One of the most common misconceptions of radio reception is that the proximity of a transmission tower correlates directly to the quality of reception. Although it is true that one of the major factors of reception is distance, a number of other factors can, and often does, affect the reception quality. It take a qualified technician with the experience and the RF tools to measure and interpret the many facets of radio signal that can take the mystery out of why or why not certain channels are receivable and others are not.
Type of signal
Different types of radio broadcasts have different reach.
Although much of a transmitter’s ability to broadcast over certain distances depends upon the wattage it is allowed to operate, the type of signal can matter greatly. Analog conventional channels are part and partial of an age gone by, although still widely used. These channels were used when the demand for wireless bandwidth was low; prior to cell phones, Nextel, and all the many other wireless devices available today. These transmitters were designed to broadcast signal many miles, sometimes as far a 50 or 60 miles depending upon elevation and other RF factors.
Although these transmitters were strong, the efficiency of the network was limited. One radio channel would be full occupied during the entire length of a discussion. Although this sounds obvious, newer technology (specifically trunked radio systems) economized on channel use in order to created more bandwidth availability for simultaneous conversations and transmissions.
As the radio spectrum was utilized for cell phone use, Nextel, and the many other parts of the digital spectrum, it became apparent that the ever increasing demand for wireless bandwidth could not be sustained without real changes.
Enter trunked systems. A trunked system is a radio system that is designed to share channels and the bandwidth they occupy among many conversations. To clarify, there is a control channel that assigns a talk group frequency to a conversation while a person is talking. When that person stops talking and realizes his or her finger from the transmitter microphone, the control channel then releases that channel into the pool of channels available for every radio, but keeps the conversation connected by the two radio operators. When the responding radio operator presses his microphone, the control channel then assigns the same or a new talk group frequency to allow the conversation to continue. This continues until there is enough silence that the control channel releases the transmission connection completely.
Trunked system transmitter are only designed to transmit up to 12 miles, but repeated again for another 12 miles. This effectively achieves two goals:
- At the point in which a repeater is 12 miles from the border of a county, the build out of the radio network ends. This prevents the interference of one radio system with another from county to county.
- This allows for the ability over effectively oddly shaped counties that may have bends in their borders or a rectangular shape.
When one tests reception, confusion often occurs when a county, department, town, or other radio system is received but only partially. Many times this is due to reception being received by the older, conventional radio signal but not the newer, digital, trunked systems.
Finally, FCC regulations are in place that limit the wattage and signal strength of modern radio systems. This ties in to the aforementioned wattage and reach of trunk systems. By legally limiting the power of the transmitters used for public safety radio, the FCC ensures that there is far less interference between radio systems and many public safety radio mishaps can be averted.
Type of Radio
Even among the same brand, there a vast differences in radio sensitivity, function, and reception. There is an obvious difference in radio reception capability of a $4,000 2-way radio used by law enforcement and the digital public safety police scanner that can be purchased for all of $400. Yet there is also a significant difference between the sensitivity of the two top selling models of Uniden scanners, the Bearcat BCD996P2 and the Bearcat BCD536HP scanners as well as those produced by Whistler.
The radio equipment one uses to receive the transmissions they want to hear can make all the difference in the world.