Cheap generic K-band OEM radar for ALPR review

We are experimenting with different radar types to complement our automatic license plate recognition (ALPR) camera.

So far we have worked with DR1500 from Houston Radars. That unit is too powerful for an ALPR application. The can reads  license plates at the range of 10 … 30m so there is no point in measuring speed 200m away.

The other problem we encountered with the DR1500 is that it’s impossible to say what it is measuring – a truck at 150m, a van at 100m or a car at 30m if they are all in the view of the radar at the same time. A simpler and smaller radar, limited to about 50m gives us all the info we need.

We purchased a sample from this AliExpress store for a test, but you can buy it from many other sellers on AliExpress or Alibaba.

K-Band OEM Radar Spec

Model: CFK401A1T1R-V3

Brand: Doisyen (?)

Power consumption: 58mA x 12.6v = 0.73w (measured with a multimeter)
There was no change in power consumption during operation. Changing the output interval didn’t affect the power consumption either. I expected the RF emission duty cycle to go down with a longer interval between readouts.

The unit gets quite warm, most of it around the antenna. This is why they have such a big heat sink underneath it. Consider using active cooling in hotter climates.

Conformal coating: none.

Controls and indicators: a single red LED when ON. No blinking or any other indication of any type of activity – it’s just on.

Size: 48mm x 48mm x 30mm (including the connector with wires)

 

Technical details

This part was copied from their official technical spec, so take it with a grain of salt.

  • Speed range: 1 … 240km/h
  • Accuracy: +/- 1km/h (shouldn’t it be percentage? is it temp compensated?)
  • Detection distance: > 100m
  • Voltage: 9 – 24VDC
  • EPIR: 15 … 22 dBm, 18dBm typ (emission power?)
  • Working temp: -40 … 75°C
  • Beam: 18° horizontal x 40° vertical
  • Frequency: 24.15GHz centerband
  • Radar type: FSK/CW (Frequency Shift Key / Continuous Wave)
  • Interface: RS232 /RS485

CE, FCC, RoHS, UL – there is no mention of any official certification, but the solder looked lead-free. The components may still contain lead.

Pinout

[V] – Vin, DC 9v … 24v
[G] – ground
[G] – ground
[R] – RS232 Rx
[T] – RS232 Tx
[G] – ground
[B] – RS485 B
[A] – RS485 A

Communication protocol

I used Hercules SETUP utility by HW-group.com to read from / write to the radar via an RS-232 port.

Connection: 9600baud, 8 bit, parity None, handshake Off, mode Free.

Try the following 3 commands. A correct command returns Set OK response. An incorrect command returns nothing.

0x43 0x46 0x01 XX YY ZZ 0x0d 0x0a

  • XX: minimum reported speed, default 0x01
  • YY: angle compensation of the radar beam to the car trajectory, expressed in degrees, default 0x00
  • ZZ: radar sensitivity, 0x00 … 0x70, default 0x00

Example:

0x43 0x46 0x01 0x0a 0x0f 0x40 ox0d 0x0a

10km/h min speed, 15° angle to the vehicle trajectory, average sensitivity

Notes on sensitivity:

0x00 – the radar was so sensitive that even moving my fingers at 50cm gave me 1 … 5kmh readouts, but it actually worked OK outside with trees swinging in the distance (50m+). It did give me about 100m range for a family-sized car.
0x10 – not sensitive to fingers, but a band of rain produced a barrage of random speed readouts
0x40 – approx 50m range for the average car, 150m for a truck
0x60 – 30m … 50m range

0x43 0x46 0x02 MM TT UU 0x0d 0x0a

  • MM: 0x00 detect both directions, 0x01 incoming only, 0x02 outgoing only, default 0x00
  • TT: interval between speed readouts, default 0x00 for approximately 22 per second, increasing up to once per second with the increase in TT value
  • UU: 0x00 for km/h, 0x01 for mph, default 0x00

Example:

0x43 0x46 0x02 0x01 0x50 0x00 ox0d 0x0a

incoming only, 3 readouts per second, km/h

The mode (MM) can have a value of 0x03 for “metering test mode with anti-vibration switched off”.

Setting the interval (TT) to 0x50 gave me approximately 3 readouts per second.

0x43 0x46 0x03 VV 0x00 0x00 0x0d 0x0a

  • VV: anti-vibration, 0x00 … 0x70, default 0x00

The higher the value the more immune it is to vibrations, but the radar may miss brief movements. I have not tested this setting as vibration was not a concern for our ALPR setup. Given that a vehicle is likely to be in the view of the radar for some time it is safe to set a higher value.

Sample radar output

It just outputs the values at a set interval if there is a moving object. “+” for incoming, “-” for outgoing, “#” – denotes a speed digit

Incoming vehicles: V+###.#{0D}{0A}
Outgoing vehicles: V-###.#{0D}{0A}

Example:

V+003.5{0D}{0A}V+004.0{0D}{0A}V-002.5{0D}{0A}V-002.5{0D}{0A}V-004.0{0D}{0A}V-004.5{0D}{0A}V-005.5{0D}{0A}V-003.5{0D}{0A}V+002.0{0D}{0A}V+001.5{0D}{0A}V+001.0{0D}{0A}V+003.0{0D}{0A}V+001.5{0D}{0A}V+005.0{0D}{0A}V+005.0{0D}{0A}V+004.5{0D}{0A}V+004.0{0D}{0A}V+004.0{0D}{0A}V+002.5{0D}{0A}V+003.0{0D}{0A}V+002.5{0D}{0A}V+002.0{0D}{0A}V+002.0{0D}{0A}V+002.5{0D}{0A}V+002.5{0D}{0A}V+001.0{0D}{0A}V+002.5{0D}{0A}V-027.7{0D}{0A}V-029.7{0D}{0A}V-034.2{0D}{0A}V-034.7{0D}{0A}V-036.8{0D}{0A}V-036.8{0D}{0A}V-037.3{0D}{0A}V-036.8{0D}{0A}V-034.2{0D}{0A}V-034.7{0D}{0A}V-036.8{0D}{0A}V-039.3{0D}{0A}V-040.8{0D}{0A}V-042.3{0D}{0A}V-043.3{0D}{0A}V-044.3{0D}{0A}V-044.3{0D}{0A}V-044.3{0D}{0A}V-044.3{0D}{0A}V-043.3{0D}{0A}V-041.8{0D}{0A}V-041.3{0D}{0A}V-040.8{0D}{0A}V-033.7{0D}{0A}V-034.7{0D}{0A}V-036.8{0D}{0A}V-037.8{0D}{0A}V-038.8{0D}{0A}V-039.3{0D}{0A}V-039.8{0D}{0A}V-040.8{0D}{0A}V-041.3{0D}{0A}V-041.3{0D}{0A}V-041.8{0D}{0A}V-042.3{0D}{0A}V-042.8{0D}{0A}V-042.8{0D}{0A}V-043.3{0D}{0A}V-043.3{0D}{0A}V-043.8{0D}{0A}V-044.3{0D}{0A}V-044.3{0D}{0A}V-044.8{0D}{0A}V-044.8{0D}{0A}V-044.8{0D}{0A}V-044.3{0D}{0A}V-043.8{0D}{0A}V-043.3{0D}{0A}V-042.8{0D}{0A}V-041.8{0D}{0A}V-040.3{0D}{0A}V-033.7{0D}{0A}V-033.2{0D}{0A}V-030.2{0D}{0A}V-028.2{0D}{0A}V-026.2{0D}{0A}V+037.3{0D}{0A}V+037.3{0D}{0A}V+037.3{0D}{0A}V+038.3{0D}{0A}V+039.3{0D}{0A}V+041.3{0D}{0A}V+041.3{0D}{0A}V+042.3{0D}{0A}V+042.8{0D}{0A}V+043.3{0D}{0A}V+043.8{0D}{0A}V+044.3{0D}{0A}V+045.3{0D}{0A}V+045.8{0D}{0A}V+047.4{0D}{0A}V+048.4{0D}{0A}V+049.4{0D}{0A}V+050.4{0D}{0A}V+051.9{0D}{0A}V+052.9{0D}{0A}V+053.9{0D}{0A}V+054.9{0D}{0A}V+055.4{0D}{0A}V+055.4{0D}{0A}V+055.4{0D}{0A}V+053.9{0D}{0A}V+051.9{0D}{0A}V+050.9{0D}{0A}V+037.8{0D}{0A}V-017.6{0D}{0A}V-019.1{0D}{0A}V-023.1{0D}{0A}V-022.6{0D}{0A}V-026.2{0D}{0A}V-026.2{0D}{0A}V-027.2{0D}{0A}V-027.7{0D}{0A}V-027.7{0D}{0A}V-028.2{0D}{0A}V-028.2{0D}{0A}V-028.2{0D}{0A}V-028.2{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-028.7{0D}{0A}V-029.2{0D}{0A}V-029.2{0D}{0A}V-029.2{0D}{0A}V-029.7{0D}{0A}V-029.7{0D}{0A}V-029.7{0D}{0A}V-029.7{0D}{0A}V-030.2{0D}{0A}V-030.2{0D}{0A}V-030.7{0D}{0A}V-031.2{0D}{0A}V-031.7{0D}{0A}V-031.7{0D}{0A}V-032.2{0D}{0A}V-033.2{0D}{0A}V-033.7{0D}{0A}V-034.2{0D}{0A}V-034.2{0D}{0A}V-035.3{0D}{0A}V-036.3{0D}{0A}V-036.3{0D}{0A}V-037.8{0D}{0A}V-044.8{0D}{0A}V-047.9{0D}{0A}V-054.9{0D}{0A}V-058.5{0D}{0A}V-059.0{0D}{0A}V-059.5{0D}{0A}V-059.0{0D}{0A}V-059.0{0D}{0A}V-058.5{0D}{0A}

 

Conclusion

  1. It is cheaper than Houston Radar and other western brands. We paid US$375 for one unit, but the price goes down to US$250 for larger quantities.
  2. It does the job for the short range speed detection required for automatic number plate recognition.
  3. It is a power hog compared to Houston Radar SS400.
  4. It is probably illegal to use this radar given the absence of FCC / CE certification for this RF emitter.

 

Use at your own risk.