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TPMS Pressure Canister Antenna

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Gersh42

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Hello I am brand new to the form and please excuse my ignorance, but I know very very little on this topic.

I have a 2007 Corvette with a tire pressure monitoring system, the frequency of the sensors are 315 MHz. I have installed a set of drag racing wheels and tires that are not compatible with the factory sensors. Unfortunately, the ECU needs to see a safe tire pressure to keep the traction control from coming on.

My solution was to machine a pressure canister that would house all for TPMS sensors and trick the computer (it’s been done plenty times before by others) my fatal design flaw is I made my canister out of 6061 aluminum and that is blocking the signal. Currently, I made a temporary canister out of ABS and everything is working and the car is “happy”. I would prefer to use the nice aluminum version, I went to a lot of trouble and expense.

Is there any way that antenna could be added in order to allow the radio frequency to pass by the aluminum canister walls?

Thank you for any help
 

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You need two antennas and a short connecting wire. Place one antenna inside the can and one outside it with the cable passing through a hole. Obviously, make the cable and hole airtight! If you can use 'semi-rigid' co-ax cable all the better because it is mechanically strong enough to glue or cable tie to the outside of the canister and there would be no risk of air leakage through its insulation. It is expensive though.

Over very short range the antennas will couple signal to each other and it should allow enough to escape to reach the receiver.

Brian.
 

So if I understand you correctly, if I purchase a semi rigid coax cable like the ones below and have an antenna on the inside and one on the outside would it be able to read the frequency from all four sensors on the same antenna?

Also, any idea what is inside of the coax cable? Looks like the outer shell or body is made from steel, wondering if it could take any heat from Welding a fitting to it… but I think I already know the answer to that hah

Thanks for your help
 

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Basically yes, an antenna converts electromagnetic waves (radio waves) into a voltage when receiving but it also works in reverse, applying a voltage makes then create electromagnetic waves. If you connect two antennas back to back, excepting that there will be some signal loss because they are not 100% efficient, the signal gets coupled from one to the other. The one inside the can picks up the TPMS signal and the one outside radiates to to the ECU's receiver.

Coax is a shortened name from "concentric-axial", meaning "in line with one inside the other". It is a kind of cable with an inner wire suspended centrally in some insulation and inside an outer screen sheath. I suggest semi-rigid cable because the insulation is normally solid but flexible plastic so it is air tight. Electrically, the coax cable used for example on TV antennas would work equally well but it usually has a cellular construction which would allow air to escape. That would make it difficult to pressurize the canister. You can solder to the outside of semi-rigid coax but you can't easily solder to aluminum so I would recommend forming it to shape then using epoxy resin to seal the hole.

There is an entirely different approach to this problem which you should consider but it takes some programming skill: The TPMS units as basically a timer that wakes them up every few minutes, a pressure sensor and a low power radio transmitter. You can make a small unit that mimics the TPMS signals and fools the ECU into thinking it sees real data. You only need one unit, it can mimic all the TPMS senders by sending fake information in sequence. I haven't done this myself but it isn't technically difficult, I can read my own cars TPMS on a radio receiver here (we use 433.92MHz in Europe) and it is just a stream of numbers, if I copied good data and kept resending it the ECU would be none the wiser, even if the wheels were completely removed! I'm thinking of something small enough to fit inside a tiny box or a USB stick enclosure.

Brian.
 

I appreciate all of the great information! The second option is definitely intriguing but at the moment is beyond my skill set.

After searching for semi rigid, coax cable, I discovered this hermetic sealed SMA to SMA bulkhead connector. Also ordered two SMA antennas along with it. It sounds like it will be perfect for my application, as it is designed to hold pressure or vacuum. I had a small drain valve at the bottom of the can that I can now replace with this fitting. Thank you very much for your help I feel confident now that this will solve my problem.
 

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