Passive RF repeater?

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KitCarlson
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Posted by KitCarlson: Wed. Aug 17, 2011 - 02:40 PM
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I recently installed a garage door opener in an arch style metal building. The building is an excellent RF shield when closed. I am able to operate the control for a few hundred feet with the door open and only a few feet with the door closed.

The remote control operates at 515MHZ. I am considering using a coax cable and folding back 9.4" of the shield on both ends exposing 9.4" of the insulated conductor. I will then place one end near opener and the other on the outside of building.

Will this work? Is there a better way? I hope to get 50' with door closed. Just trying to make a good plan before I climb around using the 16' step ladder with my old tired body.

It all starts with a mental vision.

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Learning and Information, General Electronics
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ka7ehk
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Posted by ka7ehk: Wed. Aug 17, 2011 - 03:11 PM
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That may, in fact, work.

Jim

 

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gregsmithcts
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Posted by gregsmithcts: Wed. Aug 17, 2011 - 03:18 PM
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Why 9.4"? Wouldn't 5.7" represent a 1/4 wave length?

--greg
Still learning, don't shout at me, educate me.
Starting the fire is easy; the hardest part is learning how to keep the flame!

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DO1THL
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Posted by DO1THL: Wed. Aug 17, 2011 - 04:10 PM
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In addition, i seem to remember, you may also have to adjust the actual length of coax cable between both ends to be exactly - now what... lambda/2 or lambda/4? Damn, as a licensed radio ham i once was supposed to know... Ok, passed the exam ;-)

Einstein was right: "Two things are unlimited: the universe and the human stupidity. But i'm not quite sure about the former..."

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KitCarlson
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Posted by KitCarlson: Wed. Aug 17, 2011 - 06:22 PM
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I think 1/2 wave length is for dipole, 1/4 antenna with ground plane. That makes me wonder if I could simply use a bolt hole with nylon insulator, then fix a 9.4" solid wire half way out for 4.7" on each end. The building metal will serve for ground planes, no transmission line. RF experts, will this work?

It all starts with a mental vision.

Last Edited: Wed. Aug 17, 2011 - 07:19 PM
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DocJC
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Posted by DocJC: Wed. Aug 17, 2011 - 06:46 PM
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If the RF unit is separate from the rest of the mechanics perhaps you could put the RF unit in a weatherproof enclosure on the outside of the building.

Run just the contact closure twin-lead into the mechanical part of the door opener, inside the building.

Mount the unit outside where it is difficult for anyone to tamper with it, depending upon the security requirements for the building and access.

JC

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Plons
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Posted by Plons: Wed. Aug 17, 2011 - 07:38 PM
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My math ended up in 11.4" for lambda/2. And for this application I suggest lambda/2 at both sides
Instead if solid wire, how about copper pipe as plumbers use ?

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gregsmithcts
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Posted by gregsmithcts: Wed. Aug 17, 2011 - 09:06 PM
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Quote:
My math ended up in 11.4" for lambda/2.
Mine too (see above)... I still don't know where the 9.4 is coming from?

--greg
Still learning, don't shout at me, educate me.
Starting the fire is easy; the hardest part is learning how to keep the flame!

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KitCarlson
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Posted by KitCarlson: Wed. Aug 17, 2011 - 10:35 PM
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Thanks, I made an error. I will give it a try and report back.

It all starts with a mental vision.

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KitCarlson
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Posted by KitCarlson: Wed. Aug 17, 2011 - 11:25 PM
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It works great! I also made a frequency error, it is 313 MHz, not 515MHz.

I used a 3' brass welding rod. The bushing was made by drilling out a large drive-in nylon rivet. The rod was bent slightly at both sides of the rivet to retain the rod in the center.

Thanks for comments, they helped make the project a success.

It all starts with a mental vision.

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Jeckson
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Posted by Jeckson: Thu. Aug 18, 2011 - 08:52 AM
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KitCarlson..

Is that repeater?

RF---RF-another RF---another RF.

Jeckson

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Plons
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Posted by Plons: Thu. Aug 18, 2011 - 09:26 AM
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No. As the thread-title says: it's a passive RF-repeater. KitCarlson created a gateway for his RF-remote with the 3' brass welding rod.

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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KKP
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Posted by KKP: Thu. Aug 18, 2011 - 04:39 PM
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This is also an excellent example of what happens when you put your PCB inside a conductive box, and forget to filter that one wire where it passes through the shield.

KitCarlson has punched a meter-sized (electrically) hole in the building. If you punch a meter-sized hole in your conductive box, most likely it's entirely gone.

/Kasper

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