Part 9C: The Truth About Scanners and Cellular

Members of the public and new hobbyists often ask if "police scanners" can really hear cellular phones and if so, if it is legal.  For most hobbyists, legal and ethical issues are now a moot point as virtually all modern cellular phones operate in digital formats that cannot be heard on any scanners.  However, until recently, that was not the case.  The voice transmissions from cellular phones were in narrow FM, the same mode used by virtually all land-mobile communications, from police to taxicabs.  The introduction of cellular service in the early 1980's, the arrival of 800 MHz scanners shortly thereafter, and the alleged nature of early cellular calls made for an interesting collision of competing interests.  On paper, the cellular phone companies won, with sweeping legislation that for the first time punished individuals for merely listening to certain radio signals.  In reality, anecdotal evidence indicates nothing could or did stop these signals from being overheard until cell phones went digital.   

The early years...

The cellular phone system was not the first time telephone calls had been patched over radio.  Over 60 frequencies had already been allocated for this purpose in the widely monitored VHF and UHF bands.  The frequencies were anything but secret and conversations were apparently monitored even in the days of crystal scanners.  The limited number of channels meant that radiotelephones were available only to a few well-financed customers.  Radiotelephone users had little expectation of privacy; Nor did federal law provide any illusion of privacy.

In the early 1980's, telephone companies and independent cellular carriers began offering service on the new cellular networks, starting with large cities.  The new cellular system featured 832 channels, over 10 times the previous capacity, and an innovative network of coverage "cells" provided by numerous towers.  The arrangement of such "cells" was placed to ensure continuous coverage as caller traveled throughout the range of the system. 

Also unlike previous systems, channels were located in the new 800 MHz band, made mostly from former UHF TV channels 70 through 83.  As equipment for the band was difficult to make and no stations yet used it, few scanners covered the band in the early 1980's.  Cellular companies promoted the apparent privacy of the new system, despite its reliance on standard FM technology for the audio.

By late 1985, scanners that could tune the 800 MHz band hit the consumer market as several police departments were migrating to these frequencies.  Published articles claimed that the expensive cell-phone service was frequented by drug dealers and organized crime.  Whether true or not, such reports further increased interest in hearing cell phones.  Realizing their customer base would not like being monitored, cellular companies needed to act quickly.  Rather than using scramblers or digital encryption, like sensitive government agencies, they sought a legal solution.  In 1986, Congress approved the Electronic Communications Privacy Act (ECPA), which for the first time, made it illegal to listen to certain radio signals, most notably cellular phone calls and voice pagers. 

The controversy Continues

Despite the new law, cellular phone calls only became less private.  As more police departments also began using 800 MHz frequencies right next to the cell-phone band, more 800 MHz scanners were sold.  Many scanner manufacturers attempted to block out cellular calls while allowing reception of adjacent police, fire and other 2-way communications.  Such radios proved easily susceptible to monitoring, usually by clipping or adding a diode to a circuit board.  Even without modification, most radios would receive many cellular calls due to various quirks in the way radio receivers work. 

Most cellular monitoring occurred in secret and caused few controversies as few people knew about it.  From time to time, a listener would overhear a celebrity or politician and unwisely tape the conversation and give it to news media.  In the early 90's, Douglas Wilder, then Virginia governor, was overheard badmouthing a rival.  The British royal family also had their share of embarrassment.  In response, the cellular industry sought to ban the manufacture or importation of scanners capable of receiving or being easily modified to receive cellular frequencies.  In 1992, they succeeded by tacking the measure on to the unrelated Telephone Disclosure and Dispute Resolution Act.  The ban applied to new models applying for FCC certification starting in April 1993, and older models still in production starting in April 1994. 

Despite the new law, a plentiful supply of older scanners remained available on the used market, often selling well above comparable models made after the ban.  Even newer scanners could receive cellular calls due to a quirk in the properties of radio signals.  Through a method called "image reception", the calls could be heard by tuning the radio to nearby frequencies approximately 21 MHz away.  Interestingly enough, this method worked only on the lower-cost double conversion scanners.  It existed long before the cellular controversy developed.  "Images" that appeared on the wrong frequencies were usually considered a nuisance; these signals often confused new hobbyists and even prevented the reception of desired signals, such as police or aircraft.  With the case of cellular, though, at least some hobbyists welcomed this "interference." 

Worse yet, cellular signals often appeared on totally unrelated frequencies due to "intermodulation", a condition caused by strong signals mixing together in overloaded receivers.  Indeed, scanner receivers reviewed in magazines in the late 90's often complained of unwanted cellular phone interference in the aircraft or police bands!  Apparently it was difficult to design a receiver that was sensitive to the weaker police, fire, and aircraft signals while also filtering out much stronger cellular signals on nearby frequencies. 

In 1997, the issue of cellular monitoring again reached the mainstream media.  A congressional associate of Newt Gingrich was overheard talking to the then-Speaker of the House about an ethics scandal.  During the media furor that followed, a bill was introduced that would have virtually outlawed scanners.  A outcry from the hobby community resulted, and most of the bill was shelved. 

Scanner manufacturers agreed to stop making the low-cost double-conversion scanner models that were susceptible to image reception on nearby frequencies.  On other models, the circuit boards were coated in epoxy to prevent modifications to allow cellular reception.  Cellular conversations remained easy to overhear, however, and any congressional action likely would have accomplished little due to the number of existing scanners.  If anything, the attention brought to the issue likely encouraged many who had no other interest in the radio hobby to listen to calls.   

Technological Change Ends an Era

In the early 2000's, technological change caused what no legislation could.  The number of cell phones and the duration of calls had increased rapidly throughout the 90's as the cost of service decreased.  Cellular systems soon were running short on available channels and also wanted to add new features like text-messaging, email, and internet access.  The solution was to switch from analog FM to digital modes, which, coincidentally, could not be monitored on scanners.  By 2004, approximately 80% of all cellular calls were digital.  Virtually all calls are now digital except in a few rural areas.  Cellular providers will no longer be required to even support analog cellular service in 2008. 

There is no equipment available to consumers that can receive digital cellular signals.  Federal law prohibits such decoders; even if the event such equipment was technically feasible, it could not be marketed to consumers. 

For detailed information on specific scanner models, please refer to Category 6: Radio Scanners Listed By Category. 

Part 9B: History

Part 9D: About the Author