LEO StandBy mode....

[djrams80]

Cool. Then how does the radar unit know the LEO's speed when in moving mode?

I'm speaking beyond my scope of knowledge, but I believe it listens for multiple doppler shifted signals, the strongest of which is the target's speed and some other signal mixed in there represents the patrolcar's speed?

The professer is probably sleeping, but I'm sure he will have a perfect, easy to understand, amazingly informative answer to this question in the morning.

[kpatz]

I'm speaking beyond my scope of knowledge, but I believe it listens for multiple doppler shifted signals, the strongest of which is the target's speed and some other signal mixed in there represents the patrolcar's speed?

I'm not the professor, just a radar geek who knows less than him, but I'll try and answer the question the best I can until he happens to come across this thread...

Actually, I think how most guns work is they look for multiple doppler returns. The "lower" speed return is the patrol car and the "higher" speed is the target + patrol speed. The gun subtracts the patrol speed from the target speed to get the actual target speed.

Newer guns with "same-lane moving mode" use a more sophisticated algorithm, or simply reverse the roles of the two doppler signals (higher speed return = patrol, lower = target).

Some guns can be electrically connected to the patrol's speedometer, but this is just used for verification that the correct doppler return is used for the patrol speed.

As for weaker than normal alerts during traffic stops, this is caused by either (a) a handheld gun being left on and sitting on the patrol car's seat/floor, or (b) a dash-mounted gun that is no longer optimally aimed down the roadway since the patrol car moved in order to pull over its victim. Also, one may often come up to one of these cars in the same direction as the radar is aimed (e.g. forward facing antenna, coming up on rear of cruiser), so the signal will be weak and then get stronger after passing the cruiser.

Another variation on (b) is if the cruiser was parked perpendicular to traffic while clocking (with the dash-mounted antenna aimed out the side window), then the LEO pulls someone over so the cruiser is now parallel to traffic, but the antenna is now perpendicular, that can cause a weak reading until you're just passing the cruiser.

[bart99gt]

Could this be the before mentioned low power radar antenna mounted below the LEO's car that measures the LEO's vehicle speed for use with moving radar calculations?

There has never been a low power antenna used strictly for patrol speed determination.

Kustom did build one dash mount radar, the KR-11, in the late 70s to early 80s that would transmit short bursts at random intervals (1/4 - 1/2 second, per the patent I came across) while in standby/hold, moving mode only, to monitor the patrol speed of the vehicle. It would not display this speed, but rather refreshed the value in its CPU each time until the radar was turned on, at which point it would compare that value to the strongest return, which was supposed to speed the time it took for it to determine the patrol speed and consequently the speed of the approaching vehicle. This was all accomplished with one antenna with a single transmitter and receiver, despite some of the rumors/mis-information I've seen floating around this board.

I think MEM-TEK related a few months ago that these bursts were easily detected by some of the better detectors of the day. They are much, much longer than the current POP bursts.

[GTO_04]

Hand held radar gun, sitting on the seat. I've seen this happen myself.

GTO_04

[jimbonzzz]

I'm speaking beyond my scope of knowledge, but I believe it listens for multiple doppler shifted signals, the strongest of which is the target's speed and some other signal mixed in there represents the patrolcar's speed?

I'm not the professor, just a radar geek who knows less than him, but I'll try and answer the question the best I can until he happens to come across this thread...

Actually, I think how most guns work is they look for multiple doppler returns. The "lower" speed return is the patrol car and the "higher" speed is the target + patrol speed. The gun subtracts the patrol speed from the target speed to get the actual target speed.

Newer guns with "same-lane moving mode" use a more sophisticated algorithm, or simply reverse the roles of the two doppler signals (higher speed return = patrol, lower = target).

Some guns can be electrically connected to the patrol's speedometer, but this is just used for verification that the correct doppler return is used for the patrol speed.

As for weaker than normal alerts during traffic stops, this is caused by either (a) a handheld gun being left on and sitting on the patrol car's seat/floor, or (b) a dash-mounted gun that is no longer optimally aimed down the roadway since the patrol car moved in order to pull over its victim. Also, one may often come up to one of these cars in the same direction as the radar is aimed (e.g. forward facing antenna, coming up on rear of cruiser), so the signal will be weak and then get stronger after passing the cruiser.

Another variation on (b) is if the cruiser was parked perpendicular to traffic while clocking (with the dash-mounted antenna aimed out the side window), then the LEO pulls someone over so the cruiser is now parallel to traffic, but the antenna is now perpendicular, that can cause a weak reading until you're just passing the cruiser.

I couldn't have said it any better

[steve+stang2003]

Sounds like a good answer to me.
Next time it happens I'm going to take note of how the car is positioned etc and report back.
Enjoy!
Steve

[djrams80]

I'm speaking beyond my scope of knowledge, but I believe it listens for multiple doppler shifted signals, the strongest of which is the target's speed and some other signal mixed in there represents the patrolcar's speed?

I'm not the professor, just a radar geek who knows less than him, but I'll try and answer the question the best I can until he happens to come across this thread...

Actually, I think how most guns work is they look for multiple doppler returns. The "lower" speed return is the patrol car and the "higher" speed is the target + patrol speed. The gun subtracts the patrol speed from the target speed to get the actual target speed.

Newer guns with "same-lane moving mode" use a more sophisticated algorithm, or simply reverse the roles of the two doppler signals (higher speed return = patrol, lower = target).

Some guns can be electrically connected to the patrol's speedometer, but this is just used for verification that the correct doppler return is used for the patrol speed.

As for weaker than normal alerts during traffic stops, this is caused by either (a) a handheld gun being left on and sitting on the patrol car's seat/floor, or (b) a dash-mounted gun that is no longer optimally aimed down the roadway since the patrol car moved in order to pull over its victim. Also, one may often come up to one of these cars in the same direction as the radar is aimed (e.g. forward facing antenna, coming up on rear of cruiser), so the signal will be weak and then get stronger after passing the cruiser.

Another variation on (b) is if the cruiser was parked perpendicular to traffic while clocking (with the dash-mounted antenna aimed out the side window), then the LEO pulls someone over so the cruiser is now parallel to traffic, but the antenna is now perpendicular, that can cause a weak reading until you're just passing the cruiser.

I couldn't have said it any better

So, the same radar signal bounces off of fixed objects and is used to determine the LEO's moving speed and bounces off moving objects and is used to determine the target's speed? One radar source, two determined speeds? Interesting.