Radar information Pages


CMI Incorporated Speedgun & Magnum X band

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There are many generations of the Speedgun.

Both Moving and Stationary.  X band radar 10.525 Ghz

This gun has a single display.  Moving versions have two displays side by side.

The Magnum has moving capabilities and is a different color shell.

Each toggle switch on the Magnum has three position toggle switches, the Speedguns have two positions.

How it works

Example start up for the testing shown here:

Plug unit in to cigarette lighter or regulated power supply 12 volts.

Flip Top switch to Stationary (STA.)

Power up: (Flip bottom switch left), squeeze trigger, unit in Standby mode

If you did it quickly enough "00" is displayed otherwise screen is blank.


When screen is blank and no dash on left, unit is transmitting X band radar.

To take a reading:

Point unit out window (to minimize strong return reflections) squeeze trigger.

This Speedgun trigger is like an on / off button.  Very simple operation.

  Squeeze trigger, transmit radar, squeeze trigger to lock in reading and stop transmitting.

( To check the calibration of the unit we strike* a X band tuning

fork which produces a 60 MPH reading in front of the antenna. )

Strike* tuning fork and obtain a 60 MPH reading....

This should be done each shift / day if not at each reading.

Each state has rules about the length of time between certifications.  6 mo./1 yr

If you get nothing its because the unit locked (dash) in the last reading. 

Squeeze trigger and let go.

The Magnum, since its moving mode capable, needs two tuning forks for patrol and target readings.

There is a SPECIFIC order spelled out in the operators manual.

Copies below.

Just hanging two tuning forks in front of the unit WON'T get the right result, see below:

Above the 65 and 30 MPH tuning forks should yield 65 patrol and 35 target.

While the target reading is spot on in this example, the patrol speed (moving) isn't accurate.

No way is this tuning fork test being done one handed......

Field Report.

There is no LED segment display check function so this is as close as you get.

This is the first display at power up.

After using a tuning fork to check the unit, next

 test the internal calibration function flip top switch to the left (Cal)

to get a reading of 30 MPH

Unit is ready for readings / clocking / speed monitoring.

Point head-on (parallel) to oncoming traffic or in direction of car travel.

Here are two reflection readings from driving down the interstate


(these are MPH K15-II used for illustration)

These show "Our" speed from the reflection of the signal off trees and signs.

This 149 MPH reading was tuning fork induced by a K band fork.

SAME reading displayed below on the Magnum:

The right red X is the locked reading, the Speedguns do this with a dash on the left.

The Left red X means over 100 OR RFI interference during a reading.....

This unit can get feedback from the Doppler Audio which will get readings around 29 - 31 MPH.

To turn down the Audio use this knob.

This unit will clock from about ~9 MPH to well above 150/180 MPH

This the front of the unit as point at the object to be clocked.

Notice the sights on the top.  It is a good attempt to help aim the units radar beam.

However, the beam spreads out so fast (beam width) that it can be 300 feet wide.

You can notice the angle from this picture of the cone.

This unit can be sensitive to small reflective targets like a golf ball up to ~50 yards.

FYI: Basketball free throws average 11 MPH.

Some radar web site(s) will recommend this for baseball, softball and small targets.

It will display ONE reading at a time and the sample rate is quite slow.

Once you lock in a reading with the trigger, you can't read anymore speeds.

Cross Readings or Interference:

High power radios, transmitters, power lines are all documented sources of interference.

Both the X band 10.525 Ghz and the K band 24.150 Ghz frequencies are so close,

I always suspected interference or the ability to receive another's signal as a speed reading.

So I tested them against each other at about 120 feet.  This CMI Speedgun seems

to be sensitive to the Doppler audio when another K band unit is transmitting nearby.

The CMI X band unit in a test, read 95 when testing by a radar detector.

There was a K band MPH K 15 -2, approximately 2 feet away transmitting.

While the other gun wouldn't register a speed from the CMI Speedgun,

the Speedgun would register 29,30,31 or 32 MPH when picking up the K band transmission.

Tuning Forks.

I cross referenced these four forks:

65 MPH K - gives ~149 MPH on the X band gun

65 MPH X - gives ~28 MPH on the K band gun

60 MPH X - gives ~26 MPH on the K band gun

30 MPH X - give ~13/14 MPH on the K band gun

This table means each X and K frequency band will overlap into the other

in determining the speed of a target.  Direction of the target (towards or away from) will

determine if there is a frequency overlap or not.

Glossary & Reference:

Strike * :  Some manufacturers claim to strike the metallic tuning fork on a non-metallic surface to produce an accurate tone.

Striking a tuning fork on a metal surface can dent the fork, damage it, or create false

overtones which will affect readings obtained by the unit.

Sample rate:  is how often a new reading is taken and displayed.

Below are older versions of the Speedgun.


Speedgun 8 (left)  Speedgun Magnum moving version (right)

CMI Speedgun / Magnum Operators manual