Making an antenna for an electronic reciever, any ideas?

[Stand_watie]

Another question for the gallery, perhaps we have some electronic guys who can help me with this.

I have a driveway alarm system that consists of a pair of motion sensor/transmitters and a receiver/doorbell chime. The box claims that it is good up to four hundred feet, and it indeed is, when there is nothing in the way. The distance from the end of my driveway to the road is a little less than that, and from just outside the door of the house to the road it will transmit/receive just fine. The problem is that inside the house the distance that it will receive from is halved.

So what I think I need is an antenna (for a device that has no sort of an antenna attachment) going from the receiver to the outside of the house.

If that is unfeasible, I guess I'll have to mount the receiver outside of the house and run a hardwire from the receiver to a speaker inside the house.

Ideas for either?

[Azrael256]

Any idea what frequency it operates on?  If it's something nice and standard like the 2.4GHz range, there are literally thousands of manufactured antenna options so you won't have to rig up something.  An outdoor WiFi antenna would work fine.  You'd have to open up the box, but it wouldn' be too difficult.

There'll be something in the manual about frequency.

[Stand_watie]

Any idea what frequency it operates on?  If it's something nice and standard like the 2.4GHz range, there are literally thousands of manufactured antenna options so you won't have to rig up something.  An outdoor WiFi antenna would work fine.  You'd have to open up the box, but it wouldn' be too difficult.

There'll be something in the manual about frequency.

It's 434 MHz.

This is the particular brand here


http://www.drivewaypatrol.co.nz/

[mfree]

IIRC, a vertical wire half the wavelength of the signal and a ground path (metal stake in the ground) directly beneath should do it.

[Stand_watie]

IIRC, a vertical wire half the wavelength of the signal and a ground path (metal stake in the ground) directly beneath should do it.

My friend, perhaps I sounded too knowledgeable in my original post, because your response reads to me like you're assuming electronic understanding that I don't have.

By "half the wavelength" do you mean a wire that is 217 feet long? Or do certain gauges of wire correspond to certain wavelengths? How do I connect this wire to the receiver?

[Azrael256]

Nah, about a foot of wire would be half the wavelength.  Maybe a little more.  I'm too tired (and lazy.  Yes, lazy.  Screw you, hippie, it's Saturday.) to do the calculation.  I know that those old 466mHz cordless phones had a wavelength that was right at 2'.

Grounding it wouldn't hurt, either, but I see that it's battery operated, so that may be trickier than it sounds.  You'd need to attach extra antenna length to the antenna inside the box (or, alternatively, uncoil any internal antenna and hang it in a window).  With a wavelength that short, there won't be an antenna coil inside (as in ferrite coil.  A bunch of wire wrapped around an iron bar), just a length of wire *somewhere*.  It'll be a length of at least a foot that seems to go off to nowhere.  It might even be printed on a circuit board.  If you open it up and take a decent photo of it, it'll be easy to identify.  Just adding length to an antenna will help, but it's always best to add it in relation to the wavelength to get good results.

Just so you know, modification will completely void the warranty.

BTW, wavelength is calculated by dividing the speed of light by the frequency.  So if the speed of light is roughly 30,000,000,000 cm/sec and the frequency is 434 million cycles per second (30 billion divided by 434 million), we get a wavelength of about 69cm, which is...  uh, about 27".  

Dammit, I did the calculation anyway.

[Nathaniel Firethorn]

http://m2inc.safeshopper.com/5/cat5.htm?395

If you want directionality.

- NF

[Headless Thompson Gunner]

The device has to have some sort of antenna already, else it wouldn't be able to transmit.  If you don't see an antenna on the outside, nor any connection jack for an external antenna, then the antenna has to be something internal to the device.  

If that's the case, then you'll have to open the thing up, locate the antenna, and de-solder it and solder a newer/better antena in its place.  It sounds like this is more work than you want.  

Most manufacturers of radio transmision equipment build their devices this way specifically to prevent you from increasing their transmission power and range.  If the device's transmission power is too great it could land the manufacturer in hot water with the FCC.

Basically you're SOL.

[roo_ster]

Most manufacturers of radio transmision equipment build their devices this way specifically to prevent you from increasing their transmission power and range.  If the device's transmission power is too great it could land the manufacturer in hot water with the FCC.

Basically you're SOL.

WRT54 Linksys router being the lovely exception to that rule.