Remote Start

[Old Ray]

If enough people share that opinion maybe Ram can be persuaded. .

....really ................ could you get them to throw in a tow mirror fix that we could buy as well ?
You know the old story about hitting a mule on the head is not to teach it anything, its to get its attention.
FCA has a sore head, ......... but they are not listening !

 

[Electrical]

I’m not an RF engineer, so my understanding may be limited; however, I was under the impression that a small antenna outputting a weak signal (key fob) can be received by a large antenna (vehicle) but that same signal cannot be broadcast from the large antenna and recurved by the small one unless the strength is boosted (which the fcc prevents) or the small antenna is increased in size.

Obviously, this can be done at a small size since many other manufacturers and aftermarket remote starters are 2-way; I don’t know what the size of the current antenna is in the fob, but based on needing a second antenna for low frequency and all the extra electronics there may not be enough space for a high frequency antenna large enough to receive the FCC restricted signal strength from the truck at long range.

I wonder if semantics is muddying the waters. Forgive me if you know this but "large" and "small" in electrical speak doesn't typically refer to absolute physical dimensions but instead refers to physical dimensions relative to a wavelength. To further confuse things, in the RF world those terms can refer to antenna gain.

Here's a chip antenna that lends itself for use in compact electronics like a key fob or TPMS sensor, no larger than 0.5" on a side. A quarter wavelength at 433 MHz is 6.87" in air. So, a disconnect exists and performance compromises were made in favor of small size. One of those compromises must be reduced antenna gain; such an antenna has a reduced ability to detect 433 MHz in the air and when it does, the recovered amplitude is smaller than would be on a "properly" sized antenna. The 2nd antenna below, however, may have a conductor sized perfectly for 433 MHz and will have many fewer performance compromises.

Both antennae will transmit and receive 433 MHz, over a range of various power levels, but the "efficiency" at which they do so is the only difference. Both can be driven to stay within FCC approved power levels with no problem. All of these discussion points can be repeated for the LF 125 kHz antenna.

The 3rd pic below is the chip I used for TPMS. A key fob chip would be similar but without the analog pressure and temperature sensors. As you can see on the radio transmitter block, this chip is TX only (transmit). A two-way fob just needs a "fancier" chip that has both TX and RX here. After receiving a START confirmation from the truck, it'd simply drive one of the general purpose IO's to feed an LED.

Two-way would be very simple to do... and now that I think about it more, I wish it was there too!


Linx Technologies p/n ANT-433-USP


Linx Technologies p/n ANT-433-PW-RA


Freescale p/n FXTH87

 

[Electrical]

I guess if done smartly, it wouldn't have to take much away from the battery life. Maybe just a double or triple confirmation blink would be enough... without the need to drive the LED constantly.

 

[Chris]

Gain is what I was referring to, not the frequency it is tuned to receive. The last time I really messed around with antennas was when the OTA television broadcasts first switched to digital; a "small" antenna with limited gain and a built in amplifier could assist in providing the gain and signal reception of a larger antenna to a point; however, that only worked to a degree, and eventually the amount of amplified gain just led to noise making the digital signal unrecognizable, regardless of the efficiency.

I wonder how much extra gain you can get out of that tiny amplified antennas reception before the noise becomes too great and the only way to improve the range becomes an increased physical size to increase gain without amplifying noise; maybe this correlation is flawed, and the new antennas and/or simple remote commands are much less susceptible to such noise.

 

[Electrical]

You got it, Chris. Idk the limits of that little chip antenna but I tested it at about 25 ft through two walls and it did fine. That FXTH87 is programmable to about 10 different transmit power levels; I was using one of the lowest ones to see how weak I could go but still communicate reliably. I'd guess that with line-of-sight and a higher power level, that thing could probably do a few hundred feet.

I think one of the main things that helps small compromised antenna like this are advances in signal recovery circuitry. Idk what magic is going on, but good chips today can recover signals that are as much as -90 dB down... that's about 30,000 times smaller amplitude than what was transmitted!

 

[Jackham]

Well for the what it is worth category here goes. At the moment as my truck is in JB I am still driving my 2011 ecoboost Supercab XLT Ford. I was advised when ordering it by the dealership to not order the remote start but rather get it from Ford after it arrived. By 2011 Ford had made this a simple plug and play under the dash. The reason? The factory system is under Fed Law to limit its reach, but after market systems are not under such restrictions and my FOB is living proof...it reaches clear through large hospitals and across very large parking lots and not line of sight.

Also the Fob beeps twice and flashes green under the buttons when the Ford starts. If it fails to start it flashes red twice at the top.

So this is interesting theory in this thread, but has anyone actually asked a RAM engineer. Might be the easiest.

 

[Neurobit]

I noticed this morning that when I started the truck, via push button on the dash, that the LED one the fob turned red briefly, so they are indeed 2-way. First time I noticed this since I happened to have the FOB in my hand instead of being in my pocket.

 

[Brent T]

I noticed this morning that when I started the truck, via push button on the dash, that the LED one the fob turned red briefly, so they are indeed 2-way. First time I noticed this since I happened to have the FOB in my hand instead of being in my pocket.

I will watch for that also. Wonder why the hell it flash when you use remote to start it ????

 

[Chris]

Low frequency has to be two way; it responds when you grab the truck door handle or press the ignition button. If it didn’t respond, truck doesn’t start or unlock.

However, that doesn’t mean the high frequency has the same two way functionality.

 

[Electrical]

It'd be a miss from Ram if the RF was two-way and they didn't tout that. I mean it sounds like a lot of people want it and it'd look good on a feature sheet.

 

[Neurobit]

Being a proximity key, i just assumed it was 2 way, since not only can you command from the fob, but being in the proximity/geofenced area of the handle, the receiver knows it before you touch anything.

Not only that, receiver knows the fob is outside the cab without any manual command from the key.

Im not an RF expert, but that seemed like some two way talking to me.

Yup. My thoughts exactly.

 

[Neurobit]

You know what, i am rethinking what I said...

A piece of me consoders it can still be 1 way.. when I put it in terms of a transmitter and a receiver: in order for 2 way, each side needs to be a receiver, right?

I think there could be only 1 receiver, in the truck. When you use any command of the Fob, trucks receives and delivers your command.

Same I suppose could be said for the geofence and handle. The 1 receiver in the truck is simply receiving signal that the transmitting Fob is within a range, a specofoed range for unlockong doors, as well as a specofied range for when doors are closed and a Fob is too far away, as well as a low battery. I assume a weak transmitting signal is what triggers tge dash to say Fob energy is low.

So, i think i am concluding with...1 way.

Right, but if it was one way, the LED wouldn’t flash when you unlock via the handle, or start the engine w/ the dash’s button, so it does receive the signal from the truck when these take place, so pretty certain it’s two-way, otherwise that would not be possible.