1. ## In Nitty-Gritty Detail, How Do Radar Detectors Work?

I'll throw out a theory and you tell me if I'm correct:

A Radar Detector is a lot like a police scanner in "search" mode: it has a computer-controlled radio receiver that can rapidly step through an entire range of frequencies, pausing briefly on each one to see if there is an RF carrier present. If there is, it pauses briefly on that frequency and does some additional analysis; if it determines that this is, in fact, a real radar signal, it begins sounding an alert, then continues scanning.

Assuming the above is correct, do we have any idea as to what the step size is (i.e. the difference in frequency between one hop and the next), how long it takes to tune to a new frequency, how long the dwell time is on each one, etc.? I read one estimate which said all three police radar bands could be scanned in under one second. Compared to a police scanner that can do maybe 40 frequencies per second that's amazingly fast! How do they manage it?

2. ## Re: In Nitty-Gritty Detail, How Do Radar Detectors Work?

Originally Posted by swarga
I'll throw out a theory and you tell me if I'm correct:

A Radar Detector is a lot like a police scanner in "search" mode: it has a computer-controlled radio receiver that can rapidly step through an entire range of frequencies, pausing briefly on each one to see if there is an RF carrier present. If there is, it pauses briefly on that frequency and does some additional analysis; if it determines that this is, in fact, a real radar signal, it begins sounding an alert, then continues scanning.

Assuming the above is correct, do we have any idea as to what the step size is (i.e. the difference in frequency between one hop and the next), how long it takes to tune to a new frequency, how long the dwell time is on each one, etc.? I read one estimate which said all three police radar bands could be scanned in under one second. Compared to a police scanner that can do maybe 40 frequencies per second that's amazingly fast! How do they manage it?
I don't know the exact answers, but I think its more accurate to say the 1st Lo sweeps a range vs steps like a scanned. Remember old AM/FM radios where you turned a dial to get to the exact frequency? It more like that. Here is an ancient article, but it gives some details and block diagrams. Also included is a review of a Whistler from Mem-Tek with some discussion of the construction and circuitry

http://servv89pn0aj.sn.sourcedns.com...Conversion.pdf

MEM-TEK's Whistler Pro78 Review

3. ## Re: In Nitty-Gritty Detail, How Do Radar Detectors Work?

One big difference between a scanner and a RD: A scanner uses a frequency synthesizer circuit that "jumps" from frequency to frequency as it scans. An AM/FM radio with a digital tuner is the same way, it tunes at specific intervals (e.g. 100 or 200 KHz intervals for FM).

A RD uses a Voltage Controlled Oscillator (VCO) that can sweep in a continuous fashion. Thus it can scan a range of frequencies without skipping anything "in between". RDs need to do that since radar guns can drift off the exact frequency that they are tuned to.

RDs are also designed to be able to sweep very quickly, especially in the superwide Ka band. In most cases, they don't "stop" on a frequency like a scanner does when it picks up a signal (One exception is Cobra, who can "park" their LO on a specific frequency to analyze a signal... this is a lot of the reason why Cobras cause other detectors to false!). Instead it analyzes the signal over the course of several sweeps. This way other signals won't be missed while it's locked on to a specific signal. Since a RD doesn't need to extract any information from the radar signal other than the existence, frequency and strength of it, unlike a scanner which has to pull audio from the signal, there's no need to "park" on a specific frequency.

Some detectors such as the Bel RX65 have a "Ka USA" mode where it only scans the frequency ranges used by radar guns in the USA. This speeds up the sweep and increases sensitivity on Ka. The Bel STi-R takes this a step further: it lets you selectively enable and disable frequency ranges within the Ka band.

4. ## Re: In Nitty-Gritty Detail, How Do Radar Detectors Work?

^^^That's an excellent, yet simple explanation.

5. ## Re: In Nitty-Gritty Detail, How Do Radar Detectors Work?

Take a look at some patents. They may not necessarily tell you exactly how the units work, but they'll give you a very good idea of the concepts involved. That will be about as nitty-gritty as you can get, without working for a detector company or opening up a detector on the bench and probing around yourself.

(BTW: V1 "parks" too )

6. ## Re: In Nitty-Gritty Detail, How Do Radar Detectors Work?

Originally Posted by djrams80
^^^That's an excellent, yet simple explanation.

x2, nice job. Tough to explain VCOs, varactor tuning and frequency synthesizers.

7. ## Re: In Nitty-Gritty Detail, How Do Radar Detectors Work?

Thank you, that is a great explanation!

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