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mdf290
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    1. bernardgreen
      bernardgreen
      Using a gain aerial on a transmitter the ERP can be several times the power consumed by the transmitter, From wikipedia to save me typing

      "" Effective radiated power (ERP) is used when calculating station coverage, even for most non-broadcast stations. It is the TPO, minus any attenuation or radiated loss in the line to the antenna, multiplied by the gain (magnification) which the antenna provides toward the horizon. This antenna gain is important, because achieving a desired signal strength without it would result in an enormous electric utility bill for the transmitter, and a prohibitively expensive transmitter. For most large stations in the VHF- and UHF-range, the transmitter power is no more than 20% of the ERP. ""

      For smaller stations the aerial gain can be 20 or more.

    2. bernardgreen
      bernardgreen
      Hi Moving to 866 Mhz is an admission that the 433 Mhz band is problematic. Some of the problems are due to non compliant equipment such as car key fob jammers.

      http://www.newton-security.com/?Product/Product47/CAR-KEY-JAMMER-BLOCKER-315-330-390-433MHZ.html

      which will also kill alarm systems.

      I am not surprised that few reports of jamming have got back to you. Many people are not aware of jamming other than when it is persistant enough for the alarm system to consider it to be intentional jamming and go into alarm mode. Many owners will consider the occasional false alarm as annoying but not a reason to worry about.

      It is a concern that Yale reccomend turning off the jamming detection when there are too many false alarms. But under the licence exempt regulations the alarm system has to tolerate interference from other equipment and still provide a suitable level of service. Other than going into alarm state there is nothing else they can do.
    3. bernardgreen
      bernardgreen
      Hi

      The dis-credited wireless system I was possibly going to pick up has been returned to the supplier as "not fit for purpose" and been accepted as such. There was an attempt to refuse it saying the purchaser should have carried out a survey before purchase. The solicitor over came that by stating that if the supplier considered a survey was necessary then they should have advised the purchaser of that need in writing and as part of the contract to supply.

      Channel occupancy from environmental control devices operating on 433.92 Mhz was around 50% at the threshold of the siren. So about half the signals intended for the siren would have been lost.

      So avoid installing wireless alarms close to large areas of green houses.

      I am waiting for a reply from Yale technical department to some questions posed last week.

      The police concern about jamming in another area has led to a program of sting houses being set up where a wireless bell box is fitted and allowed to false alarm on jamming several times before having the jamming detection dis-abled. Inside the house and securely linked to " various counter measures" is an intelligent jamming detection system. It records precise details about the jamming signal which can then be used to match the signal to the jamming device that created it. Very much like matching a bullet to the gun that fired it. In some sting houses the burglar will be allowed to complete the burglary and be arrested later when the jamming device is in his possesion.


      "" The commercial pressure to sell low cost alarm systems that are so easy to render ineffective is a matter of concern "in high places" and some measures may be put in place to ensure more information is provided to purchasers. ""

      That seems to suggest those who sell wireless systems may have to follow a code of practise when advising customers.

      Bernard
    4. bernardgreen
      bernardgreen
      A door sensor was put in the skip when the door was replaced. The panel gave no indication that a sensor was missing even when the skip was removed from the site. The owner did some tests as to when the sensors transmitted. They didn't unless the motion sensor detected motion or the tamper was operated.

      I found this hard to believe so I phoned Yale technical and the person there confirmed the DIY range only transmitted on motion detect, tamper and low battery. I asked the specific question " If a sensor is unable to transmit or has been taken out of range will the panel detect that the sensor is missing " The answer was no, the panel will not detect that a sensor is missing.

      He then said that only the grade 2 systems using two way communications were able to detect and alarm on a missing sensor.

      A similar reply came from another manufacturer..

      Bernard
    5. bernardgreen
      bernardgreen
      High powered air rifle through letter box aimed at PIR ( yes maybe badly sited ).Sensor wrecked. Glass panel removed, access to hall and panel. Panel smashed No alarm.

      That happened in Boksberg Transvaal South Africa to a house a few doors from a friend's house. She has a fully wired system. Mind you over there gas detectors are quite commonly added to alarm systems as burglars will put a cocktail of chemicals through letter boxes to create sleeping gas to disable and sometimes by accident kill the residents.

      Most wired sensors have self test procedures and will alert the panel immediately they detect a fault. And because power is not restricted these testing and reporting processes can run continuously
    6. bernardgreen
      bernardgreen
      ""kept getting way past 30 and up to 50 activations. maybe they have changed the sensors mechanics""
      How did you detect the activation signal being sent from the sensor. Do you have an off air receiver that can identify the activation signals or was it 30 to 50 flashes of the LED ?
    7. bernardgreen
      bernardgreen
      What effect do you think this

      http://mobile.hama.com/00040936/hama-baby-control-bc-433-mobile

      would have on a Yale wireless alarm.

      Monitoring the audio from the receiver in a wireless linked central heating control system proved that the baby monitor in the next street was the reason the thermostat was not working.

      The "fault" was investigated by a engineer of the central heating manufacturer after 3 thermostats were returned as faulty. He made it very clear that the un-controlled [ meaning licence exempt ] use of the 433 mhz band is causing their customers problems.

      Not saying it was a Hama baby monitor. The recovered audio was typical of a baby in a room with parents. The signal was coming from houses 50 yards away ( using a sniffer with a signal strength meter to determine direction ). It could have been an illegal import.

      The bit that should interest you is that the heating company now feel installers are at risk of legal action if they do not make it clear to customers who request a wire free thermostat or other controller that temperature control cannot be guaranteed when a wireless linked thermostat is fitted.

      Regards

      Bernard
    8. bernardgreen
      bernardgreen
      Hi Mark

      A quick off forum question. When the Yale sensor detects motion it sends one ( or more ) signals to the panel / siren to report activity and then goes to "sleep" for a minute. Yale say that if during sleep the sensor detects motion the sleep period minute timer restarts. This suggests that the sleep will only end when there has been a minute without activity. How does this fit with the panel detecting that it has "lost" a sensor. Does the "I am here" message get sent during a ptolonged period of activity induced sleep ?

      Regards

      Bernard
    9. bernardgreen
      bernardgreen
      A sensor from an alarm was modified to transmit continuously and then thrown into a tree in a residential street. Also modified to be powered by larger batteries to prolong its life as an intentional source of jamming.

      It was realised by some one with a knowledge of radio that the sudden increase in false alarms in the area had to have a common cause and the offending item was located and sent for forensic examination. Whether the criminal was identified and whether any action was taken has not come to light.

      That is not going on the forum as it might give more criminals the idea of how to disable the alarms and allow them to enter houses without being detected.

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