1. ## Question: Spec mode and police radar

Ok, I know that the Spec mode found on Belscort units can be off a little, but lets say you were to detect a LEO running 34.9XX,instead of 34.700. Or 35.3XX, instead of 35.500. Or also when a V1 can't detect a Multanova when on Euro because it has fallen "out of tune."

Does this mean that the speed reading that the LEO/camera is getting could be wrong?

2. ## Re: Question: Spec mode and police radar

Originally Posted by ELVATO
Ok, I know that the Spec mode found on Belscort units can be off a little, but lets say you were to detect a LEO running 34.9XX,instead of 34.700. Or 35.3XX, instead of 35.500. Or also when a V1 can't detect a Multanova when on Euro because it has fallen "out of tune."

Does this mean that the speed reading that the LEO/camera is getting could be wrong?
The speed reading could be wrong, but usually only slightly, unless there is a BIG difference in frequency.

For example, with a difference of 200 MHz: the doppler shift for 1 MPH @ 34.7 GHz is about 103.51 Hz, while the doppler shift for 1 MPH @ 34.9 GHz is about 104.11 Hz, so a difference of .6 Hz. So if the target vehicle is travelling at 100 MPH, and the radar signal is at 34.9 GHz while it is supposed to be at 34.7 GHz, this would result in doppler signal which is 60 Hz too high. Although 60 Hz isn't quite 1 MPH (103.51 Hz would be per above), maybe the counter circuitry would add 1 MPH to the target speed if it is rounding or something ( I dont know if it does this or not).

If the target vehicle was travelling at 200 MPH, the radar unit would certainly add 1 MPH to your speed, since at 200 MPH the doppler shift would be 120 Hz high (which is more than the 103.51 Hz for 1 MPH)

Hypothetically speaking: at the extreme, if a radar unit was supposed to operate at 33.4 GHz and it somehow drifted all the way to 36 GHz, if the target vehicle was travelling at 100 MPH it would add about 8 MPH to the target speed and display 108 MPH.

Jim

3. Doesn't that assume the shift is measured from what the freq is supposed to be, versus measured from the actual transmitted signal?

Which way does the radar work? (spec or actual tx)

4. I think I see what you are asking...
Basiacally what happens, is the transmit/receive is generally in one assembly. A portion of the transmitted signal is mixed with the received (reflected) signals, resulting in the difference between the two. This difference is what is sent to the "counter circuit", which is all the counter circuit sees.

As far as I know, no current models of police radar change the way the counter circuit calculates speed based on the actual transmit frequency. The radar unit doesn't even "know" what actual frequency it is transmitting, it is set to calculate speed based on the spec'd operating frequency for that unit.

5. Jim, I think you understood me too.

So if a radar's transmitter was out of spec and transmitting off freq by a little, since the radar return is compared to the outgoing radar signal, and the difference is calculated and turned into a speed reading, the speed reading should still be correct.

A RD users ability to pickup the signal could be affected if the transmitter was far enough off frequency.

Also I think what you said can also mean that a user's RD in spec mode isn't going to show a shift in the speed due to their own vehicle's closing rate on the radar, since the shift is so small.

6. Ah, I see Thanks Jim

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