This is only a preview of the June 2022 issue of Silicon Chip. You can view 41 of the 112 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "Spectral Sound MIDI Synthesiser":
Items relevant to "Buck-Boost LED Driver":
Items relevant to "Arduino Programmable Load":
Items relevant to "500W Power Amplifier, Part 3":
Items relevant to "MOS Air Quality Sensors":
Items relevant to "Revised Battery Charge Controller":
Purchase a printed copy of this issue for $11.50. |
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
|