X10 Community Forum
🔌General Home Automation => Automating Your House => User Modified Devices => Topic started by: Frank3d on October 11, 2010, 03:04:41 PM
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I checked the CM15A threads and I can’t find where anyone mentions that there are two separate antennas on the CM15A, one for RX the small outside whip and one for TX a short wire on the inside of the unit. I would like to propose a dual antenna design or a combiner / splitter much like one mentioned in earlier posts to combine two external antennas but in this case to combine the TX and RX signals from the CM15A into one strategically placed outside 1/4 wave groundplane antenna cut to 310Mhz. My only concern with the splitter used as a combiner is it’s possible the TX RF power might hurt the receiver input if combined with it using a 50ohm splitter for 310Mhz. Otherwise the only alternative is two individual antennas one for the TX and one for the RX to really get max RX and TX data to and from the CM15A.
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Yes the CM15A has a separate daughter board for transmit and receiving. Each board has its own antenna. The receive one is the external one and the transmit is the one glued to the case internally.
I don't think there was a great interest in adding an external transmit antenna to a CM15A.
Since you have searched the threads you probably have found the CM15A schematic link to the FCC Database.
http://kbase.x10.com/wiki/Schematics
B4S CM15A
I don't see any protection on the receivers antenna input and I don't think the Himark RX3310 chip has any protection internally.
The transmit circuit also doesn't look to rugged.
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Agreed............. I have not yet tested the TX range of the CM15A it might be adequate for my application. I need camera control that makes use of the CM15A's TX that’s why I was in question why nothing has been mentioned about a TX antenna for control applications. And yes I have seen the CM15A's schematic on the FCC site.
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My only concern with the splitter used as a combiner is it’s possible the TX RF power might hurt the receiver input if combined with it using a 50ohm splitter for 310Mhz. Otherwise the only alternative is two individual antennas one for the TX and one for the RX to really get max RX and TX data to and from the CM15A.
Probably two antennas is the best way to go. My guess is; the losses through a combiner will negate all advantage (especially on the receive side) that a "better" TX antenna could give you. Besides, how does a combiner work where TX and RX frequency is the same?
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That was my major concern. There would be only minor isolation between the RX port and the TX port using a splitter meaning TX power would be at the RX port 3db down possibly causing damage to the receiver first rf amp. Unlike a standard commercial repeater duplexer that filters the tx pwr from getting to the rx port when using a single antenna for RX and TX. This can only be done if the rx frequency is not the same as the TX frequency unlike X10 that uses 310Mhz for both TX and RX however the CM15A's TX and RX do not occur at the same time as it does with a commercial duplexer that acts as a combiner to use one antenna for both TX and RX. To be safe I will use two antennas, one for TX and another for RX. Buy the way when using a standard splitter in reverse as a two signal combiner which can be done under certain circumstances usually there is only a 3db loss on each port.
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Then you must also realize. Modifying the CM15A in any manor. Voids the FCC Type Acceptance.
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And X10's warranty.............................
End of subject.
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I had replied to your other [identical] post.
I checked the CM15A threads and I can’t find where anyone mentions that there are two separate antennas on the CM15A, one for RX the small outside whip and one for TX a short wire on the inside of the unit.
Here's one: http://forums.x10.com/index.php?topic=17240.msg94900#msg94900
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Aside from FCC certificate for CM15A design, but the warranty issue can be resolved with passive antenna (coupling). I added such an antenna to my CM15A and suddenly all wireless problems were gone. That opened another box of issues that are related to X10 software, general design issue etc. If interested, please let me know and I will post the modifications with some photos.
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I added such an antenna to my CM15A and suddenly all wireless problems were gone. That opened another box of issues that are related to X10 software, general design issue etc. If interested, please let me know and I will post the modifications with some photos.
Pictures are always nice!
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Then you must also realize. Modifying the CM15A in any manor. Voids the FCC Type Acceptance.
Apologies for replying to such an old and dormant thread but I just got here. ;)
There is no FCC issue with improving the receiving antenna. It's a simple way to improve reception. And, since the CM15A is isolated from the mains by the power supply transformer, you can even make a direct connection to the receiver. Here's a simple, easily made antenna http://davehouston.org/eggbeater.htm (http://davehouston.org/eggbeater.htm) that will work wonders for most CM15A users. You can even add a wideband preamp at the antenna to make it even better.
The FCC does prohibit any modification of the transmitting antenna.
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Then you must also realize. Modifying the CM15A in any manor. Voids the FCC Type Acceptance.
Apologies for replying to such an old and dormant thread but I just got here. ;)
There is no FCC issue with improving the receiving antenna. It's a simple way to improve reception. And, since the CM15A is isolated from the mains by the power supply transformer, you can even make a direct connection to the receiver. Here's a simple, easily made antenna http://davehouston.org/eggbeater.htm (http://davehouston.org/eggbeater.htm) that will work wonders for most CM15A users. You can even add a wideband preamp at the antenna to make it even better.
The FCC does prohibit any modification of the transmitting antenna.
You are Dave Houston of http://davehouston.org fame! ;D
Glad you're here Dave.
Your contributions to Home Automation and X10 are legendary!
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I was referring to the Transmit antenna and may have not been clear.