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Review by Allan Linton-Smith This handy little radar speed detector has enough sensitivity to detect the speed of tennis, cricket, baseball, softballs and footballs. It’s also useful for checking the speed of your golf swing, running or even your car. Radar Coach how fast can you run, bowl, serve, kick or drive? T he Radar Coach is available from Tennis Warehouse Australia for $249, including GST and delivery (www.tenniswarehouse.com. au/radar-coach-speed-gun.html). It comes with a small tripod and carry case and is specifically marketed toward tennis players, to help them improve their serving. But as mentioned above, it will work well for all sorts of applications. We don’t usually review this kind of product, but we were surprised by how well it worked and thought some of our readers would be interested in it. The Radar Coach has a large display made of 5mm LEDs behind a translucent housing. The little holes at the bottom are for the loudspeaker, which can be set to announce the speed (in an American accent) in case the display is obscured, and it is remarkably loud. It can also discriminate between the ball speed and the running speed of the bowler or pitcher. The display is 165 x 120mm and the numerals are 60mm high. These look like big 7-segment LEDs but, as mentioned, are made of standard 5mm LEDs. The result is pretty effective. The display is easily visible in sunlight and flashes the speed for a few seconds. It gives you the option to display (and possibly also announce) the measured speed in km/h or mph. One possibly helpful application for the audible speed readings is for race marshals, who can listen for vehicle speeds as they enter the pits without taking their eyes off the track. The manufacturer recommends that the device be put behind a wire fence to prevent damage from fastballs, because it is only housed in a plastic case that could crack if it’s hit hard, especially by a cricket ball. As fencing may obscure the visual readout, the voice message is again helpful. It can record the last ten readings. I like that it can ignore your running speed (such as running up to the cricket pitch) and only detect the ball speed. It does this by assuming you can’t run more than 45km/h and sets this as the minimum activation speed. Usain Bolt tops out at 44.72km/h, so that’s a pretty safe assumption. The circuitry From the outside, I could not see an opening for the radar transmit/ receive pads or antennae, so I opened it up to have a look. Inside, I found a radar module labelled “MC420S-G 10.525 GHz”, which looks a lot like the MDU2750 from Microwave Solutions that I am familiar with. Unfortunately, I couldn’t find any data on the MC420S-G, but it could just be a re-badged MDU2750. These operate from a 5V DC supply, transmit a chopped 10dBm (10mW) signal at 10.525GHz and are accurate to within 0.03%. They use a dielectric resonator stabilised FET oscillator, which provides stable operation over a broad temperature range in either CW or low duty cycle pulsed mode, and a balanced mixer for good sensitivity and reliability. Features & Specifications ∎ Accurate readings of speeds up to 199km/h or 150mph ∎ Easy-to-read numbers ∎ Voice reading can be turned on or off ∎ Portable with free-standing or hand-held use ∎ Ideal for tracking tennis serve and ground-stroke speed ∎ Can measure ball speed or swing speed ∎ Set up on the ground behind a net (for protection) on in-built legs, or use your own tripod for more height ∎ Includes carry case ∎ Powered by 5 AA cells (not included) ∎ Record button repeats the last 10 readings 38 Silicon Chip Australia's electronics magazine siliconchip.com.au They are a type of Doppler radar that detects the frequency shift between the transmitted and reflected signal from a moving object. The mixer produces a low-level signal which contains a signal at the difference frequency between the transmitted and received signals – see Fig.1. The frequency of this signal indicates the speed of the moving body. This low-frequency signal is filtered out, amplified and processed to provide an audible and/or visual speed. The 10.525GHz radar module draws 60mA from a 5V supply and produces a 700Hz output signal for an object approaching at 36km/h. The MDU2750 has a frontal range of approximately 50 metres and a rear range of only 2-3 metres. This unit functions from -30°C to +70°C, but performance may be degraded above 55°C. In the Radar Coach, the radar transmitter is behind a plastic panel, separated by a 2mm-thick piece of rubber. This presumably attenuates the signal somewhat, and we estimate the usable The internals of the Radar Coach. The 10.525GHz radar module is at the top and has a four-patch antenna arrangement. It runs from 5V DC and transmits at 10mW, sufficient to penetrate the plastic housing. Note the small 8W loudspeaker at the bottom for announcing the speed. range to be around 6m. It also depends on the size and reflectivity of the target. Note that it will be inaccurate if an object approaches the detector at an angle. Imagine a ball going diagonal to the radar beam; the detector will only calculate the approach speed, which is considerably lower than the actual speed; 30% low for a 45° angle. So balls should be aimed directly at the device without actually hitting it (hence the recommendation to put it behind a fence). Conclusion The Radar Coach is considerably less expensive than other similar devices we’ve seen, which often cost several thousand dollars. Despite this, it does not compromise accuracy. It seems to achieve this by using a low-cost mass-produced radar module originally designed for automatic Fig.1: the basic arrangement of the Doppler radar module. The oscillator generates a very highfrequency RF signal that’s sent out via the transmitting antenna. The frequency-shifted received signal is mixed with the original signal to produce a difference signal that becomes the IF (intermediate frequency) output. This is filtered, amplified and processed to generate a speed reading. The Radar Coach is ideally located behind a wire fence to protect it from being hit by the ball. Its large display uses 5mm LEDs behind a translucent housing which gives a readable display in full sunlight. The little holes at the bottom are for the loudspeaker. siliconchip.com.au doors, plus a very cost-effective processor, display and audio amplification design. The tripod mounting system is preferred over a radar gun arrangement because it does not require a coach to point, measure and call out each speed reading. It really does replace a coach in that sense (but won’t give you any tips!). Overall, this device is fun to use and is much cheaper than any direct equivalents I can find. If you’re having trouble getting accurate readings, keep in mind that it’s critical that you set it up properly. As for its build quality, I gave it to my grandson and he has dropped it several times, hit it many times with balls and it still works a treat. He is a fast bowler and It has helped him enormously with his wicket-taking. He is SC the fastest on his team now! Australia's electronics magazine June 2022  39