Ham radio in the 21st century

Doug Grant, K1DG -November 04, 2011

Ham radio in the 21st century figure 221st century equipment
Licensed amateurs can transmit in bands in the LF, MF, HF, VHF, UHF, and microwave bands. With a good antenna, amateurs' equipment can achieve worldwide communications on many of these bands.

Most amateurs buy their equipment from stores. Years ago, the best-known brands were mostly US companies, such as EF Johnson and Heathkit and the now-defunct Collins, Hallicrafters, and Hammarlund. Ham radio in the 21st century figure 3Today, the most popular brands are mostly Japanese companies, including Icom, Kenwood, Yaesu, and Alinco (Figure 2). A few US manufacturers, such as Elecraft and FlexRadio, have entered the market in the past decade (Figure 3), and the first Chinese-made transceivers are beginning to appear, from manufacturers such as Wouxun.

The technology used in ham equipment has evolved significantly. Most high-performance HF/VHF transceivers now use digital-signal-processing technology for at least some of the modulation, demodulation, and filtering functions. A careful partitioning of both analog- and digital-signal processing achieves the best performance, and today’s radios offer excellent sensitivity and 100-dB dynamic range, with digital-signal-processing-enabled selectivity. Although most radios still maintain the traditional format of a front panel with a large knob to control the frequency and lots of other buttons and knobs, some newer SDRs (software-defined radios), such as those from FlexRadio, abandon this tradition in favor of keyboard and mouse operation; they have no front-panel controls (Figure 4).

Ham radio in the 21st century figure 4Handheld VHF FM transceivers have evolved to include multiband operation, embedded GPS, spectrum-analyzer displays to show signals on adjacent frequencies, and even Bluetooth. None have yet reached the level of sophistication of smartphones, but touchscreen-driven radios and Internet connectivity cannot be far off. Speaking of smartphones, hundreds of ham-radio apps are available for these devices, ranging from license-prep courses to satellite tracking to remote-station control.

However, not all hams buy their equipment off the shelf. Some prefer to build their own equipment. Ham operators have always been enthusiastic tinkerers, often building their equipment from discarded pieces of consumer electronics they find in their neighborhoods. Many hams understand concepts such as intermodulation distortion and phase noise, for example, because they have heard the effects of these signal imperfections, and they understand what happens when a nominally linear power amplifier enters hard compression.

Home-brewed radios can range from extremely simple transmitters and receivers to true state-of-the-art SDR systems. At the low end, one creative ham disassembled a compact fluorescent light bulb and discovered a high-speed, high-voltage switching transistor and assorted capacitors and inductors. By adding a 3.579-MHz TV colorburst quartz crystal, which sits conveniently in the middle of the 80m amateur band, he was able to construct a 1.5W CW transmitter from the parts (Reference 2).

Ham radio in the 21st century figure 5Simple receivers are also easy to construct. Ham operator Charles Kitchin has developed a series of super-regenerative receivers that are easy to build and that work surprisingly well (Reference 3).

The work of the High-Performance Software-Defined Radio Organization is at the cutting edge of radio design. This group has collaboratively developed a series of modules that use the latest high-performance components, including the RF amplifiers, mixers, ADCs, DACs, processors, and memory. For example, the Mercury receiver module enables direct sampling of the 0- to 65-MHz spectrum, using a 130M-sample/sec, 16-bit ADC and an FPGA to undertake digital downconversion. Open-source software performs all of the signal-processing and control functions, and the hardware also supports third-party software (Figure 5).

An engineer interested in developing his own SDR radio can build or buy an RF front-end/quadrature downconverter and connect it to the audio input of a PC and buy or write appropriate software for the demodulation and detection functions. Connecting the baseband in-phase and quadrature outputs of the radio to the left and the right inputs of the PC completes all of the hardware work. Some hams have constructed SDR front ends in the form factors of USB memory sticks and draw their power from those sockets.

Ham radio in the 21st century figure 6For those more inclined toward classic analog-radio design, OpenQRP is an interesting project. “QRP” is a ham abbreviation for low-power transmitter (Figure 6). The creator of the group, Steve Elliott, call sign K1EL, has developed an open-source hardware and software design for a simple low-power CW transceiver. He uses an Atmel microprocessor in the popular Arduino prototyping platform for the human interface and various control functions and provides a PCB and complete kit of parts. Elliott documented his trial-and-error design as it evolved, and his blog serves as an excellent tutorial on radio design (Reference 4).

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