The Radio Shack Pro-197 does not receive control channels

The Radio Shack Pro-197 is a handheld scanner that picks up radio transmissions on VHF, UHF, and 800 MHz frequencies. It can monitor police, fire, emergency services, and other public radio traffic. However, it cannot receive control channels — the special frequencies that radio systems use to send commands and data to their radios, rather than voice traffic.

Control channels carry the instructions that tell a radio when to transmit, what frequency to use next, and whether a call is coming in. They are not meant for listening. The Pro-197 lacks the digital decoding hardware needed to read these signals, so even if you tuned to a control channel frequency, you would hear only noise or silence.

Key Takeaways

  • Control channels are the frequencies a radio system uses to send commands to radios, not to carry voice conversations.
  • The Pro-197 can receive voice traffic on conventional frequencies but cannot decode the digital signals that control channels use.
  • Modern digital radio systems like P25 and DMR use control channels; older analog systems do not.
  • If you want to monitor a digital radio system, you need a scanner with digital decoding capability, not the Pro-197.

How control channels work in radio systems

Radio systems have two types of frequencies: voice frequencies and control frequencies. Voice frequencies carry the actual conversation — when a police officer talks to dispatch, that happens on a voice frequency. Control frequencies send the behind-the-scenes instructions that make the system work.

When a dispatcher sends a message, the control channel tells all the radios in the system that a transmission is coming, which frequency to listen on, and who the message is for. Without control channels, every radio would have to monitor every frequency all the time, which would drain batteries and create chaos. Control channels let the system be efficient and organized.

Analog radio systems — the older kind — do not use control channels at all. They use a single frequency or a small set of frequencies, and any radio can transmit on them. Digital systems like P25 (used by many police and fire departments) and DMR (used by some commercial and amateur radio) rely on control channels to manage traffic.

Why the Pro-197 cannot receive control channels

The Pro-197 was designed to receive analog voice transmissions. It has an analog receiver and an analog demodulator — the hardware that turns radio waves into sound. Control channels transmit digital data, not voice. The Pro-197 cannot decode digital signals, so it cannot read what a control channel is sending.

Even if you manually tuned the Pro-197 to a control channel frequency, you would hear static or nothing at all. The radio would not know how to interpret the digital information, and it has no way to display text or data on its screen. It is built to do one job — receive analog voice — and control channels are outside that job.

The difference between voice frequencies and control channels

On a conventional analog system, the voice frequency and the control frequency are the same thing. When someone talks, they are talking on the frequency. There is no separate control signal.

On a digital system, they are separate. The control channel is always active, sending out a stream of data that tells radios what to do. When a call comes in, the control channel tells the receiving radio to switch to a different frequency to hear the actual conversation. This is called trunking. It lets one system handle many more calls than a conventional system can, because voice traffic is spread across multiple frequencies instead of all happening on one.

A scanner that can receive a trunked digital system needs to be able to decode the control channel in real time. It has to read the data, understand which frequency the voice traffic is on, and switch to that frequency fast enough to catch the conversation. The Pro-197 cannot do this.

What the Pro-197 can and cannot monitor

The Pro-197 works well for conventional analog systems — the kind where all the traffic on a given agency happens on one or two fixed frequencies. Police and fire departments in smaller towns often use conventional systems. You can program the Pro-197 with those frequencies and listen to all the traffic.

The Pro-197 cannot monitor trunked digital systems, which most large cities and many counties use. It also cannot monitor P25 Phase 2 systems, which use a more advanced form of digital encoding. If you try to listen to a trunked system with the Pro-197, you will miss most of the calls because the radio cannot follow the control channel instructions that tell it which frequency to tune to next.

The Pro-197 does have a digital mode for P25 Phase 1 systems, but this is limited and does not include control channel decoding. For full monitoring of modern digital systems, you need a scanner like the Uniden SDS100 or Whistler TRX-1, which have the hardware and software to decode control channels and follow trunked traffic.

How to know if a system uses control channels

If you are trying to monitor a specific agency and want to know whether it uses control channels, check the Radio Reference database (radioreference.com). Search for your city or county and look at the frequency listings. If the listing shows a control channel frequency separate from voice frequencies, the system is trunked digital. If it shows only voice frequencies with no control channel listed, it is conventional analog and the Pro-197 can receive it.

You can also call the agency directly and ask what type of radio system they use. Many will tell you whether they are on a conventional or trunked system. If they say P25 or DMR, the system is digital and uses control channels.

Frequently Asked Questions

Can I listen to control channels if I upgrade my scanner?

You cannot listen to control channels themselves — they are data, not voice. But a scanner with control channel decoding can read the data and automatically follow trunked systems to the voice frequencies where the actual conversations happen. That is what you really want to do.

Will the Pro-197 ever be able to receive control channels?

No. The Pro-197 is a fixed hardware design from an older generation of scanners. It cannot be updated with new decoding capability because the physical receiver and processor do not support it. You would need a different scanner.

What does it mean when a scanner says it has P25 capability?

P25 is a digital standard used by many public safety agencies. A scanner with P25 capability can decode P25 voice transmissions. Some P25 scanners can also decode control channels, but not all — check the specs. The Pro-197 has limited P25 support and cannot decode control channels.

If I listen to a control channel frequency on the Pro-197, will I hear anything?

You will hear noise or silence. Control channels transmit digital data that sounds like static or chirps to an analog receiver. You will not hear voice or any intelligible sound because the Pro-197 cannot decode the digital signal.