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Fire alarm RF interference susceptibility

Discussion in 'Radio and Wireless' started by dgaines, Nov 4, 2011.

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  1. dgaines

    dgaines

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    Nov 4, 2011
    does anyone know if a 72mH RF signal can trigger hardwired solenoids on a fire alarm system damper control?
     
    Last edited: Nov 4, 2011
  2. davenn

    davenn Moderator

    13,598
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    Sep 5, 2009
    hi there
    welcome to the forums :)

    I assume you mean 72 MHz ?
    It would depend on the power of the 72MHz transmitter, its proximity to the fire control equip and the design of that equip and how resilient it is to any sort of RF signal.
    Without knowing any of those things and being able to do some testing. It is pretty much impossible to give a qualified answer

    cheers
    Dave
     
  3. dgaines

    dgaines

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    Nov 4, 2011
    Dave,

    I am working with a 5 watt wireless clock transmitter operating at 72MHz. It is located on the 6th floor of a new facility currently under construction. The 6th floor is a mechanical room for the entire facility. There is also a level below grade. The antenna for the transmitter is located on the roof of the building approximately 50 ft from the transmitter. There is also a GPS unit to synch the transmitter to a sattelite. I believe the fire control panel is located on the 4th floor directly below my transmitter and will verify Monday A.M. I have been told that when our system is in operation, smoke control dampers that are operated by hard wired solenoids close without cause. This is not a facility wide issue but seems to only effect some dampers on the 6th floor and the below grade level. I have also been told that since our tranmitter was turned off the issue has ceased. I have spoken with the manufacturers tech who installed the transmitter and there senior tech advisor as well as other integrators who sell and install both systems and none have ever seen this occur. Any insight is greatly appreciated!!
     
    Last edited: Nov 7, 2011
  4. jackorocko

    jackorocko

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    Apr 4, 2010
    out of curiosity have you turned the transmitter back on without anyone knowing it to verify the issue still persist. Some always try to find fault whether it exist or not. Could have just been a big coincidence though unlikely.
     
  5. davenn

    davenn Moderator

    13,598
    1,875
    Sep 5, 2009
    hi dgaines,

    well if the transmitter is housed in a usual metal case and the coax cable going off to the antenna is ok then the radiated RF from the transmitter and coax will be negligible. 99% of the RF will be transmitted from the antenna and as you said its quite some distance away. over 50ft of coax, with 5W going in, there's (without doing the exact attenuation calc's) probably only ~ 2.5 - 3W at the antenna anyway.

    Thats a pretty low power level. Have you a mate in the radio electronics trade that has a spectrum analyser ? (if I lived near you I would pop around with mine) that would conclusively tell you what sort of RF levels were present in the room with fire control gear. There is the possibility there is some RF being picked up by the fire control cabling from throughout the building. BUT flamin' heck if they were having probs with a 3 Watt radiating antenna >50ft away then the systen is going to totally fall over with every security guy and other bloke with a 3W handheld radio rigtht up close and personal with the gear!!!
    As jackoroko said.... I would almost be tempted to switch back on without anyone knowing and see what happens ... specially now whilst things are under construction .

    cheers
    Dave
     
  6. dgaines

    dgaines

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    Nov 4, 2011
    Dave & Jackoroko,

    Your suggestions are invaluable. I am going to slide up to the site this morning and turn on our tranmitter and check to see who has hand held radios on the site. The fire alarm vendor has tech folks there today to evaluate the problem. We do have a retired NASA engineer at our corporate office who is an RF guru and will have him come down and run a spectrum test if everyone keeps pointing the finger at me.
     
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