Antenna for a garage door opener.

[ljcox]

My garage door opener has a 433 MHz receiver. But it only has a simple wire antenna so I need to be close to the garage in order to open or close the door from the car.

I would like to make an antenna that has some gain. But I'm wondering how to match the antenna to the receiver. Any advice will be appreciated.

 

[rjenkinsgb]

"Gain" in an antenna is achieved by making it directional, like adding a reflector or lens to a lamp boosts the output in one way at the expense of another.

Possibly just a simple omnidirectional ground plane antenna would be OK; the receiver input is almost certainly designed for 50 ohms or somewhere around that.

Is the garage door metal? If so, mounting the antenna higher so it's not screened may help.

If you can fit a 50 Ohm BNC socket to the door opener, it would make it easy to swap antennas for testing, or just back to a wire antenna directly in a plug so it still works inbetween other tests. Connect it with a short length of coax, with the screen/braid to whatever ground in nearest the antenna connecting pad.

Plus having a BNC socket bolted in the ground plane makes a good attachment for the wire element, compared to a loose coax end..

Either way, that or soldered coax:

Try it with some good quality 50 Ohm coax to a suitable nearby location. Use a bit of metal sheet, or even aluminium foil stuck to cardboard as the ground plane connected to the screen, with a 1/4 or 3/4 wave stiff copper wire connected to the coax inner, set straight out from that.

If the garage is high enough, fit the antenna upside down so the ground plane is horizontal with the element hanging below. The radiation angle from a normal upright one is somewhat upwards - fitting it upside down makes it most sensitive slightly downward instead.

One wavelength at 433 MHz is around 692mm. The element length from the ground plane should be either 1/4 or 3/4 of that then less 5%.

 

[ljcox]

Thanks for the reply. Yes, the garage door is metal, but the antenna wire projects above the ceiling & the front wall is brick.

So I'll do as you suggested - make a ground plane & mount it upside down just under the roof peak.

How big does the ground plane need to be? 1/4 wave, 1/2 wave or is it not critical?

 

[crutschow]

A 433MHz or TV UHF directional antenna should help.
You would need to use coax from the opener to the antenna with a Balun to convert from the single-ended coax to the balanced antenna (twin-lead) connection.
If you want to roll your own, here's an example.

 

[ljcox]

A 433MHz or TV UHF directional antenna should help.
You would need to use coax from the opener to the antenna with a Balun to convert from the single-ended coax to the balanced antenna (twin-lead) connection.
If you want to roll your own, here's an example.

Thanks for the comment, but I also need a reasonable reception from the house side of the garage as we often open or close the door using remote from the kitchen. I think the ground plane idea will suit me better.

 

[rjenkinsgb]

It can be as large as you like, as long as it is at least a half wave edge-to-edge.

 

[ljcox]

It can be as large as you like, as long as it is at least a half wave edge-to-edge.

Thanks, I've noted that.

 

[JimB]

I would like to point out that the "ground plane" part of a groundplane antenna does not have to be a solid plate.

Look at these two antennas here:

the ground plane is simply four rods, sticking out horizontally.

And here they are, seen from outside the aircraft, a Zeppelin.

JimB

 

[ljcox]

Thanks. Yes, I recall seeing such an antenna mounted on a tall pole with that type of ground plane.

 

[Nigel Goodwin]

Thanks. Yes, I recall seeing such an antenna mounted on a tall pole with that type of ground plane.

Yes, not as good as a full solid ground plane, but 'good enough'

 

[ljcox]

Thanks Nigel. I have decided to use a sheet of aluminium as it seemed easier to build that the 4 rods.

And if it works better, that's excellent.

 

[unclejed613]

i regularly talk on a 2 meter ham repeater that's 40 miles away using a ground plane antenna made from a BNC panel mount connector and 5 pieces of brazing wire, one (the vertical) soldered to the center pin of the connector, and the 4 ground plane elements soldered to the screw mounting holes of the BNC connector... the repeater is 40 miles away and i can hit it with a 1 watt radio with full quieting.

 

[ljcox]

Thanks for the suggestion.
I don't know what power the remote transmitters output, but I only want the extend the rang to about 50 metre.
So ground plane antenna should do the trick.

 

[upand_at_them]

I remember seeing somewhere online where the guy ran coax to outside of the garage and had a dipole.

 

[ljcox]

I remember seeing somewhere online where the guy ran coax to outside of the garage and had a dipole.

Thanks, that is another option I'll consider when I'm ready to do the job.