Installing a 315MHz Garage Door Antenna Extension

Hi folks! I have two Liftmaster LM3800 garage door openers, which are jackshaft openers that get mounted on a front torsion spring:

LiftMaster LM3800 - Album on Imgur

The range of the built-in "antenna" is terrible - there are MANY complaints about its range online. If you look at the pictures, you'll see one long purple wire hanging straight(ish) down, and one short wire bent off to the side at a right angle(ish).

So I ordered two Liftmaster antenna extension kits. The kit contents are shown in the second picture. It's an L bracket, an antenna, and a coax cable. However, the installation instructions say to cut off one end of the coax, unwind some outer braid, attach the braid to a ground source inside the opener, and solder the end of the inside coax conductor to the end of the long purple wire.

Quite frankly, this sounds like a dreadfully horrible way to install it.

What I'd like to is to drill a hole and mount a male F jack somewhere on the opener. However, I'm not sure of the best electrical method for doing this. (I'm a digital electronics E.E. and all my analog knowledge drained out of my brain 20 years ago!)

I see 75/300 baluns that have two two screw terminals. Is that the proper way? Which is appropriate, a 1:1 balun or 4:1 balun? Does the right answer depend on how the board-level impedance was designed? What's the purpose of the short purple wire? Is it possibly the same as ground? (I can't tell without removing the board, which isn't trivial.)

I included a picture of the antenna length. The openers operate at 315MHz. Is this a suboptimal antenna design? If I can do better, I'm all for throwing some/all of this kit away and doing it right.

Another question - I have two openers and need two antenna extensions. Are there any restrictions on how the two remote antennas are mounted? Do I need to maintain any minimum separation distance, etc.?

All advice is appreciated. Thanks everyone!

Wow, exact same question

Ok, like you I have a 3800 opener, determined 315Mhz, am a former life digital EE, but remember enough analog to think that the directions from Liftmaster are odd at best.

Have you tried anything out?

Do you know what the 2nd antenna on the board is for?

Feel free to reach out by email - misc at ferrythecat dot com

CK

Those lift-master install instructions are indeed odd.
Maybe the 2nd purple is for another add-on wall device to talk to a router in the home for Wifi app-openers??

Get it outside

The way I'm reading your post, the purple wires are the antenna.
If so, and it was my garage opener, I'd first attach a lotta wire to the end of the purple wires, and get it high and outside, and see how it flies. Since it's a receive antenna, the match isn't critical.

If that don't help, then go the route you're thinking about.

The two antennas make it look like a dual diversity receiver. In other words, multipath can be an issue, so using two receive antennas and picking the one with the best signal is often done. Some WiFi routers use this, some wireless microphone bases use this also.

You could pick one of the purple leads and strip it back and connect it to the center lead of your female F connector. The outer ring of the F connector would ideally be connected to the frame of the opener, which should be grounded.

Could also be just repositioning one of the purple leads might help, too.

If it was me, I'd probably do something excessive like install 2 antenna jacks, one for each of the purple wires. I'd run two coaxial cables in opposite directions from the opener and install 2 simple ground plane 1/4 wave antennas. If you garage is covered in aluminum siding, any sort of metal siding, foil based insulation, or any RF blocking material, I'd install the antenna(s) outside.

I've had this Maxrad 315Mhz fiberglass base antenna with N connector sitting in my garage rafters for years and could never find a use for it. Maybe I should connect it to my garage door opener....
prcguy

Interesting. I recently had new door openers installed and am pushing the envelope to see how far away I can open the doors.

It's over half a block around the corner.

Always handy in case you bump it while leaving and can't see if the door opened or not. Or wait to close it and are not sure if it closed or not.

While I can see the benefit of extended range, range out of view is risky without a return confirmation signal.

ampulman can use the MyQ (if it works with his opener) and his RF garage door remote around the corner. MyQ will send the close/open text to his smartphone,etc.

The liftmaster MyQ is the best app for garage door users with smartphones with internet connection.
It has the option to text you everytime it opens/closes. It works great!
Open the garage door when you are away from the home. Let xx into the garage for any reason.
https://www.liftmaster.com/For-Homes/MyQ-Connected-Home

Just remember that anyone else with a 315 MHz master transmitter also can open your garage door from that extended distance.

Karl-NVW said:

Just remember that anyone else with a 315 MHz master transmitter also can open your garage door from that extended distance.

Click to expand...

Funny thing, the OP hasn't been on since he posted eight months ago. Go figure.
Larry