January, 2017

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K-band Filtering

Written by infiniti

What it is and why you need it to find real K-band threats

Objective: to inform the public about the sources of K-band pollution & false alerts, how detectors go about reducing them, and what those detectors give up in terms of potential real K-band misses. This will help consumers make a more informed purchase.


The K band is a section of the radio spectrum with frequencies between 18 and 27 gigahertz (GHz). This band is a very popular band used to detect motion in a variety of applications, including: automatic door openers at shopping centers, speed cameras, traffic sensing radar, construction signs, and speed signs. All of these sources are in fixed locations and, in practice, we have been able to block out alerts from these safe K-band sources using GPS-based location lockouts. More recently, however, manufacturers have also begun using K-band radar-based safety systems in newer cars and big rigs. These include in-vehicle safety systems such as blind spot monitoring (BSM), and collision avoidance systems (CAS), both of which can cause K-band false alerts by radar detectors. These new applications for K-band radar are moving sources, and thus cannot be locked out as we have been doing with location-based lockouts. They must be filtered out by other methods.

While the Ka band (26.5-40GHz) has some sources of falses also, we have been able to reduce those by dealing with certain sections (or segments) of the Ka radio spectrum frequencies. Specifically, we turn on only those segments where known Ka guns are tuned to operate, including: 33.8 GHz, 34.7 GHz, and 35.5 GHz. We can essentially ignore segments of the Ka spectrum that do not contain legitimate sources of police-operated Ka radar and only listen to those areas where police radar exist.

Unfortunately, the K-band spectrum cannot be effectively segmented as the K-band police radar guns and all of these other sources use many overlapping frequencies. Without the ability to filter out K-band false alerts by segmenting the K-band, we are left with a nagging radar detector that is sometimes called a “new car detector” since it will let you know, among other things, where every BSM and CAS system is on the road around you.

The growing number of K-band sources creates a near constant barrage of audio and visual alerts that can lead to two issues: (1) spending too much time trying to locate real K-band sources or, even worse, (2) completely tuning out K-band alerts, including real K-band police radar tracking your speed.

For more information, see:

So, how can we quiet down a detector?

There are many current approaches radar detector manufacturers are using to help quiet down detectors and reduce the number of false alerts. There are many benefits and also risks associated with each approach. So, don’t automatically think that a quiet detector is a better detector. Some of the quietest detectors on K-band are actually some of the cheapest detectors that have terrible K-band range, so they aren’t sensitive enough to pick up radar signals in time to warn you of real police radar until you are at or near the kill zone (the area in which police can actually determine your car’s speed). Others have been shown to accidently automatically lockout real police radar. It’s important to understand the mechanisms manufacturers are using and to select and use a detector based on that understanding.

K-band false alert reduction techniques

  • Location (GPS) based lockouts for stationary K-band sources – allows users to manually or even automatically lockout K-band signals based on their location. This is very helpful for known stationary K-band false sources such as automatic door openers in shopping centers, construction signs, and speed signs. When you are alerted to K-band and determine the source is one of these known fixed K-band sources, you can manually prevent that frequency signal from alerting you in the same spot in the future (aka locking it out). Some detectors also have the ability to automatically learn and lock out those signals after repeatedly seeing them several times.

    It is important to note that location-based lockouts are handled differently by each detector – some still give full visual warning with reduced volume, some give a grayed out visual warning and no audio. Also, some detectors (like the Valentine One) require a Bluetooth (BT) module and a smartphone with GPS location enabled to be paired with the V1 in order to lock out location-based stationary false alerts. Be sure to check the lockout display options as you do your research to find the detector best suited for you.

  • Low-speed muting – blocks all sources from alerting audibly, visually, or both when traveling under a user-selected speed. This allows users to quiet down both stationary and moving sources of K-band when traveling around town at low speeds such as when in stop-and-go traffic or when sitting at a red light. Low-speed muting is not determining whether a K-band source is safe or a real police K-band source, but if you set your speed threshold at an appropriate level, it really won’t matter either way. This is very useful when you are in and out of parking lots of shopping centers, in heavy traffic, and so on.

  • Reduced sensitivity (manual) – allows users to manually reduce the sensitivity or range at which a detector will notify you of a K-band signal. For example, a detector may have an auto mode or a “city” mode that will only alert you to a K-band signal that is over a certain signal strength. This is handy for filtering out weak automatic door openers on the side of the road, for example. So, in practice, if highway mode will alert you of everything it “hears” then auto or city will only alert you if it is strong enough to be a serious threat. If you think of signal strength as a percent, highway mode may pick up signal strengths of even just a few percent while city mode may only pick up signals strengths above 40% or 60%. This is great to quiet down a detector, but it typically will also have a proportional reduction in the range of K-band alerts for real police K-band radar.

  • Speed-based sensitivity (auto) – like Reduced sensitivity above, speed-based sensitivity reduces the sensitivity or range of a detector based on the speed you are driving. This “Auto” mode operates similar to how automatic volume control can work on certain cars – the faster you go, the louder the stereo becomes. Likewise, the faster you go, the more sensitive the K-band settings become. There is often a speed (say 45MPH) at which it will be set at maximum sensitivity since it will assume you are traveling at a highway speed. This way you don’t have to manually switch between sensitivity levels while driving and the detector can take care of things for you.

  • Filtering – reduces K-band falses by blocking out known types of false sources or by only letting in known real police sources of K-band radar. Radar signals can be identified in several ways: This is done by taking a deeper look at the underlying properties of the transmitted signal itself beyond just the basics like frequency or signal strength. Some modern detectors can do more advanced signal analysis to analyze modulation patterns and other attributes of the signal to identify its “fingerprint” to recognize, for example, the difference between a continuous wave police radar gun and a frequency modulated blind spot monitoring system.

    This type of filtering provides an ideal solution to the issue of false alerts, assuming it is programmed correctly and up-to-date. For example, if a detector is built to ignore all k-band sources except for legitimate sources, then it must kept up-to-date as new blind spot monitoring systems are released.

  • Delaying – reduces K-band falses by eliminating signals of short duration. This is very helpful in cities that use traffic-sensing radar. Traffic sensing radar sends out short bursts of K-band radar on a regular basis (say, half second signal every 60 seconds). By enabling a delay, many detectors can completely eliminate alerts from these false sources of K-band. The risk of using a delay to quiet down falses is that some police radar can be used in instant-on (I/O) mode, that can capture your speed within a fraction of a second and if the shot is too short, your detector may filter it out. While many police use constant-on (C/O) radar, there can be an impact here as well. When picking up a weak signal at a distance, the signal may come and go and your detector is trying to see through trees and beyond traffic ahead. If the signal isn’t able to be “seen” for a long enough period of time, your detector may not alert until you get closer and the signal is able to be picked up for a continuous period of time.

Let’s take a look at some of the most popular windshield mount detectors and how they each allow you to reduce K-band false alerts.

How manufacturers reduce K-band false alerts in popular windshield-mount detectors

What about remote-mount detectors?

For comparison purposes, there are remote installed detectors that are comparable to many of these windshield mount detectors. While not identical, the following detectors will be similar in K-band performance and quietness due to shared platforms and/or components:

Impact of K-band false alert reduction techniques on range or sensitivity

Since many of the detectors use several different mechanisms to quiet down K-band, you should be wondering: How will this impact K-band range for real police radar? Great question. Let’s take a look at some testing from the members of the RDForum:

Testing how Auto Mode & TSR reduce range


TXCTG – Waco Pioneer Pkwy 35.5, 34.7 and K-band Testing 7-31-2016


As the progression of K-band filtering has really picked up with new platforms like the Radenso XP, Net Radar, and others, it will be important to continue to test these new filters in a variety of real world scenarios to assess the impact on delaying or missing real alerts.

Detectors with a good balance of quietness and good K-band range

Given the benefits and risks associated with different K-band quieting techniques, let’s look at a few windshield mount detectors that seem to have a good balance of K-band range with a quiet ride.

  1. Radenso XP


  2. Uniden DFR7


  3. Valentine One (latest version with TMF2)


  4. Max 360


Running a dual-detector setup

Given the trade-offs associated with K-band filtering, there are some RDForum members who enjoy running two detectors – one quiet on K-band (typically from the list above) paired with a long range Ka band detector, like an Escort Redline windshield mount or a 9500ci remote mount detector with K-band turned off.

While some worry about interference, most agree that with about 3 ft of separation between windshield mount units and a preference given to running one windshield and one remote mount, it can still deliver reliable results. In particular, most members who have run a dual setup for years and are highly satisfied, run a V1 on the windshield paired with either the Redline on the opposite side of the windshield or a 9500ci, STiR-O, or STiR Plus remote unit.

While this significantly adds to the total cost of a radar detection system, many enthusiasts want the best of both worlds – a quiet K experience and the fantastic Ka range. Others have the complementary setup – a quiet K-band remote and a long range windshield detector. In this case, many have run the ALP Net Radar remote unit for a quiet K-band experience along with a Redline or Magnum windshield mount for extreme Ka range.


K-band sources are on the rise. With many of the in-vehicle technology systems filtering down to less expensive vehicles, there will soon be K-band signals from most of the cars we encounter – especially in major cities. The proliferation of moving K-band falses, along with existing stationary falses can create a situation where we miss or fail to pay attention to real police K-band signals until it is too late. While many manufacturers are using a variety of techniques to address these issues, it’s important to understand which techniques your detector has and how best to use them to quiet down your ride while maintaining a reasonable alert distance to give you time to react to real threats. In addition, it will be important to continue to test the filtering each manufacturer is using to ensure we are balancing quietness with the range and situational awareness we expect from a quality radar detector.


This article would not have been possible without the support of the active members involved in the RDForum.org groups. The fantastic looking visuals were created by erickonphoenix. Many thanks erickonphoenix for helping to create very clear illustrations to help the readers quickly pick up the key concepts. Brainstorm69 and Vortex, thank you for your comments and suggestions to help build out the article. I also appreciate those who completed tests that we've referenced in the document, especially the TXCTG group. Without the testing and sharing of unbiased results, this forum would probably cease to exist. We welcome your comments on the article and will make revisions as needed.

Thanks to infiniti for writing this article.