wr8y,
Good luck with the spectrum analyzers. A few years ago, I briefly tried using a 20GHz HP spectrum analyzer to find the frequency of a fob for a Dodge van. It didn't show up at all, which surprised me. Wasn't using any special connection to the fob; just an open-ended semi-rigid coax - but that should've picked up at least SOME kind of RF when it's actually touching the plastic fob housing.

I probably was trying to sweep too broad of a frequency range, and the analyzer was passing through the fob's frequency range between pulses - or the fob was frequency-hopping.

 

According to Maxim, the operating frequencies for remote keyless entry devices are:

An RKE system consists of an RF transmitter in the keyfob (or key) that sends a short burst of digital data to a
receiver in the vehicle, where it is decoded and made to open or close the vehicle doors or the trunk via receivercontrolled
actuators. The wireless carrier frequency, is currently 315MHz in the US/Japan and 433.92MHz (ISM
band) in Europe. In Japan the modulation is frequency-shift keying (FSK), but in most other parts of the world,
amplitude-shift keying, or ASK is used. The carrier is amplitude modulated between two levels: To save power,
the lower level is usually near zero, producing complete on-off keying (OOK).

The transmission is limited to no more than 5 seconds by the aforementioned regulation. It might actually be shorter.

John

 

wr8y,
Good luck with the spectrum analyzers. A few years ago, I briefly tried using a 20GHz HP spectrum analyzer to find the frequency of a fob for a Dodge van. It didn't show up at all, which surprised me. Wasn't using any special connection to the fob; just an open-ended semi-rigid coax - but that should've picked up at least SOME kind of RF when it's actually touching the plastic fob housing.

I probably was trying to sweep too broad of a frequency range, and the analyzer was passing through the fob's frequency range between pulses - or the fob was frequency-hopping.

I suspect you are right: Frequency hopping. Kind of a surprise they can squeeze THAT much technology into a key fob, huh?

 

I can. Give me 24 hours.

I NEVER thought of this! I have two spectrum analyzers sitting in front of me, one goes to 1 gHz and the other to 50 gHz!!! I'll bring my fob in tomorrow and start looking.

I'd just accepted this limitation, but Wookie's post has me thinking.

Check back tomorrow, guys!

Never mind -- didn't see the page three posts

 

It might seem "snippy" to bring up things such as FCC regulations, but we really do try to keep members within the FCC regulations. The FCC has absolutely no sense of humor if they think one of their regulations has been violated; they are known to throw people in the hoosegow and slap them with hefty fines ($10,000 per incident) for such violations. Tinkering with transmitters can get you in hot water that way.

Receivers, on the other hand, just receive. All I can surmise is that the receiver for your remote keyfob is buried in the car someplace that makes the fob signal hard to get to. The obvious item that comes to mind is to re-orient the antenna for the receiver, or add a new one somehow. It's usually much more effective to improve the receiving antenna than boost the output power of the transmitter anyway.

I have no clue were the fob receiver might be located in your car, or even what it might look like. "Somewhere in the dashboard" would be a likely place. But without a set of manuals, it could be pretty tough to track down.

Then there's the matter of exactly WHICH frequency does the fob transmit on, or does it use spectrum hopping? I can't answer that question. Antennas are generally most efficient if they are tuned to the transmitter's frequency. So, I suggest that finding out where the receiver is located, and determining what the fobs' transmitter frequency or frequencies are would be a good start.

This is a sample of how to respond to a post when you want to interject something OTHER than what the OP's literal question was!

Thanks sarg!

 

I can. Give me 24 hours.

I NEVER thought of this! I have two spectrum analyzers sitting in front of me, one goes to 1 gHz and the other to 50 gHz!!! I'll bring my fob in tomorrow and start looking.

I'd just accepted this limitation, but Wookie's post has me thinking.

Check back tomorrow, guys!

YEAH BABY!!!! This is how this is supposed to work!!!!!

I'm in luuuuuuuuuuuuv with you! (15 posts and a roll of Tumms I might add!)

Does this help? I learned from another thread that you can see the IR light from an LED if you view it with your camera phone!!!

So, My 5 mile range (not literal so coool) key fab and my 3 inch range (again, not literal) all have an IR LED. does that help?

Im the one with idea folks, thats all I bring to the table as of now. but I'm gonna do some reading.

***be sure to have your "homemade transmitter label" made up****

haaha!

 

wr8y,
Good luck with the spectrum analyzers. A few years ago, I briefly tried using a 20GHz HP spectrum analyzer to find the frequency of a fob for a Dodge van.

WELL! You sure called that one. Tried both spectrum analyzers. NOTHING!

We also have a frequency counter that goes to over 40 gHz. (It's an H-P we use as part of doppler traffic Radar calibrations). NOTHING!

The fob simply does not produce enough RF. And I can find NOTHING on the internet to tell us where these things operate. I was thinking that I'd read somewhere that garage door openers are next to the aviation band at around 300 mHz. I'd assumed that key fobs are in that area, too.

So far, I am NOT gettin anywhere. I HATE it when something having to do with radio comes along and I can't find an answer.

 

A-hA! Found some articles on line that mention 288 to 434 mHz for garage door openers.

Then, found this: http://www.cbsnews.com/stories/2004/12/06/tech/main659343.shtml

390mHz !

Now, on to the key fob question... (Not gonna give up.)

 

WELL!
The fob simply does not produce enough RF. And I can find NOTHING on the internet to tell us where these things operate.

Have you looked at post #22 above?

John

 

Oh, and BTW, a few years ago, I used a modified receiver to capture the signal from my Honda key fob and the code is easily read. It is rolling, of course.

John

 

Have you looked at post #22 above?

John

Missed that. I did find 315 and 390 mHz mentioned elsewhere for garage doors.

So, my memory of "300-something" mHz wasn't wrong after all!

 

I coulda Googled it... but that is what "this" site is for right?

Right, Here goes:

I do not understand why the key fob has and actual IR LED. Y'all say it has a Radio Frequency which I know can travel through walls etc?

If LED's require line of sight, Why does it work tucked away in my pocket, I know it has an LED cause I viewed it through my cell phone camera. So, what is the purpose of the IR LED?

The televisions remote will not operate the T.V. if there is so much as a paperbag in the way.

 

Can I remind members to be mindful of the forum rules, particularly item 1.

If the cap fits, wear it. Thank you.

Dave

 

Post 22 nailed it - wish I'd seen it before.

Ok, my spectrum analyzers are simply too insensitive. But my IFR 1200S found my Genie Garage Door Opener on 386.880 mHz and my key fob on 315 mHz.

To answer the original question:
Fine the module in your car that has the FOB receiver in it. In mine, I suspect it would be the security module but it may be the Body Control or Engine Control Module.

See what (if you can tell) it is using for an antenna.

At 315 mHz, you want either a 9 inch or a 17 1/2 inch long antenna. If the antenna (probably just a piece of wire or foil) is shorter than that, extend it! (It is conceiveable that the "antenna" is a SHIELD around other wires that is a few inches long.)

By making this a more efficient antenna, you extend your range without violating any rules.

The other question is, how shielded is this antenna? Did they put the module down in the car where the signal cant' get to it or is it under the dash - where the antenna can run under the plastic dash trim???? Can you (we) get the antenna up to where it can "hear" the signal?

Perhaps this is why your other remote works from up in the building - you are looking down into the car, and getting around the shielding of the door panels, etc.

I'm going to find my module and see what IT is using for an antenna.

I CAN tell you that the key fob puts out as much RF as my garage door opener - the 1200S display shows the same signal level, that is, a level within 3 or 4 dB of the garage door opener.

This tells me that the problem in our cars is the sensitivity of the receiver in the car, NOT the FOB!! Very likely, the lenght or orientation of the antenna is the problem. And I HOPE it is, as this would be a very 'fixable' thing.

I'm glad you asked the question and got me going on this - I now have a little hope of improving mine. And the people in my Crossfire club will be happy IF we can make some improvement in the range of the FOB. This has come up quite often...

No idea on the IR thing - my FOB is obviously RF operated.

 

To answer the original question:
Fine the module in your car that has the FOB receiver in it.

See what (if you can tell) it is using for an antenna..

Im on it!

At 315 mHz, .

Being new, are you saying "milli-hertz"?

By making this a more efficient antenna, you extend your range without violating any rules..

Does the Hz's equate to Power/ transmittal range?


All the cars that are out there, how many "sub"-frequencies
are there?

I CAN tell you that the key fob puts out as much RF as my garage door opener - the 1200S display shows the same signal level, that is, a level within 3 or 4 dB of the garage door opener..

3-4 dB ehy? Cant we boost the dB's without breaking "rules" can we we have a "louder" signal still in the same HZ band?

I'm glad you asked the question and got me going on this - I now have a little hope of improving mine..

And I am glad you are answering it!! What model Mercedes do you have?

No idea on the IR thing - my FOB is obviously RF operated.

Well, it definately has one AND it works in my pocket no LOS.

 

Being new, are you saying "milli-hertz"?

No, Megahertz!

Does the Hz's equate to Power/ transmittal range?

No, this is just the frequency (or "channel") these things operate on.

All the cars that are out there, how many "sub"-frequencies are there?

From what I can tell, 315 mHz for Key Fobs and 390 mHz for garage doors is what the FCC allows for ALL users. Does not sound like there are any other frequencies used - but my knowledge here is limited!

3-4 dB ehy? Cant we boost the dB's without breaking "rules" can we we have a "louder" signal still in the same HZ band?

The dB (decibel) is a unit of measurement used when we compare two signals, or signal levels, or when we specify the gain of an antenna or amplifier.

No, you can't boost this signal without getting into trouble.

But really, you can't boost it ANYWAY. You have a limited amount of battery power, and you SURE don't want to try to piggy back an amplifier on your key fob, do you?

A better way is to improve the performance of the receiver, if possible. I have not torn apart my dash and probably wont - but the antenna on my control module is a little piece of wire. This module and wire are in the "hump" behind my speedometer and Tach. Should I have to replace the bulbs back there, I'll check the orientation and length of that wire.

Getting it out of the bundle of wires and taping it to the bottom of the top of the dash may help. ALSO, making it either 1/4 (8.9 inches) or 1/2 wave (17.8 inches) long (may want to try both lengths, no idea what kind of "matching circuit" the module uses) may also help.

See, receivers work best (as do transmitters) with an antenna a certain length. Commonly, 1/4 or 1/2 wave long wire antennas deliver better performance than just some random piece of wire. Antennas also work much better if they are in the clear, away from other wires, metal, etc.

This is why I say that trying to get the antenna - of what ever form it takes - up away from all the "stuff" it might be around, and adding to it, might be the best answer.

Looking at my service manual tells me NOTHING about how long mine is. But I CAN tell that they have it in a bundle with the harness of wires leaving the module. I strongly suspect I can gain some range by getting it out of the bundle and taping it to the underside of the plastic dash housing behind the instruments.

I suspect your car is much the same. And I'll bet the module is somewhere under the top of the dash.

And I am glad you are answering it!! What model Mercedes do you have?

My car is a "half-breed": a Chrysler Crossfire Roadster. This car is the "obscene love child of the Daimler/Chrysler marriage". Karmin body with a Mercedes engine, transmission and chassis (including the following Mercedes modules: Engine Control Module, Relay Control Module, Security Module, SKREEM (the key fob receiver module), Fan Control Module, Top Control Module, power locks air pump, most of the stuff under the hood.... etc.

 

No, Megahertz!


Looking at my service manual tells me NOTHING about how long mine is. But I CAN tell that they have it in a bundle with the harness of wires leaving the module. I strongly suspect I can gain some range by getting it out of the bundle and taping it to the underside of the plastic dash housing behind the instruments.

Hmmm, well, .... since I am a car dealer in real life I bet I can get ahold of a wiring/component schematic most would not.

I'll work on that and post back!