# Thread: What determines the frequency ?

1. ## What determines the frequency ?

What kind of signal do radar guns emit, is it coded ? Does the frequency change after each use ? How accurate is the internal filter ??

2. ## Re: What determines the frequency ?

Originally Posted by Force5
What kind of signal do radar guns emit, is it coded ? Does the frequency change after each use ? How accurate is the internal filter ??
No, it isn't coded. The signal is "unmodulated continuous wave".
The frequency doesn't chance after each use, excep for how it normally chanes as a result of time, temperature, etc.

Jim

3. But didn't some people here encounter a situation where more than one radar gun is used ? Now if they operate on the same frequency, how can they distinguish which signal is being returned to the gun ?

How would each gun recognize it's own return if all of those guns were operating at 24.150?

5. Originally Posted by TexasRed

How would each gun recognize it's own return if all of those guns were operating at 24.150?
Very interesting... and if it is far away, even laser would have this problem?!

6. There is a slight diff in the freq it transmits. for exampe if u have 2 kr10sp units trans kband at 24.150 ghz. if u get into the techs of the freq it is like 24.150.000.007 ghz and the other gun is 24.150.000.020 ghz. your radar det will pick both up beacuse they are both 24.150 but each individual unit knows what was trans and what was recieved. i sit in the uturn talking to other troopers and we can both trans ka stalker 34.7 ghz radar and pick up the same speed of a car.

7. FOCCO is right, it would be very difficult for two radar guns to interfere with each other. For example:

Consider K-Band radar. The largest possible doppler shift for that frequency is about 14 KHz, which represents the doppler shift for 199 MPH. Any frequency outside that area is ignored by the gun.

For example, for two K-Band guns to interfere with each other, they would have to be that close in frequency. So, if one gun was at exactly 24.150000 GHz, another gun would have to be at 24.150014 GHz or closer in frequency to interfere.

But in reality, two guns are almost never that close in frequency, they are generally a number of MHz different. The guns drift in frequency over time, temperature, etc. That doesn't matter for speed calculation, since the reflected doppler signal is mixed with the transmitting signal no matter what freq it is.

It is technically possible for two guns to interfere, if they happen to be that close in freq. But, it would probably be so rare that I wouldn't be surprised if there are officers who worked a lifetime on patrol and never saw it happen.

Jim

8. Interesting. Thanks professor

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