V1 Rear Antenna

[radarTom]

Today as I was driving, I came up behind one of those "Your Speed Is:" signs from the back. My V1 gave me fairly OK warning that I was coming towards it. On my way back, the V1 alerted me appropriately as I was now heading straight towards the front of the sign. After I passed it though, the alert quickly died out. No real arrows pointing backwards.

It seems, then, that the front antenna is much more sensitive, I'd guess because of size, than the rear. The front did pick up the weak signal from the rear of the sign, whereas the back antenna really couldn't.

Does this have some implications about how to interpret rear alerts? When you're getting a rear signal, it must be fairly strong if it's lighting up the rear arrow. Right?

[DogGod]

In my 1.7 it seemed like the rear antenna was better, I havent had much time to test out my 3.851 yet. It may be my tint strip but I dont think that it is metallic. From common sense it would seem like the front one is stronger. I wish I had a radar gun.

[jimbonzzz]

Yeah, the rear antenna definitely has less gain than the front antenna, other than that, the circuit for the front and rear are identical. So this could certainly be what you are seeing.

But also keep in mind that when the speed sign's antenna isn't aimed directly at one of V1's antennas, the only thing there is to detect is radar reflections from other objects, terrain, etc. So if there were other vehicles for the radar to reflect off of, your encounters can vary quite a bit...

[GTO_04]

I find the rear antenna to be just as sensitive as the front antenna. MIke V told me in an email that, at least on Ka band, that the rear antenna should have just about the same range as the front antenna. X band is probably a different story with the lower frequency. The difference in horn size may play a bigger factor there.

Just this morning, I got one mile range on the rear antenna on 35.5 GHz. Pretty good IMHO given that there were some hills on that road.

GTO_04

[radarTom]

I don't recall what band the sign was running on. I'll have to take another drive-by.

[Switchback]

another issue is to consider is f there were any vehicles behind you for the radar signals to reflect from.

ideally if there was nothing to reflect the signal back towards your car. the signal would not be detected. the antenna on that speed sign points the radiation in 1 general area. it is not like a television or radio braodcasting antenna which is designed to radiate in 360 degrees. Think of the emissions from that radar antenna as a cone-shaped signal with the small end at the sign and the larger side out in the direction the sign is facing.

[LS2]

All I can say is from the rear it picks them up way way back there. It is sufficient.