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Author Topic: RF Transmission  (Read 54452 times)

bph663

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Re: RF Transmission
« Reply #30 on: January 12, 2007, 03:24:56 PM »

Since I rely on these forums to help me out, I'll post my experience and the solution that worked for me.

I had already been using the cm15a and TM751's. I had tried removing the TM751's when I upgraded to the cm15a from the cm11a, but the reception / range of the cm15a wasn't adequate.
I left the TM751's in place.
Then I got the OnAlert plugin to integrate the security devices I already had. The reception range of the cm15a was not adequate, even though my security console had no problems receiving the signals from the security sensors. I tried using an SR731 rf transceiver that I already had from another package deal. But it did not help.

I only had 1 out of 4 door sensors working with the cm15a, and it was the closest, through a few walls and about 20' away.

So I twisted the white antenna tube off of the cm15a, it was not glued, just came off with no problem, leaving the antenna wire visible.
I stripped about 1/4" of insulation from the end of the antenna wire and soldered on a 4 ft wire extension.
I got one of the wires from some phone line I had... 4-conductor solid copper phone line (in-wall type).
I ran the wire from the cm15a (which is plugged into an outlet behind a chair) about 1ft horizontally to the trim of a closet doorway, and then vertically along the edge of the door trim.
The wire is located where the trim meets the wall.
The next closest sensor then started working.
Then I stripped about 2 ft of the insulation from the end of the wire.
All sensors were then working.
I then added a longer length of bare wire to extend up and across the doorway along the edge of the trim.
Distance from antenna to farthest sensor is about 60 ft.






 

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Puck

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Re: RF Transmission
« Reply #31 on: January 12, 2007, 04:19:12 PM »

bph663: Welcome to the forum. Even though what you did here has improved your range (and lets face facts... doing ANYTHING to the CM15A's antenna will improve it), from a technically point of view, if your X10 setup has good reliability it will be purely luck.  ;) Let me explain why.

The receiving methodology of the CM15A is an RSSI receiver (Received Signal Strength Index). What this means is the CM15A measures the ambient RF noise that the antenna picks up, and it compares changes to this in order to extract the X10 signals. With an antenna that is greater than 1/4-wavelength, you introduce the ability of the antenna to pick up lots of unwanted (Non-X10) signals that are outside the 310MHz range. With the length of wire you attached, your antenna is peaking at ~60MHz. You're not far off from the FM radio & CB Radio spectrum. Lots of ambient & transient RF noise. This has the potential to swamp the receiver to the point it can no longer detect changes.

I think you will find that at least doing what teez67f did here, you will get better range and better reliability

My $0.02.  ;)
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bph663

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Re: RF Transmission
« Reply #32 on: January 13, 2007, 11:11:43 AM »

Hi Puck,
Thanks for the link. I had not noticed it before. I'm off to get my cutters!
-b
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Puck

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Re: RF Transmission
« Reply #33 on: January 13, 2007, 11:28:36 AM »

The failure analyst in me comes out now and then I look at ways that things can fail.  ::)

Give the 1/4-wave length addition a try, and if you find your other antenna is still better, then reconnect it. Just wanted to shed some light on the theory behind the receiver and the importance of the correct antenna setup.  ;)

When you add the 1/4-wave addition to the antenna (as per the link), remember that where you have the CM15A plugged in will make a difference in the range for some directions. That's why some of us use the extended coax connected antenna to get it up high and into the most effectice position for our setups. At the same time keeping the CM15A plugged into an clean circuit and having the USB within reach of the PC.

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bph663

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Re: RF Transmission
« Reply #34 on: January 13, 2007, 04:31:11 PM »

Works fine. Thanks for the help and thanks to teez67f for his post.
(I did notice the effects of positioning the antenna - whether in proximity to pc noise or something else, is not always obvious.)
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