goldenear there were only two ways to determine if an FM signal is a ‘good’ signal.
“One way is the human ear, but since the ear is totally subjective, the results are not accurate. The ‘Quality Index’ is the result of several years of working with various regulation authorities and broadcasters all over Europe, so it was not created in a vacuum of one person’s concept of a good signal.”
Because the automobile is a primary listening environment, mobile Goldenear signal measurements and quality evaluations probably are the most accurate means of determining the overall performance of an FM station. The operator has complete control of the route to be measured and can thus provide information on specific areas of interest.
For example, a wide, overall coverage area or a specific target area can be the focus of the measurements, providing valuable information to the station management, engineering and sales teams.
Once the route has been driven and the measurement data collected, another software module, the Goldenear Expert, is used to massage the data and configure it before it is viewed by the end user.
The polished data are then provided to the end user using the Goldenear, which provides a geographical representation, a curve representation along with raw and calculated data, a text representation along with all acquired data, and a cartographic representation showing identifiable map features.
Each of the various views is selectable with a mouse click, and the recorded audio at each location is available with software start, stop and volume controls. The bottom of the screen constantly displays signal level and display zoom extent.
The current point can be moved to any location in the measurement campaign by simply clicking on the point on the route displayed on the screen, or by using a sliding control bar software control.
The campaign display shows the route along with a color representation of any of the available quality marks at every location along the route. This makes it easy to see signal problems in particular areas at a glance. The user can then zoom in on areas of interest and even listen to the recorded audio in those areas to add another dimension to his understanding of the signal quality at that point.
Goldenear, with all its capabilities, isn’t cheap. It carries a price tag of $23,495 including the software and the FM_MC3.2 receiver. It does not include the laptop computer for the measurements.
This may seem steep, but when you consider the cost of a standard FM field-intensity meter that provides only field-strength data, the price becomes much more reasonable. The product can pay for itself by allowing station management to focus its marketing efforts on areas where reception quality is demonstrably good. Clients can be shown campaign data in whole or in part to demonstrate the quality of the signal.
For more information, call (866) AUDEMAT, visit the Audemat Web site at www.audemat.com or send e-mail to [email protected]