MHz Calculation

[Se7en]

This thread doesn't belong in the Amateur radio antenna category but I couldn't think of a better place.

Key Fob (wireless remote to unlock vehicle) question.

I have a Aftermarket alarm with two keyfobs. Both have brand new battery's.

Problem: I have to be with in 10' or less to activate door locks and or alarm.
Where would the antenna be located; main alarm box or key fob? ( of course they both have antennas) proceed to next step.

Would it be more effective to Calculate the Frequency of the transmitter and or Receiver using this calculator: Frequency Wavelength Calculator and install the antenna or will any random length work ?

I am going to guess that it possibly transmits somewhere on 300MHz (wikipedia).

What Does a SMD antenna look like on a tiny circuit board of a key fob?

Solution? [-------------------].

Several years ago i had a VW Golf that had the same problem i didn't have a calculation to use or Google and just ran a long wire in the ceiling of the vehicle (range was up to 100' +)

 

[Se7en]

After more research that low power devises normally run at 2.5GHz and up, beats me why wiki says 300MHz.
makes more sense, since even a 1/4 wave antenna at 300MHz is way long even for a small device the size of silver dollar, that just doesn't sound cost effective..etc

 

[Se7en]

After more Research i found this: http://scytek.net/manuals/galaxy/g20.pdf

 

[Captain Kilowatt]

A lot of after market alarms ran on or near 312 MHz. I think I took out mine by transmitting 50 watts in the 155-156 MHz range. I suspect maybe the second harmonic was strong and only a couple feet away. That was many years ago.
why not try what worked before? Nothing to lose.As for a microstrip antenna, they simply look like a circuit trace often zig zag or folded back on itself.

 

[Captain Kilowatt]

A lot of after market alarms ran on or near 312 MHz. I think I took out mine by transmitting 50 watts in the 155-156 MHz range. I suspect maybe the second harmonic was strong and only a couple feet away. That was many years ago.
why not try what worked before? Nothing to lose.As for a microstrip antenna, they simply look like a circuit trace often zig zag or folded back on itself.

BTW why do you need to be so far away to lock/unlock? Most people do so as they get up to the vehicle. My OEM alarm works up to a couple hundred feet. It is great for locating the vehicle in a crowded parking lot when you forget where you parked.

 

[Se7en]

BTW why do you need to be so far away to lock/unlock? It is great for locating the vehicle in a crowded parking lot when you forget where you parked.

There. Ill lurk under the dash for the alarm and fins the antenna and just extend it like I did before on the other mobile.

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[BOOTY MONSTER]

a 2 driving 4 pill joe made amp will get that keyfob TX'ing down the road . or scale down the merlin antenna for that frequency and you'll get up to 90 db more signal from it .
personally .. i'd do both

 

[Captain Kilowatt]

Chances are that a 2 driving 4 pill joe made amp is already transmitting on the same freq the keyfob is. And all others as well.

 

[NeoHam]

Wow

Are you saying a remote lock system can be destroyed by transmitting ham? It never even crossed my mind. Has this been documented somewhere?

 

[Beetle]

Most keyfobs operate somewhere around 310-315 MHz. And they can be interfered with. Just yesterday, I couldn't get mine to operate at all, either up close or 100 feet away. Just on a hunch I called a friend of mine at work in the Naval Shipyard here and asked if a particular system was being tested at that time.

"Can't use your remote car unlocker thingy, Beetle?" was his reply. He said to wait about 20 minutes and try again. I did, and it worked fine. At the time, I was in a parking lot, high on a hill (at school), and line of sight to the shipyard. If I were in my own driveway, I'd be in the shadow of another hill and the keyfob "thingy" would be unaffected.

 

[Captain Kilowatt]

Are you saying a remote lock system can be destroyed by transmitting ham? It never even crossed my mind. Has this been documented somewhere?

I was only surmising that was the problem. After I found my after market alarm was not working I began to search for a reason and found out it operated on 312 MHz. I used to operate in the high end of 155 MHz with 50 watts or so. Second harmonic was 311-312 MHz and since the alarm stopped working a few weeks after I started using that freq it was a logical conclusion that the front end of the alarm receiver was taken out by the RF.

As for what Beetle mentioned, I remember reading about some areas that had a radar installation nearby and when certain systems were being operated locals could not use their remote garage door openers.

 

[Se7en]

a 2 driving 4 pill joe made amp will get that keyfob TX'ing down the road . or scale down the merlin antenna for that frequency and you'll get up to 90 db more signal from it .
personally .. i'd do both

LoL !

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