RF Experts - Need to pick your brain

[metroplex]

I'm dealing with a 434 MHz two-way car alarm system at home.

I would like to increase the effective range of the transmission for the main alarm module that uses a large antenna. The remote device uses a small antenna similar to the ones you find on 2.4 GHz cordless phones and cell phones. I'm sure I can't do much to increse the range of the remote transmitter/receiver, but I would like to at LEAST boost the transmission range of the main module.

What can I do? Basically I want to be able to receive data from the alarm module from a mile away using this frequency. I don't really need to transmit commands/signals from the remote transmitter at a mile+ range, but it'd be nice.

Any ideas?

 

[AlienCraft]

Why is only one half of a duplex(2 way) circuit all that's important?
What is the make and model?
What is "the main alarm module"? A central Base station?
Is the "small alarm module with the short antenna" the device that goes in whatever you're trying to protect?
How do you know what freq. it's xmitting at?
Short answer is that you will probably be able to add a full wave antenna IF you can make a solder connection with the appropriate size coax to the device circuit board and can mount an antenna somewhere where it'll do some good. The long answer involves determining if only one modification will make a noticeable improvement and the tuning / efficiency of weakest link (remote xmitter)
If it's an extendable - type antenna, it's not going to be optimized for the wavelengths being used. By accurately tuning your rx / tx antennas, you will use every bit of RF transmitter power you have. It will also optimize your ability to reject other freqs. when monitoring.
EZ-Suggestions for improved range / performance... Place as high as possible. Make sure all items are properly gounded... ie no 3rd plugs cut off. Solid , dense items can affect transmission / reception. Consider this when locating items.
Side of hill over looking target = excellent
Inside a steel & brick office building (rx) 5 blocks away from concrete parking structure(tx) = difficult.
Shorter wavelengths are more easily affected
Your mileage may, indeed , vary!

 

[metroplex]

1). Why is only one half of a duplex(2 way) circuit all that's important?

A: Because I don't really need to transmit signals/commands from 1 mile away... I.e. open my power door locks from 1 mile away. I would like to know if someone is breaking into my car from 1 mile away though.

2). What is the make and model?

A:
DEI Responders - the Python/Clifford/Viper.
I.e. Clifford RSX 3.5 - they're all the same.

3). What is "the main alarm module"? A central Base station?

A:
The main alarm module is a brain with a dipole antenna
Picture of Alarm Kit
Look for that weird thing on the bottom of the pic that has 2 things sticking out the sides


4). Is the "small alarm module with the short antenna" the device that goes in whatever you're trying to protect?

A: the short antenna thing would be the remote key fob (also in the above pic).

5). How do you know what freq. it's xmitting at?

A: the owner's manual says 434 MHz or so.

They advertise 1/4 mile range, some people have gotten a range of 10 blocks w/ the car in a parking garage.

I have a hardtop sedan - I'm not sure where to place the antenna for maximum reception but even so, I'd like to figure out a way to boost the range to about a mile if possible.

Compustar advertises a range of 6000 ft with its 900 MHz Spread Spectrum alarm system, BUT my concern is that it will receive interference from the mainstream of consumer electronics that operate on 900 MHz spread spectrum (cordless phones, etc...)

 

[AlienCraft]

The orientation and size make me think they've done some optimization of antenna size. The only thing I can suggest is to put the receiver unit as high as possible in the room to minimize floor reflections.

 

[metroplex]

Well both the alarm brain and the key fob are 2-way systems (Tx/Rx capable), should I place the antenna as high as possible?

There's no way to boost the range (active circuit, etc...) w/o going into complicated designs?


Thanks