Wireless Network

Discussion in 'C-Bus Toolkit and C-Gate Software' started by Thomas, May 18, 2006.

  1. Thomas

    Thomas

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    Hi everyone,

    Firstly, please accept my apologies, should this be posted on the wrong forum.

    I believe that there a couple of wireless installation out in Oz, and I hope that someone may be able to point me in the right direction to diagnose a problem:

    I have a dual network, one being wired, the other wireless. Both communicate with each other via the gateway, and all has been well up until a few weeks back. What seems to be happening is that the wireless network goes off-line, that is it will not communicate with the wired network, and also not with other units on the wireless side.

    When I scan in the networks during times when the comms have failed, I still see as much as the gateway on both sides, but the entire wireless network is gone. Also not status info can be extracted on the wireless side. Which makes sense. This leads me to believe that it is not radio interference, but rather a component failure.

    Naturally, once the network is functioning again, all info is displayed.

    Unfortunately, while I assume that the gateway is taking intermittent holidays, I cannot be sure of that.
    I would therefore appreciate any advise and info to help me resolve this matter.

    Thanks
    Thomas
     
    Thomas, May 18, 2006
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  2. Thomas

    2dogs

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    I would say it is definate RF interference. The gateway being the only unit you can see (when there is the comms failure) confirms this. I have had this as well.

    Start looking for the RF source.
     
    2dogs, May 26, 2006
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  3. Thomas

    TheDuck

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    Do you have other wireless devices operating at your site? Maybe something that does not communicate all of the time.
     
    TheDuck, May 26, 2006
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  4. Thomas

    Thomas

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    Looks like it

    Thank you for your replies. I have been trying to get to the bottom of this, and have to thank especially Ashleigh for his continued support.
    Though the matter is not really resolved, the interference seems to have almost disappeared. I have other equipment as well which operates at the same frequency, namely a Paradox Security system, but the two of them have been living happily next to each other for almost a year.
    I have no idea where the interference might be coming from, and can only add that the Paradox system has been runing without a hiccup.
    And odd as it may seem, the only activity in the area has been by our Power Supply Company, which has now completed the section of power lines closest to our premises (1 km away), and things are looking almost normal again.

    Thanks again
    Thomas
     
    Thomas, May 27, 2006
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  5. Thomas

    TheDuck

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    Keep in Touch

    Well you are dealing with the right person, please keep us informed of any other issues occurring. The new powerline work is a bit hard to put it down to but time will tell.
    Interesting coment about the wireless alarm we have worked the Clipsal Homesafe Alarm product along side to C-Bus Wireless without issue although the boys at CIS Tech Support tell me it opperates at 303Mhz.:D

    Cheers
     
    TheDuck, May 29, 2006
    #5
  6. Thomas

    Roti

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    Hi.

    I get interference from wireless headphones. They are Sennheiser RS65's which are meant to work at 925-926.5 MHz (nowhere near the C-bus wireless range or multiples of it). All base stations (3 of them) do the same thing. Switch them off and all C-bus works fine. Turn them on and nothing communicates within about 20m.
     
    Roti, Jun 5, 2006
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  7. Thomas

    Don

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    Are you sure about that frequency? The distance you are experiencing interference over seems far too high to be the result of overloading the wireless C-Bus receivers. I just checked the site of an Australian distributor and it looks like those headphones may be 433MHz:

    http://www.syntec.com.au/*ws4d-db-query-QuickShow.ws4d?SNRS65

    Wireless C-Bus transcievers incorporate an RF SAW preselector filter, so are very immune to out-of-band interference. It's only the in-band signals that can be a problem.

    Don
     
    Don, Jun 6, 2006
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  8. Thomas

    ashleigh Moderator

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    Those wireless headphones will be illegal in many countries, and may even be illegal in Australia.

    Use of the unlicensed band for continuous transmission of voice or music is often prohibited.

    Sadly, it's a case of buyer beware with these things.:mad:
     
    ashleigh, Jun 6, 2006
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  9. Thomas

    Thomas

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    Wow!

    Hi Roti, Don, Ashleigh,

    Guess what... I have the same headphones, and gave them to my son to hook up to his PC. So when he plays, we are down. Just confirmed this, and also confirmed that the stated frequency of these headphones is 434 MHz. You can also hear the signal being disturbed in the headphones when you press any of the C-Bus buttons.

    It has to be noted that the wireless Paradox system works fine despite the headphones, so now one might ask if it is primarily RFi or immunity, or both?

    Either way, I'll get some wired headset for the lighty, and the problem will be gone.
    Thank you all, especially Roti.

    Cheers
    Thomas
     
    Thomas, Jun 6, 2006
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  10. Thomas

    ashleigh Moderator

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    Well its sort of RFi / immunity. The cause is simply that the headphones and the cbus wireless operate at the same frequency... but read on...

    Cbus wireless and your alarm system are both "well behaved" because they transmit small packets in periodic bursts.

    The headphones, on the other hand, are "anti-social cretins" because they transmit continuously.

    Its the continuous transmission that screws up anything else on the same frequency.

    Cbus wireless has a narrow band front-end RF filter with extremely good rejection of unwanted frequencies (part of the reason the transceiver in it costs so many $). However, the front end filter does nothing for in-band interferers, which is what your continuously transmitting headphones will do.

    The effect for cbus wireless is to cause the adaptive noise-floor it uses to be rasied - which means it will still work, but the range will be reduced. Provided the power at the receiver due other cbus wireless is significant greater than the received power due to the headphones, it will work. Otherwise it won't. The in-band signal powers are additive... (and thats why I went to University for umpteen years!!!)

    So - short answer - don't use continuous transmitting devices that run in the same frequency band.
     
    ashleigh, Jun 6, 2006
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  11. Thomas

    Roti

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    That explains a lot!

    I was looking at (wrong) reference docs from an overseas site (they use a different range on some overseas models as seen on the top right of the ref page you provided)
    http://www.syntec.com.au/aaaStoreFronts/Syntec/PDF/SNRS65.pdf

    Thanks for correcting me. Bummer about the headphones though - I really like(d) them.

    Next questions -

    1) Can anyone recommend good quality wireless headphones that don't interfere with C-bus in Australia?
    2) Anyone without C-bus Wireless want to buy some slightly used wireless headphones ;-) ?

    Maybe someone should create a sticky on the forum to start listing/collecting devices encountered that interefere.
     
    Roti, Jun 6, 2006
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  12. Thomas

    Thomas

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    Hi Ashleigh,
    thanks for that additional information. I wouldn't have thought of checking the frequency of these headphones when I bought them many years back. One assumes that a reputable manufacturer sticks to the rules of the game. After all, we are not talking about some chinese junk, but expensive equipment. I am wondering if the 434 (yes!) MHz is supposed to circumvent the interference issue on 433 MHz. Obviously that didn't work.
    But to sum it up for me, while I never thought of this being the problem, I am more amazed that someone else in the world also has C-Bus Wireless, AND uses the same make and model of headsets. What are the odds of that happening?:)
     
    Thomas, Jun 6, 2006
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  13. Thomas

    MichaelCarey

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    As an active "ham" operator, another possible cause of interference to C-Bus Wireless are licenced users of the Amateur Radio service.
    C-Bus Wireless uses 433 MHz, which is part of the 70CM (420-450MHz) band which was rudely hijacked by the ACA/ACMA a few years ago to create the LIPD band 433.050 to 434.790 MHz.
    Check out this link, scroll down to 70CM band :-
    http://www.wia.org.au/bandplans/Australian Amateur Band Plans 2005-10.pdf
    Amateur radio operation in this band is secondary to the radio location service, PLUS we have no protection from "interference" caused by LIPD's, I look after a 70cm radio repeater that quite often gets interference from LIPD's. Some government desk-jockey thought that putting class licenced devices in the long established (30 years+) "repeater input" section of the 70CM band plan was a wonderful idea. :mad: :mad: :mad:
    Amateur Radio Operators are allowed to transmit up to 120 Watts FM/AM (400 Watts peak SSB) throughout this band with many common FM transceivers transmitting up to 50 Watts. Someone operating quite some distance away could obliterate a C-Bus Wireless network, and not be affected the other way.
    Just as licenced "ham" operators have no protection from interference from LIPD devices, LIPD's (including C-Bus Wireless) have no protection from licenced users of the 70CM band. Even if you found out who was causing the problem, there is probably nothing you can do about it.
    One of the joys of using a shared radio spectrum! :)
     
    MichaelCarey, Jun 6, 2006
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  14. Thomas

    ashleigh Moderator

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    Indeed.

    To reiterate an earlier point - this is the main reason we have a damn fine front end RF filter in cbus wireless. It helps hugely with out-of-band rejection.

    FYI, the nominal frequency of cbus wireless is 433.92 MHz.

    Those headphones at 434 MHz are probably blasting away at a couple of milliwatts, without a great deal of attention to the occupied bandwidth. It does not take much effort to drift off by a few 10's of kHz.

    Compare this frequency with others that are possible:

    . 916 MHz is available, there's plenty of stuff running there also and Zigbee is able to operate there.

    . 2.4 GHz is available, and used by wireless LAN (including some crazy so'n'sos who run high-power wide-area wireless LAN as a "service"!!), Bluetooth operates there, leaky microwave ovens can emit there, Zigbee operates there as well, and there are loads of continuous sending RF video cameras coming from China that operate there as well.

    Some European regions go part way to solving these problems by imposing duty cycle limits (1% is typical) which helps a lot by getting spectrum hogs out of their band.

    Unfortunately, where regulatory duty cycle limits don't exist them to operate in the unlicensed bands, there is no magic bullet that will solve all problems. We all have to try and interoperate on a non-interference basis - short packets help hugely.

    Cbus wireless has been designed with all this in mind, including the 1% duty cycle limits mentioned above. AND, cbus wireless will always allow control of the locally attached load (provided the input keys and the output channel share the same group), even when communication is not possible.

    Apart from all these precautions, it's up to the purchaser to check their equipment. A degree of finger crossing and good luck also helps.
     
    Last edited by a moderator: Jun 6, 2006
    ashleigh, Jun 6, 2006
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  15. Thomas

    Don

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    Michael, take note that the bandwidth of wireless C-Bus is >20kHz, and "sounds like noise" to an FM receiver with a 25kHz channel spacing (like our 70cm band). The net result is that it doesn't open the mute of most FM receivers used in repeaters (like the good ol' FM828). Try it!
     
    Don, Jun 7, 2006
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  16. Thomas

    MichaelCarey

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    Hi Don,
    You're right, I can't hear it on my radio (which is less than three metres from my C-Bus Wireless gateway), but my radio sure does knock C-Bus Wireless around. Even 1W into a dummy load (433.920MHz) will stop my gateway from receiving.
    My local 70cm repeater gets a work out from the local hire company, they use an industrial strength remote control to control their boom concrete pumps. Whenever they are on a job, the repeater goes mental. On the other hand, I hate to think what transmitting on 433.225 is doing to their system. Hopefully, they have a failsafe installed that stops anything going wrong if the remote link fails.....
     
    MichaelCarey, Jun 7, 2006
    #16
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