Everything Works Except Voice Will Not Transmit

Oftentimes, a radio scanner user will notice that their scanner does not accept all frequencies and that the scanner will automatically move to a frequency other than the one it is tuned to. It is important to understand that this is normal and does not indicate a problem with the scanner.

All scanners work using a series of crystals or electronic oscillators. These determine the frequencies that the scanner works with. Individual frequencies are created by combining the frequencies of the oscillators. This is done to allow the maximum number of frequencies possible; however, there is a "step rate" that determines the smallest incremental change between one frequency and the next. If the frequency being input is between two frequency steps, the scanner will round it off to the closest step. This still allows for reception of the signal, as all radio signals have some "spillover."

The step rate issue does not need to be fixed, as the scanner will work fine regardless. In fact, it cannot be fixed, as the scanner is working properly.

When a scanner stays on any particular frequency, it indicates that the scanner is receiving a signal on that frequency. If there is no sound coming out of the speaker, it could be an unmodulated signal (a signal without any voice information). A number of things can cause this; it is not necessarily an indication that the radio is transmitting without any modulation.

To troubleshoot the problem of a scanner staying on a particular frequency, first remove or disconnect the antenna, checking to see if the problem persists. If it goes away, this verifies that the scanner is picking up a signal, even though it is unmodulated. If the problem continues, either the signal is so strong that the scanner does not need an antenna, or the problem is with the scanner itself.

Trying the scanner in an alternate location can eliminate the possibility of a very strong signal. If the problem disappears in a different location, it was a strong signal. If it persists, there may be a problem with the scanner.

There are two ways of dealing with the problem of a strong signal. The first is to program a lockout for that frequency if the scanner has that option built in. This will allow the scanner to skip over that frequency as it searches. The second is to replace the external antenna with an attenuated antenna. This would either be a partially shielded antenna or an external attenuator installed inline between the antenna and the scanner. However, this option cuts down all radio signals received, not just the problem frequency.

For scanners that are mounted in vehicles, there is an additional possible cause for this problem. The vehicle's engine, and specifically, the spark plugs, can emit RF (radio frequency) interference. This is also a common problem for CB (citizen's band) radio users. At times, the same problem will manifest as static noise instead of as a quiet frequency.

An inline filter on the DC power line for the scanner is the first thing to try. If the interference is coming through the power line, this might solve the problem. If the problem is not solved, the second thing to try is grounding the vehicle's exhaust pipe. The exhaust pipe is normally fully insulated (electrically) from the vehicle, so grounding it causes it to function like a giant electrical capacitor. A ground wire can be attached to the exhaust pipe with a standard hose clamp. Be sure to clean off the surface before attaching. The other end of the wire can be connected to any bolt or screw on the vehicle's chassis.

The other possible direction for solving this problem is moving the scanner's antenna. The farther it is from the source of the RF (the engine), the less likely it will be to pick up that interference.

Any scanner has a number of crystals or oscillators in it that control the frequencies which the scanner picks up signals on. In the process, it creates what are known as "birdie signals." These are false signals, created by the scanner, which are a multiple of the output frequency of one of the oscillators. The birdie signal is most often created from the sum or difference of the frequencies of two or more oscillators.

Most of these birdie signals occur outside of the range of the scanner. However, it is possible to have birdie signals that are within the scanner's range. In this case, the signal will sound like static or another spurious noise. The solution is to program a skip into the scanner for the frequency of the birdie signal.

The most common frequencies for birdie signals are as follows: 31.05 MHz, 41.40 MHz, 51.75 MHz, 113.85 MHz, 124.20 MHz, 134.55 MHz, 144.90 MHz, and 155.25 MHz.

Sometimes, a scanner may pick up transmissions on a wrong frequency. This is due to something called harmonics. As the radio signal goes out, it also sends out harmonic signals. These signals are half the length or another fraction of the original signal wavelength. Signals that are being picked up on the wrong frequencies are the harmonics of the original signal.

These harmonics are weaker signals than the original. To eliminate them, one needs to add an attenuator inline between the antenna and the scanner.

Sometimes, only very low-volume audio will come through the headphone jack. This is because the headphone jack on a scanner, or on any electronic device, has a very low-powered amplifier connected to it. It is intended to power only the small speakers found in headphones, which are positioned extremely close to the listener's ear. To use an external speaker on a scanner that does not have an external speaker connection, one would need to use an amplifier or an amplified speaker.

Computer speakers are amplified speakers. The speaker connection for the computer uses the same amplifier as the headphone jack. The internal amplifier in whichever of the speakers connects directly to the computer amplifies this audio signal, and then sends one channel to the other speaker.

Using computer speakers for scanners can solve a problem with low volume. When using computer speakers in a vehicle, it is necessary to use speakers that are USB powered. A USB power adapter for the vehicle ' s cigarette lighter can then be used to power the speaker.

Battery - powered ( handheld ) scanners can have problems that do not exist for base -station or vehicle - mounted units. These problems are specific to the batteries.

If fully charged batteries are installed in the scanner and it will work for more than a few seconds or minutes, it indicates that there is not a good contact somewhere in the battery box. Most likely, there is a small amount of corrosion on one of the battery contacts. This is a common problem with all battery-operated devices, from flashlights to portable computers.

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