Section 7.1: FM Operation #

Alright, new hams, let’s dive into the world of FM (Frequency Modulation) - the bread and butter of many Technician class operators. Think of FM as the smooth jazz of radio modes: clear, crisp, and relatively noise-free.

Why FM? #

FM is the go-to mode for most local communications, especially on VHF and UHF bands. Why? Because it handles noise like a champ. While AM (Amplitude Modulation) gets all jittery when there’s electrical interference, FM keeps its cool, delivering clear audio even in urban jungles full of electronic noise.

How FM Works #

Here’s how it works: instead of varying the strength of the signal (like AM does), FM varies the frequency slightly. It’s like changing the pitch of your voice rather than the volume. This nifty trick is why FM sounds so clear on your car radio and why it’s perfect for local ham chats.

As we discussed in Section 3.6, there is also PM (Phase Modulation) which is so similar to FM in practical use that most hams don’t know the difference. For convenience we just refer to it as FM since the main difference has to do with how the transmitter generates the signal.

Types of FM Operation #

Now, let’s talk about using FM in the ham world:

1. Simplex Operation: This is direct radio-to-radio communication. You and your buddy are on the same frequency, taking turns to transmit and receive. It’s great for local chats or emergency communications when repeaters might be down.

   Hey, want to know a handy frequency to remember? 146.520 MHz is the national calling frequency for FM simplex operations on 2 meters. It’s like the radio equivalent of a public square where hams gather to make initial contacts before moving to another frequency for a longer chat – or just somewhere to “hang out” when driving a long distance where you may find people to talk to.

2. Repeater Operation: Remember those range-extending marvels we talked about earlier? Most repeaters use FM. They listen on one frequency and transmit on another, vastly extending your range.

3. Narrow Band FM: Many modern radios use Narrow Band FM to squeeze more channels into our precious spectrum. It’s like the radio equivalent of compact parking - same car, smaller space.

FM Operating Tips #

When operating FM, remember:

• Speak clearly and at a normal pace. No need to shout - the mic is right there!
• Leave a pause between transmissions. This gives others a chance to join in or signal an emergency.
• Use simplex when possible. It keeps repeaters free for those who really need the extra range.
• Tune accurately: FM signals require precise tuning for clear audio. If you tune your FM receiver slightly above or below the signal’s frequency, the result will be audio distortion. Unlike other modes where off-frequency tuning might change the pitch or create a tone, FM tuning errors lead directly to poor audio quality. Make sure your receiver is properly set to the exact frequency to avoid this issue.

FM Quirks #

FM has some quirks you should know about:

• Capture Effect: The strongest signal wins. If two stations transmit simultaneously, you’ll usually hear only the stronger one. If the signals are roughly the same strength then likely neither will be understandable.
• Near-Far Problem: A nearby station can sometimes overpower a more distant repeater on a nearby frequency. If this happens, try adjusting your squelch or using a directional antenna.

Common Radio Codes #

While not specific to FM itself, there are a few special “codes” you should know about; these are left over from back when everyone used morse code but they are used often enough that you’ll want to be familiar with them and what they mean:

• QSY - “I’m changing frequency” or “Change your frequency to…” It’s often used when you want to move a conversation to a different channel.
• QTH - “My location is…” This is used when sharing your geographic location.
• QRM - “I’m experiencing interference from other stations.” If you’re having trouble hearing due to other signals, this is the code to use.
• QRN - “I’m experiencing interference from atmospheric noise or static.” Think thunderstorms or other natural interference.
• QSL - “I confirm receipt of your transmission” or simply “I understand.” It’s like saying “roger that” or “copy.”
• QRZ - “Who is calling me?” Used when you hear someone calling but can’t quite make out their callsign.
• 73 - “Best regards” or “Goodbye.” This is a friendly way to end a QSO (conversation).
• 88 - “Love and kisses.” A more affectionate sign-off, often used between ham radio couples or very close friends.
• CQ - “Calling any station.” This is used when you’re looking for anyone to talk to.
• DX - Distance or foreign countries. “Working DX” means making long-distance contacts.

These codes and shorthand terms are part of the unique language of amateur radio. They’re handy for quick communication and are widely understood by hams around the world. Remember, while these aren’t specific to FM, you’ll hear them used across all modes of operation.

These may not seem important to learn, but they are a big part of the lingo in the amateur radio world – if you don’t know what they mean you may feel left out in some conversations. For those who need a better reason, though, several of them show up on test questions ;-)

Exam Tips #

For the exam, remember that FM is less susceptible to noise and interference compared to AM, but it uses more bandwidth. Also, if you’re hearing distorted audio on FM but the signal otherwise seems “quiet”, it might be due to overmodulation or overdeviation - try talking a little quieter or further away from the mic.

So there you have it - FM in a nutshell. It’s user-friendly, clear, and perfect for local chats. Whether you’re ragchewing with a buddy across town or checking into a local net, FM is likely to be your mode of choice. Happy chatting, and remember - keep it friendly, keep it clear, and most importantly, have fun!