Scantronic 500r+ RF Trouble

[rwiddowson]

Hello again,

For years I have had the above alarm system installed.

An electrical contractor friend did the wiring to the mains panel and I did all the fixing of the wiring switches.

It has given nothing but trouble in terms of RF Trouble. I read on the internet somewhere that all that is required is to change the anti-jam jumper to OFF?

Some clarity on this would be greatly appreciated. I have been suspecting for some while that taxis and the like (perhaps Police cars using their radios as they pass) had been causing the triggers.

Funnily enough, I do not remember one time where it was ever triggered when we were in bed. It always seemed to used to trigger within 30 minutes of setting or so or when we were overseas.

If anyone can shed light on what this jamming feature should do when it is ON and OFF that would be fantastic.

Also, just changed a few wireless PIR batteries. They are the Scantronic 520R wireless PIR's.

When I removed the covers, it caused the tamper alarm to go off on 2 out of 3 occasions.

Batteries were down at 1.15V on 2 which triggered and down to 0.6V on the one that didn't trigger the anti-tamper.

Can someone explain why they would even go off if they were below 1.5V and not lighting when someone walks in front of them?

Cheers in anticipation.

 

[bernardgreen]

If anyone can shed light on what this jamming feature should do when it is ON and OFF that would be fantastic.

Jamming or blocking is when a radio signal prevents messages being received by the item that should be receiving them.

In a wireless alarm system jamming has almost the same result as cutting the wires in a wired system. In a wired system the tamper detection will report the cut wire and trigger an alarm.

In a wireless system jamming has to be treated as a tamper because a common way to defeat a wireless system is to jam the radio channel thus preventing the control panel amd/or siren receiving alarm message from sensors.

False alarms occur because many alarms use a licence exempt frequency for the radio communications, the most common being 433.92 Hhz. This is also used by among other uses baby monitors, car key fobs, wireless lighting and heating controls, the list is long. Signal from these will be received by the control panel abd/or siren of nearby alarm systems but as they will not have a recognised identity they will not been seen as alarms. They will block or corrupt any alarm messages sent at the same time.

The alarm system has to ( as a condition of the licence exempt use of the radio channel ) tolerate and operate properly in the presence of jamming signals. So if it sees a tamper condition it goes into alarm.

If you have too many alarms due to jamming and turn off the jamming detection you will not know if your alarm has been ( or is being ) blocked. If it is blocked at the time there is a break in the messages from the sensors will not be received by the panel and/or siren and no alarm will happen.

 

[bernardgreen]

Sensors with low batteries do not send "Tamper" instead they send "Low battery" provided there is enough power left to be able to transmit. If the battery is too low the sensor cannot transmit.

If battery goes so low that the sensor cannot transmit "low battery" then the panel is un-aware that the sensor is no longer working. Some but not all alarm systems are not able to realise that one of their sensors has died and assume that as the sensor is not sending "alarm", "tamper" or "low battery" messages then all is OK with the sensor. Doing frequent walk tests is essential with this type of system to ensure all sensors are still active.

 

[EightyTwo]

Scantronic recommend that the alkaline batteries are changed every year. They do not guarantee that they will last more than 14 months.

They also recommend that the cntrol panel is installed at least a metre away from other cables.

If you have really had your 500r+ for many years, it might be operating on the old frequency (415MHz, I think) which was sold off by the government for TETRA (I believe - bernardgreen will put me right!). This could cause 'trouble'...

Finally, remember that the PIRs 'sleep' for 3 minutes after being triggered.

 

[bernardgreen]

I cannot recall whether 415 Mhz was ever available for alarm systems though I have a vague memory of it being used for telemetry.

415 Mhz was re-assigned in 2006 after Dolphin ceased operation in 2004

Used as one of a TX RX pair for PMR / TETRA

http://stakeholders.ofcom.org.uk/consultations/spectrum_award/statement/


It might have been 418 Mhz

 

[rwiddowson]

418MHz it is.

What does this mean in real terms?

The JAMMING jumper I moved the other day was to the OFF position.

I cannot recall EVER touching that.

So with jamming ON (as it was) would this have been the possible cause of the false alarms?

Go to say I am not a fan of wireless alarms and would much prefer a hard wired solution.

 

[Europlex]

Note the frequency.

The radio operating frequency between the control unit receiver and the detectors is 433.92MHz with a bandwidth of 200kHz.
The radio section is approved to MPT 1340 and ETSI 300 220.

Before installing a 500r+ system make sure you are fully familiar with the functions of the control unit and the various system plans and detectors described in this manual.

 

[bernardgreen]

So with jamming ON (as it was) would this have been the possible cause of the false alarms?

Very likely it was. With a wireless connected alarm jamming is the same as cutting all the cables. So the only way the system can inform the owner of this tampering is to sound the alarm. Jamming can be "accidental" or deliberate. Deliberate jamming is often part of a criminal action to dis-able or dis-credit the alarm so the user does not use it any more. With jamming detection OFF the system can be rendered in-operative by a simple, easy to purchase, jamming device.

Go to say I am not a fan of wireless alarms and would much prefer a hard wired solution.

There are many places where wireless is the best option but almost all such cases involve an item that is mobile and cannot be wired. In these cases a two way communication is almost always used and the radio frequency might not be a licence exempt one.

 

[rwiddowson]

So basically I need to move the jumpers back to Jamming ON from what you are saying?

 

[rwiddowson]

Perhaps I should have been clearer.

To ensure greater security, should I change it back to what it was when it was giving me RF Trouble and try to diagnose what is causing it?

I am pretty sure it is 418 MHz but someone said it is 433MHz which car key fobs seem to use. I know that they have a specific ID which should prevent anything else communicating with it and setting it off.

Perhaps I should do a Walk Test with it set as it is because I am pretty sure that the PIR's are still communicating with the panel