Two Sets of Calling Frequencies, Two Different Jobs — Annotated Notes & Key Takeaways

If you look at the ARRL band plans for 2 meters and 70 centimeters, you will notice two different kinds of calling frequencies listed. One set is labeled “calling frequency.” The other is labeled “simplex calling frequency.” They sit on different frequencies, and they are meant for different modes. At first glance, the distinction can seem arbitrary. Why have two calling frequencies on the same band? The material here explains that the difference comes down to modulation, operating style, and the way the band plan tries to keep order on the air. The calling frequencies are not interchangeable. Each one has a job.
 

The short answer is that 144.200 MHz on 2 meters and 432.100 MHz on 70 centimeters are intended for SSB. The simplex calling frequencies, 146.520 MHz on 2 meters and 446.000 MHz on 70 centimeters, are intended for FM. That is the core of it. But the reasoning behind that split, and the practical rules that come with it, are worth unpacking.
 

What the Calling Frequencies Are For

 

On 2 meters, 144.200 MHz is the national calling frequency. On 70 centimeters, 432.100 MHz plays the same role. These frequencies are associated with SSB, which stands for single sideband. SSB is a voice mode, but it is not the same kind of voice mode as FM. It is more efficient in terms of bandwidth, and it is often used for weak-signal work, long-distance contacts, and contacts that do not rely on repeaters. In the band plan, these frequencies are the place to start if you are looking for an SSB contact.
 

The material notes that SSB, CW, and other narrowband or weak-signal modes are generally used for longer-distance, simplex-only communication. That phrase “simplex-only” matters. It means the communication happens directly between two stations on the same frequency, without a repeater. There is no infrastructure in the middle. One station transmits, the other listens, and then they switch. That is the basic rhythm of a simplex contact.
 

The calling frequency itself is not meant for long conversations. It is a meeting place. You call CQ there, you find someone, and then you move to another frequency to continue the contact. That keeps the calling frequency open for the next person who wants to make a contact. This is a convention, not a hard law in most cases, but it is part of good operating practice. The band plan expects it.
 

Simplex Calling Frequencies and FM

 

The simplex calling frequencies are 146.520 MHz on 2 meters and 446.000 MHz on 70 centimeters. These are intended for FM. FM is the mode most commonly used on VHF and UHF for local communication. It is clear, easy to tune, and works well with repeaters. But it also works in simplex mode, which is why these frequencies exist.
 

The material points out that the word “simplex” in general amateur use often implies FM. That is because FM is the mode most people think of when they think of simplex on 2 meters and 70 centimeters. SSB, CW, and other modes are usually described differently. They are not usually called “simplex” in casual conversation, even though they are often used in a simplex way. So when the band plan says “simplex calling frequency,” it is signaling that this is the FM calling channel.
 

There is a practical reason for separating the two. If you put an SSB signal on an FM calling frequency, or an FM signal on an SSB calling frequency, you are likely to confuse people and interfere with the intended use. The modes do not hear each other well. An FM receiver may not demodulate SSB properly, and an SSB receiver may not handle FM. Keeping the calling frequencies separate keeps the band organized.
 

The material also explains a rule that applies to these frequencies: no repeaters should transmit or receive on calling frequencies. Cross-band communication and remote control are also not supposed to use them. The calling frequency is for making contact, not for hosting a permanent repeater or a remote link. If you want to talk for more than a few minutes, you should agree with the other station to move to a different frequency. That keeps the calling frequency free for others.
 

The Definition Problem: What “Simplex” Really Means

 

One part of the material that I found harder to follow is the discussion of what “simplex” actually means. In everyday amateur radio talk, simplex means transmitting and receiving on the same frequency, without a repeater. That is the common usage. But the material includes a correction that points out a technical distinction.
 

In data communications, “simplex” means one-way communication only. A device transmits, and it cannot receive. That is different from what hams usually mean. In amateur radio, what we call simplex is actually half duplex. Half duplex means one station transmits at a time, but both stations can take turns transmitting and receiving. Full duplex means both stations can transmit and receive at the same time. The material says that amateur radio simplex is really half duplex communication.
 

This is a terminology issue, not a practical one.

If you say “simplex” on the air, everyone knows what you mean. You mean no repeater, same frequency, take turns. But if you are writing a paper or explaining the concept to someone from outside the hobby, it helps to know that the technical definition is different. The material does not resolve the terminology debate. It just notes the discrepancy and leaves it there. I think that is fair. The important thing is to understand what the band plan means when it uses the word.
 

Line A and Regional Differences on 70 Centimeters

 

The material also includes a note about a complication on the 70-centimeter band. In some parts of the United States, above a certain line called Line A, simplex calling on 446.000 MHz is off-limits. Line A is a coordination boundary that affects which frequencies can be used in certain regions. The calling frequency at 432.100 MHz is still available, but the simplex calling frequency is not.
 

This means that in those areas, operators may use 432.100 MHz for FM calling instead. The material mentions that a local group in Ohio used 432.1 MHz for FM calling because of Line A. That is a regional adaptation. It shows that band plans are not always uniform across a large country. Local conditions, coordination agreements, and geography can change how the plan is applied.
 

I found this part of the material a bit thin. It mentions Line A but does not explain exactly where it is or how it affects operators in different states. A reader who is not familiar with Line A would need to look it up separately. The material assumes some background knowledge. That is a limitation, but it is also a reminder that band plans are complex documents that interact with regulations and regional coordination.
 

The 446.000 vs. 446.200 Confusion

 

There is also a small but important detail about the 70-centimeter simplex calling frequency. The correct frequency is 446.000 MHz, not 446.200 MHz. The material includes a correction because one entry had the wrong number. This kind of error is easy to make, and it is easy to fix. But it matters because if you program the wrong frequency into your radio, you will not find anyone. The correct frequency is 446.000 MHz. The 2-meter simplex calling frequency is 146.520 MHz, not 146.250 MHz. The material corrects that one too.
 

These are minor points, but they are the kind of details that trip up new operators. A band plan is only useful if you read it accurately. The corrections in the material are a good reminder to double-check frequencies before you rely on them.
 

What the Material Leaves Unsettled

 

The biggest unanswered question in the material is how strictly the calling frequency conventions are followed in practice. The band plan says you should move off the calling frequency after making contact. But not everyone does. Some operators stay on the calling frequency for long conversations, especially on FM. That can make it harder for others to use the frequency for its intended purpose. The material does not offer a solution to this. It just states the convention.
 

Another open question is how the SSB calling frequencies are actually used. On 2 meters, 144.200 MHz is the SSB calling frequency, but SSB activity on 2 meters is not as common as FM activity. In some regions, you may call CQ on 144.200 and hear nothing. In others, there may be regular activity. The material does not provide a map of activity. It assumes that the reader understands that calling frequencies are a starting point, not a guarantee.
 

The Line A issue also remains partially unresolved. The material mentions that simplex calling is off-limits above Line A, but it does not explain what operators should do instead in those areas. It gives one example from Ohio, but it does not generalize. A reader who wants to operate on 70 centimeters in a Line A region would need to consult local coordination documents or ask experienced operators.
 

Finally, the terminology debate about simplex versus half duplex is interesting but not fully resolved. The material notes the discrepancy between amateur usage and data communications usage. It does not say which one is “correct.” In practice, both are correct in their own contexts. The confusion only arises when someone from one background talks to someone from another. The material does not try to settle the debate. It just points it out.
 

What This Means for a New Operator

 

If you are new to 2 meters and 70 centimeters, the practical takeaway is simple. Learn the four frequencies. On 2 meters, 144.200 MHz is for SSB, and 146.520 MHz is for FM simplex. On 70 centimeters, 432.100 MHz is for SSB, and 446.000 MHz is for FM simplex. If you are operating FM, use the simplex calling frequencies. If you are operating SSB or CW, use the calling frequencies. Do not use a repeater on a calling frequency. Make your contact, then move to another frequency to continue the conversation.
 

It also helps to know that “simplex” in amateur radio means same-frequency, no-repeater communication. It does not mean one-way communication, even though that is what the word means in other contexts. When you hear someone say “simplex,” they mean half duplex. That is the common usage, and it is the one the band plan uses.
 

The material is not a comprehensive guide to band planning. It is a focused explanation of one distinction. But it is a useful distinction, and it is one that every VHF/UHF operator should understand. The calling frequencies are not all the same. They serve different modes, different purposes, and different operating styles. Knowing which is which helps you use the band correctly and helps keep the airwaves organized for everyone else. That is the real value of understanding the difference.