First comes the furrowed brows. Then perhaps a frown or two. At last, a hesitant hand goes up. “I don’t get this whole mode thing.”
“Yea, me either,” follows a comforted chorus, each student relieved that it’s not just them having a little trouble.
It never seems to fail to confound the beginner studying for the Technician Class license – modes. In the Technician Class that I teach regularly along with several other experienced hams it is always the subject of many questions and the source of puzzled expressions. Couple an introductory discussion of modes with frequency bands or signal bandwidth topics and you’ll mostly get slowly shaking heads.
So, let’s carefully dissect this matter of modes, disentangle the terms and the implications, and provide a few solid examples that we can all latch onto. Then we’ll sprinkle in the relationships with frequency and bandwidth. Afterwards you’ll be ready to answer those puzzled looks emanating from your fellow newbies!
What’s a Mode? The term “mode” really has two meanings in ham radio. The two different meanings are often scrambled together in conversation, and the definitions do overlap somewhat. It boils down to whether you are referring to a type of general radio operation or to a specific type of signal modulation, as follows:
Operating Mode – An operating mode is a description of what you, the operator, are doing to send and receive signals. For example, the term “phone” refers to using your voice on the radio. Hence, you will hear hams referring to “phone mode” or “the phone modes,” meaning an operation in which the operator is speaking into a microphone and pumping voice signal out over the airwaves. Other general operating modes include the digital modes and video modes. In digital modes you are using a computer (or other electronic device) to send encoded signals, and in video modes you transmit and receive specially formatted video stream signals.
Key concept here: An operating mode may be carried out with one or more individual modulation modes.
Modulation Mode – A modulation mode refers to the specific method by which information is encoded into the radio emissions. For example, a transceiver may affect frequency modulation (FM), amplitude modulation (AM), or single sideband modulation (SSB) to encode your voice into the radio transmission. Each of these three modulation modes (FM, AM, SSB) may be used with the phone operating mode. Another example: PSK31, Packet Radio, Radio Teletype (RTTY), and Multiple Frequency Shift Keying (MFSK) are specific modulation modes that can each be implemented with, or characterized as, a digital operating mode. Usually continuous wave (CW) is lumped into the digital modulation mode category as well, even though it is unique as a manually implemented operating mode using a key to tap out Morse Code signals.
Operating Mode | Modulation Modes |
Phone | FM, AM, SSB, [and others] |
Digital | PSK31, Packet, RTTY, MFSK, JT-65, FT-8 [CW], [and others] |
Video | Slow Scan TV (SSTV), Fast Scan TV (FSTV – NTSC standard) |
CW | CW |
The table above is a somewhat simplified view of operating modes and the affiliated modulation modes. But sometimes things get scrambled together a little more. For instance, there are digital phone modes. That is, your voice is converted into digital signals to be transmitted by a digital modulation method over the air. The ICOM D-STAR mode and DMR (Digital Mobile Radio) are two examples of digital phone. Computer software is available that will encode and decode CW for you, allowing you to use a computer keyboard and monitor to send and receive Morse Code by CW modulation mode. This may be characterized as a blend of a digital operating mode with CW modulation mode.
What’s Modulation? The operating mode concept is pretty easy to grasp – you are typically speaking into a microphone, tapping out some code, or keying a computer. But modulation modes are a little more ethereal to us since it involves manipulation of invisible and strangely behaving radio frequency waves of electromagnetic radiation. So, let’s get a refresher on the different types of modulation mentioned in the preceding discussion.
Amplitude Modulation encodes a signal into the RF waveforms by changing the amplitude (power) of the RF waveforms, as depicted in the figure to the right. The top waveform in blue is an input audio signal, perhaps generated with your microphone. In the transmitter’s modulation circuits the relatively low frequency (long wavelength) audio signal is imposed on the much higher frequency (shorter wavelength) radio waveforms. The radio frequency (black waveform) amplitude is conformed to the varying amplitude of the audio signal. The RF signal is transmitted with variable amplitude, as in the bottom figure, with the audio signal waveform shape riding along in the amplitude variations. The receiving station demodulates the RF waveform, reproducing the lower frequency audio signal from it to drive a speaker.
This is the modulation mode AM. The modulation mode Single Sideband (SSB) is a specialized, highly efficient form of AM, but the basic concept of amplitude modulation is the same with SSB.
Frequency Modulation encodes the audio signal by deviating the frequency of the RF rather than the amplitude. The next figure compares AM modulation with FM modulation for the same audio input signal. Notice how the FM amplitude is unvarying, but the frequency increases and decreases with the input audio amplitude. This is the modulation mode FM, used by your HT and most repeater systems to encode your voice and transmit it over the air.
Continuous Wave (CW) encodes signals simply by turning the transmission on or off in patterns of Morse Code. With CW there is no manipulation of the waveform amplitude or frequency – the wave is continuous, only interrupted by the operator in patterns to encode characters. Each ‘dit’ and ‘dah’ of Morse code is produced by a brief transmission of unvarying RF emission, with about a 3:1 ratio of the emission duration, ‘dah’ to ‘dit.’
Digital Modes use several unique modulation methods, from shifting the phase of an RF waveform between two or more relative states, to transmitting two or more different tones in on-off sequences for encoding characters, to other schemes. Each specific digital modulation mode has unique characteristics, performance, and operating mode activities. You can learn more about the specifics of digital modulation modes in the HamRadioSchool.com Technician License Course book and from the ARRL.
How Do Frequency Bands and Bandwidth Relate? First, let’s quickly refresh the beginner on just what constitutes a band and bandwidth.
A band is a contiguous range of frequencies used by radio operators to send and receive signals. The FCC Amateur Radio Band Plan defines the specific bands of frequencies available to hams. Frequency bands are designated by their associated approximate wavelength. So for instance, the band from 50.0 to 54.0 MHz is called the “6-meter band” (6m) because the wavelengths in that frequency range are all about 6 meters long.
And further, the width of those bands in units of hertz (Hz) or megahertz (MHz) is its bandwidth. So, the 6m band has a bandwidth of 4 MHz: 54.0 MHz – 50.0 MHz = 4.0 MHz. The same concept of bandwidth applies to a narrower radio transmission. A small band of frequencies is used by a transceiver to send and receive any radio message, typically from a few hundred hertz to several thousands of hertz. The bandwidth needed for a transmission depends on the modulation used.
It is important for the new ham to understand that any operational mode and any modulation mode is technically usable on any of the amateur frequency bands. So, it is feasible to operate phone mode FM on the 70 cm band, on the 2m band, on the 6m band, and lower frequency bands. It is feasible and quite popular to use SSB on any of those same bands. It is also feasible to use CW or digital modulation modes across those same frequency bands. Modes and bands are completely distinct concepts! Any mode may be coupled with any band… strictly technically speaking.
However, a prominence of some modes over others has evolved across the bands for very practical reasons, not the least of which is the consideration of bandwidths required by the different modes. As such, some bands tend to be mentally associated with particular modes more than others. This is why the confusion between modes and bands tends to crop up with the beginner ham, along with the fact that an operational mode, a modulation mode, a particular frequency band, and a bandwidth comment may all be squished together in a single statement by the typical gray beard elmer!
Here is how some of the frequency bands and modes tend to shake out together, keeping in mind this is a grand generalization and that many modes are used across all the amateur frequency bands.
For practical reasons of spectrum use the FCC restricts FM to the 10m and higher bands only [10m, 6m, 2m, 1.25m, 70cm, and shorter wavelength bands]. Frequency modulated phone tends to use up a broad, continuous swipe of the spectrum (large bandwidth), and it is not practical with the limited spectrum allocations of the lower HF bands [12m, 15m, 17m, 20m, 30m, 40m, 60m, 80m, 160m bands]. But phone mode using SSB is very popular on the lower HF bands, as it uses much less bandwidth than FM and there is enough room to accommodate many operators across the FCC’s band allocations. Additionally, SSB is significantly more power efficient for long distance, weak signal propagation conducted on the HF bands. For these reasons, SSB modulation mode is most associated with the HF bands for phone. FM is most associated with the VHF and UHF bands for phone operations and repeaters since local operations are not ‘weak signal’ situations and more bandwidth is available in the VHF and UHF bands for the wider bandwidth FM signals. But, SSB modulation is also used in the VHF and UHF bands for phone operations, especially for contesting on the 6-meter, 2-meter, 1.25-meter, and 70-centimeter bands.
The CW mode is usually associated with the HF bands more than the VHF or UHF bands. The HF bands promote long distance contacts (DX) around the world with low power, so CW is very popular on the HF bands. However, many operators also use CW on 6m and higher VHF/UHF bands, especially during contests and special event station operation.
Digital modes of various types are used extensively on HF to UHF, and beyond. The digital modes used predominantly on the HF bands tend to be narrow bandwidth methods such as PSK31, RTTY, MFSK, and various JT-modes (JT-65, FT-8, others).
The chart below is a summary by KØNR of the most common modes on each of the amateur bands. Note, this chart is not all inclusive but only points out the most popular mode-band parings.
Does this statement make sense to you now?
“I really like SSB phone on 6m, or CW on 10m, but there lot’s more traffic on 2m FM, so I hang out on the repeaters more than anything.”
Notice how the modulation modes and operational modes are mixed together or simply implied by the band-modulation combination (as in 2m FM). But now you can keep it all straight no matter how tangled up the terms!
I hope this helps you to avoid the furrowed brow, the frown, and most confusion over the loads of modes, and the frequency bands, and the bandwidth considerations that tend to impact their combinations. It’s not nearly as confusing as it first sounds when listening to experienced hams jawing about their various operations.
Good luck with your studies! 73
~ Stu WØSTU