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Radio Direction Finding Forum - Discussions regarding direction finding and transmitter location

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Old 05-01-2016, 9:44 PM
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Yeah that's it. It was the PopSci article I was thinking of, no wonder I couldn't find it on Youtube LOL! I hadn't seen that video you linked to.
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Old 05-01-2016, 9:44 PM
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How do they keep the two newer ones from interfering with each other?
Not had any issues

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Old 05-01-2016, 9:47 PM
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Originally Posted by Voyager View Post
How do they keep the two newer ones from interfering with each other?

Do they respond to different frequencies?
RFID readers can process multiple responses at once. The readers will "see" tags from other systems, but the computer that processes the toll simply ignores reads from tags on other systems. If I had to guess there is a "system identifier" at the beginning of the data burst that tells it what system it belongs to. I have an EZ-Pass and a K-Tag on my windshield and neither have any issues going through the other's tolls..

Last edited by KD0TAZ; 05-01-2016 at 9:59 PM..
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Old 05-01-2016, 10:45 PM
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I was thinking maybe they responded (were powered) by different frequencies. If they were on the same frequency, I would think they would respond at the same time unless there were a capacitor that was different that resulted in different charge (hence response) times.
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Old 05-01-2016, 11:41 PM
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The tag, after being woken up, is flooded with a CW carrier that powers the electronics, charging a capacitor. The tag then modulates its antenna with a transistor switch, on and off, which creates sideband energy. This energy is radiated back to the reader as "backscatter". The homodyne receiver extracts the data.
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Old 05-02-2016, 1:15 AM
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Quote:
Originally Posted by Voyager View Post
I was thinking maybe they responded (were powered) by different frequencies. If they were on the same frequency, I would think they would respond at the same time unless there were a capacitor that was different that resulted in different charge (hence response) times.
They will respond simultaneously. It's the job of the computer system that the readers dump their data into to sort out which tags belong to the system and which ones do not. Even the "semi-active" tags that EZ-Pass uses will respond - because systems that use the passive sticker tags also use semi-active tags for big rigs, motorcycles, and other vehicles that can not use a sticker tag for some reason (GM's metallic coated windshields for example). Semi-active tags are basically active tags that do not continuously transmit their ID. They sit in sleep mode until the signal from the reader (the same signal that charges the passive tags) wakes them up, then they broadcast and go back to sleep. This allows the internal battery to last many years.

Last edited by KD0TAZ; 05-02-2016 at 1:24 AM..
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Old 05-02-2016, 11:53 AM
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OK. So the only answer is that "the computer has to figure it out", and they do in fact interfere with each other? Maybe the energy is at different levels even if the two units are right next to each other, and that is how the distinction is made?
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Old 05-04-2016, 1:32 AM
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Well, seeing you are in Florida, those roads could be toll roads already... you and the other commuters just don't know it yet. It's hard to keep up with communicating when you have so many miles of toll roads to accumulate. We have to keep adding toll road miles, someone might beat us for #1!!!

But in all seriousness, I hope the OP will filed a Freedom of Information Act request with the state highway department for the locations and uses of all RFID tag readers on the state's roads. Counting cars is one thing, but their are cheaper and less invasive methods to do that. Using the RFIDs is without a doubt "research" tracking an individual and his habits. I bet none of the subjects consented to the studies... I am more than happy to help you research this information.

Regarding the toll road booth speeds, here in Texas, I roll through our toll booths going 85 mph -- and that's when I'm following the posted legal speed limit. One thing they've done right is designing them without the traffic hazards of manned toll booths (and without having to place people in the middle of the road).

My state has 30-50 billion dollars in liabilities for toll roads currently. It's awesome.
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Old 05-04-2016, 6:48 AM
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Originally Posted by dave3825 View Post
On Long Island, they scan ez passes to give an eta to a major road.
RFID Provides ETAs to N.Y. Drivers.
That's in more than just Long Island, and it's been going on for at least two decades that I know of.
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Old 05-14-2016, 8:09 PM
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Quote:
Originally Posted by AggieCon View Post

Regarding the toll road booth speeds, here in Texas, I roll through our toll booths going 85 mph -- and that's when I'm following the posted legal speed limit. One thing they've done right is designing them without the traffic hazards of manned toll booths (and without having to place people in the middle of the road).

My state has 30-50 billion dollars in liabilities for toll roads currently. It's awesome.
Must be talking about the 130 road near Austin. Nice road and it saves a lot of time not sitting in Austin during rush hour traffic.
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Old 05-14-2016, 8:27 PM
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Must be talking about the 130 road near Austin. Nice road and it saves a lot of time not sitting in Austin during rush hour traffic.
Talking about 130 in the middle of Caldwell county. It's a joke! For the longest time the state tried to keep traffic numbers form the San Antonio Express News. I'm not sure if they ever even released it. I love how TxDOT allowed them to modify the ramp and signage to fool people into staying on the road instead of taking the Toll 45 spur back to I35 to get to San Antonio. Not to mention to speed limit drama regarding 183 (they wanted to force people to take a toll road that was built next to an existing highway). Fast, empty road, but I doubt it's very useful for many folks.

Would not a more prudent approach would have been a Jersey Turnpike type approach on the corridor that is actually busy? Now we have a road hardly anyone uses, an existing road that is still a mess, and billions with a b more debt to show for it.

Wow, you hit one of my buttons there.
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Old 05-15-2016, 5:11 AM
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Default Florida's "iFlorida" project for using toll tags on traffic monitoring

Just came across this thread. FDOT and FHWA did sponsor a project in the early 2000s that used SunPass receivers at locations both on and away from the tollways to help determine travel times along arterial corridors. They were just for creating probe vehicles and not used for enforcement. Essentially, its the same thing that Bluetooth based systems are using today. Here's a link to the research report:

http://ops.fhwa.dot.gov/publications...0/iflorida.pdf
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