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Radar Detector Breakdown

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New for June 2020, thanks to Hadrien! By studying commercial microwave products you can learn how to minimize cost. Enjoy!

 - Unknown Editor

Radars are used by forces of order in order to measure the speed of drivers to punish them when they exceed the maximum allowed speed. It is tempting to use radar detectors to detect radars in order to be able to drive at higher speeds than allowed and still be able to slow down just before the radars to avoid the sanction. However, keep in mind that in some states and countries, use and even the mere owning of such devices can lead to penalties. At least in France, when the device is permanently integrated in the vehicle, the whole vehicle can be seized! So, is saving a few minutes worth risking both your live, penalties and even your car?

Additionnally, it's worth remembering that driving can be dangerous (see https://www.microwaves101.com/put-down-the-cell-phone) and must be done in a careful manner.

Before unmounting the device, here are the pictures of the still whole device:

Top side Underside

Here are views of the radar detector unmounted:

A bit unmounted... A little more...

The device contains an horn antenna, to receive the waves, some photodiodes or phototransistors to detect lidars, some processing electronics, a cover under which a speaker is fastened, a red PCB on the back side with a display and the buttons, and transparent red pieces of plastic on the back and front side of the device.

The top side red PCB is as follows:

It's worth mentioning that the display shows the types of signals detected. X, Ku, K, and Ka are for the microwaves. L is for the lidar, outside of the topic of this page. However, the function of the other letters is not clear without the user manual. There is no user manual available on the web, but according to a website, the detected bands are the following :

Band Frequency
X 10.525 GHz +/- 0.100 MHz
Ku 13.450 GHz +/- 0.125 MHz
K 24.150 GHz +/- 0.175 MHz
Ka 33.400 GHz +/- 1.300 MHz

The detected microwave frequencies span a range from 10.425 to 34.700 GHz. Such a wide range forces the use of a broadband antenna, the horn, as well as a broadband frontend.

The bottom side of the PCB is as follows:

It contains an USB connector, whose function is not very clear, maybe for firmware update or as a power supply; a round connector for the 12 V 300 mA supply; a push button; a cable with black and red wires, connected to the speaker; a cable with black, yellow, and red wires; and some other components.

The chip near the speaker wires is labelled "DRSL241502P16". A web search and automatic translation shows immediately that this chip is a vocal chip. The manufacturer on its website (http://www.fbiic.com/news/news94.html, http://www.fbiic.com/product/product97.html) claims that it has an integrated "1024 bit" "encryption" which is "impossible to break" to prevent "plagiarism". Which is a bit funny claim for a product for a chip from China. Since it is a Chinese product, given their local laws, it can be guessed that at least China can break the encryption. Beside that, are the few seconds of voice telling the driver that he must "slow down" really worth encryption ? This voice is clearly not the hard part of the design.

The most interesting and complex part is the RF design. Here are the pictures, starting from the antenna:

After further opening:

The antenna is integrated with the metal enclosure of the electronics. This is not for the faint of hearth, both electrically and mechanically. This antenna is a ridged horn antenna, the most suited for the job: wideband and convenient to integrate with a PCB. Note the way the ridge touches the PCB. There is no such thing as a probe like in some other designs.

Close-up on the ridged part:

The assembly of the two boards can be further unmounted. There is a clear separation between the high frequency part, which must be manufactured on a microwave substrate because FR-4 would be much too lossy at such frequencies (max 34.7 GHz), and the low frequency parts which can be manufactured on standard FR-4. Both board are separated by the shielding enclosure and connected by square pin connectors. The shielding of the high frequency part is interesting to prevent perturbation from non interesting signals from the outside.

The high-frequency part is shown in more detail on the following picture:

Starting from the right, the ridge is in contact with the trace on the right side of the board, allowing transmission of the signals. Coupled lines are used as a DC block. This is a very clever design, allowing to avoid the use of high frequency capacitors.

 

 

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Author : Hadrien Theveneau

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