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-   -   RI interference on a garage door (http://www.physicsforums.com/showthread.php?t=378406)

davisa Feb15-10 12:09 AM

RI interference on a garage door
 
I'm not an engineer and I figured an EE would be able to help me on this problem. I have a garage door opener that has lost its range due to RI. I've tried everything from powering down my entire house, replacing the mother board, and the remotes and nothing works. I've worked with the manufacturer with no results and there has got to be a answer beside switching to 315 and buying all new remotes and a receiver. Please help.

Can I buy something to find out where the RI is coming from, kinda like a metal detector for RI on this frequency?

This is what I've found and other than this I'm stumped.

"Fine the lines coming into the control head from the manual doorbell switch and the electric eye sensors. You must filter these at the control head by either soldering series inductors in each line to choke the RF or by winding these lines around ferrite toroids. You may also want to try a simpler solution: Place a .01 mf cap cap across the leads at the terminal strip on the main unit."

skeptic2 Feb15-10 08:01 AM

Re: RI interference on a garage door
 
What brand is your garage door opener?
How far is the range?
Where do you live?

davisa Feb15-10 02:26 PM

Re: RI interference on a garage door
 
My garage door is a Chamberlain 1/2 HP model 995XDM. My range is between 1 foot to 7-8 depending on the day. The 7-8 foot range is only when the door is already open. I live in Vacaville Ca which is close to Travis Air Force Base (about 15 miles), so i thought that it was the LMR (Land-Mobile-Radio) system that was causing this but my neighbors don't have this problem.

skeptic2 Feb15-10 06:52 PM

Re: RI interference on a garage door
 
It could be interference caused by the air force base or its possible you may be picking up the 4th harmonic of a nearby FM station. In either case that interference is not going away and you will need to retune both the transmitter and receiver to another frequency.

The second possibility is that the transmitter and receiver are tuned to slightly different frequencies.

The third is that because these are super-regenerative receivers they radiate some noise slightly offset from the frequency they're tuned to. If you have multiple GDOs in the same garage, it's possible one receiver is radiating enough noise to affect the other. If the photo-eye or doorbell wires from the different GDOs are run close together for a distance, this noise from one system can couple into the other and reduce its sensitivity. Putting an inductor in series with or a capacitor across those lines could help. The values you mentioned look reasonable.

To check if the transmitter and receiver are tuned to the same frequency you need to retune the transmitter. There are two main types of transmitters, ones that have rounded corners and ones that are rectangular. I believe the rounded ones have a tuning hole beneath the label on the back. If you poke at the label you can find the hole. Any metal near the transmitter will detune it slightly so it's better to use a non-metallic screwdriver if you can find one. If not, you'll have to remove the screwdriver from the tuning hole before testing it. Insert your tuning tool and try turning the adjustment very slightly. Then try the transmitter and note if the range is better worse. If worse, try going in the other direction only a small amount. In other words, try to find the spot with the best range.

The rectangular transmitter has a screw that holds it together located underneath the label but the tuning is the same.

If that doesn't work, you may try retuning the receiver. The receiver tunes by screwing in or out a ferrite slug. The the tuning hole is behind the label and you'll have to hunt for the hole by poking the label. Normally a non-metallic hexagonal tuning tool is used. If you don't have one you could try using an allen wrench. Remember to remove the allen wrench before checking the frequency with the transmitter. Ferrite is fragile so when you're tuning, don't try to turn it with more than a slight force. It should turn easily. Once you've moved the receiver frequency, slowly adjust the transmitter until the GDO works and adjust for best range.

Let me know if any of these suggestions works.


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