Spring 2007 Issue

PROPAGATION

Trends, Reflections, and an Outlook

By Tomas Hood, NW7USA

This is the Koch Method CW Trainer by G4FON. Notice all of the extra features that help you
build your skill. See text for links to information regarding the Koch method of Morse code training. (Source: NW7US, using the the
software by G4FON)

With the removal of the requirement to pass a Morse code exam in order to obtain an FCC-issued amateur radio license, you’d think that Morse code might fade into the dim light of history. However, amateur radio operators who are passionate about VHF weak-signal operation use the CW mode to accomplish those challenging communications. When we talk about the propagation of VHF, UHF, and smaller wavelength radio signals, we include modes of propagation that require alternatives in how the “intelligence” (voice, data, or simply our side of the conversation) is embodied (the protocol or mode) in the signal.

One of the many driving goals behind the research and experimentation in the science of radio-signal propagation is purely the desire to obtain efficient communications between two stations. Often when people talk about radio reception, signal strength is touted as the most useful factor in the effort to get a signal from the transmitter to the receiver. However, since the problem of reception is more complex than simply a power issue (just pump more watts into the antenna), the better way to get a handle on the problem is to use the signal-to-noise ratio (SNR) measurement of a radio circuit. (The radio circuit is the path between, and including, the transmitter and receiver.) The SNR is a real measure of effectiveness. With it, we can better understand how effectively a signal can get from point A to point B.

On an abstract numerical basis, the signal-to-noise ratio is inversely proportional to the width of the slice of frequencies in which we are detecting our signal. This slice is also known as the bandwidth we are receiving, and that bandwidth contains the intelligence we’re trying to detect. A slice that is 10 Hz wide (we can also call this a 10-Hz channel) would give a signal-to-noise power advantage of 23 dB, or 210 times greater in strength than the level of inherent noise in a 2100-Hz channel (a typical bandwidth for single-sideband [SSB] voice communication).

In simplified terms, that means a signal that is transmitted with 1 watt in a very narrow 10-Hz wide channel is 210 times more efficient than a 1-watt (fully-modulated) SSB signal. Imagine the improvement you would get on your FM signal between your radio and a distant radio if you changed your antenna so that you would have a gain of 23 dB. That’s like going from 5 watts to just over one kilowatt.

When we talk about using modes such as CW, we are interested in how effective that mode is compared to other modes. Again, when we want to get our VHF signal from point A to point B over long distances, perhaps by bouncing the signal off the moon, we want to find the most efficient modes and concentrate our signal propagation efforts on those modes. Over such great distances the signal will experience loss. The more “power” it has, the more chance we’ll “hear” it on the receive side of that long journey.

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