In response to Bernard Green

[mdf290]

I find it remarkable that you are unaware of interference, professionals are so why are you not?

I wouldn't be able to sleep at night knowing I haven't done my customer a service by telling them the pit falls of these alarms.

How can I not know everytime I post on here Bernard tells me about it again and again and again.

 

[mdf290]

Assume the power of the sensor TX is 10milliwatts. Then assume the jammer has a 1 watt ouput. The jammer is one hundred times more pwerful than the sensor. Square root of 100 is 10 so the jammer can be 10 times further away from the receiver than the sensor is from the receiver to get equal field strength at the receiver. That will corrupt the data from the sensor if the jammer is un-modulated carrier.
Since the jammer attacking a siren can be line of sight free air from the siren and the sensor signal is having to pass through at least one wall losing some of its strength in doing so then a one watt jammer could be 50 yards from a siren and effectively block it receiving any sensor or panel signals.

One watt of ERP can be run from a battery so why are you thinking it would fry the mains.

My response was ir reply to DPT claiming he could jam systems within A MILE radius!! Why did you then do calculations for 50yds and then call me ignorant? really?

Lets do some PROPER assumptions here shall we.
You never even added a value for the distance from the sensor to the siren? lets say its a door contact and it is on the ground floor and its in old money 10 yards from the siren.
Why did you say the sensor output 10Mw?? Thats a ridiculously LOW assumption. The sensors are 4.5v so would usually be outputting around 300Mw...
Lets go with 300Mw shall we to make the calculation more realistic.

So the starting point is a 300Mw TX transmitting 10 yards.
(Ive actually tested the keyfob which is less powerful at only 3v to over 120 yards in open field.)

Lets assume the wall it goes through has reduced its power by 1/3
So we have a 200Mw transmission at 10 yards to beat yes?
I mile is 1760 yards

Now here we have another problem. The Mile radius relates to a house in Gipton Leeds which is NOT open countryside but a sprawling housing area...
So the transmitter will NOT have line of sight to the siren either!!
So lets say it also loses 1/3 of its potential.
To make the calculation easier lets make that the equivalent of transmitting 2346 yards in open sight.

So we have a 200Mw at 10 yards to beat and we are hypothetically 2346 yards away with a jammer. So what output would that jammer need?

The Jammer is 234.6 times further away from the sensor . . so it would need 234.6 x 234.6 the power of the sensor.

Thats 55037.26 x 200Mw just to EQUAL the sensor output.

So what is 55037.26 x 200Mw = 11000 watts Ok so maybe he would not fry the electrics in his house but it would be the equivalent of having five high output devices like irons or kettles all plugged in at the same time.

It certainly wouldn't be a good idea to have plugged straight through one 13amp plug socket. That would have fried that circuit.

So did DPT actually create a jammer that jammed alarms within a mile radius of his home or was he just fancifully imagining things?

 

[bernardgreen]

Why did you say the sensor output 10Mw??

I said 10mW thats is 10 milli watts not Mega watts

The sensors are 4.5v so would usually be outputting around 300Mw

Total rubbish, even 300 mW is wrong. The voltage does NOT determine the effective power of the transmitter.

Untitled

• bernardgreen
• 7 May 2013
• 1

is page 17 from the regulations applicable to SRD radio devices.

http://stakeholders.ofcom.org.uk/bi...-tech-info/interface-requirements/IR_2030.pdf

Note 10mW maximum ERP

So the starting point is a 300Mw TX transmitting 10 yards.

Impossible in legal and compliant equipment.

Once again mdf shows his lack of knowledge of both how radio works and the regulations that apply to the use of radio.

 

[mdf290]

Ok then here is a recalc...

Lets go with 10mW then

So the starting point is a 10mW TX transmitting 10 yards.


Lets assume the wall it goes through has reduced its power by 1/3
So we have a 6mW transmission at 10 yards to beat yes?
I mile is 1760 yards

Now here we have another problem. The Mile radius relates to a house in Gipton Leeds which is NOT open countryside but a sprawling housing area...
So the transmitter will NOT have line of sight to the siren either!!
So lets say it also loses 1/3 of its potential.
To make the calculation easier lets make that the equivalent of transmitting 2346 yards in open sight.

So we have a 6mW at 10 yards to beat and we are hypothetically 2346 yards away with a jammer. So what output would that jammer need?

The Jammer is 234.6 times further away from the sensor . . so it would need 234.6 x 234.6 the power of the sensor.

Thats 55037.26 x 6mW just to EQUAL the sensor output.

So what is 55037.26 x 6mW = 330 watts

 

[bernardgreen]

Sorry but field strength is not measured in watts but in micro-volts per metre or milli-volts per metre.

You say there will be "6 milli-watts" at the siren if one third of the 10 milliwatts from the transmitter is lost in the wall. What if there are two sirens each linked to the same sensor ? (*) will each get 3 milliwatts from the sensor ?

(*) you once admitted that you accidently learnt a sensor into two sirens on different houses that were close to each other. When you tested your install at the second house the siren at the first house reacted as well.

 

[dpt]

MDF, I use 2x 13 element 70cm yagis that are stacked vertically.

http://www.radioaficion.com/HamNews/articles/1480-16-element-dk7zb-70cm-yagi-antenna.html

Since you are an expert on this I will leave it to yo to work out the dbd gain when stacked. The yagi is rated at 15dbd on it's own

I also have them mounted 100ft on a tower.

You may also want to calculate loss

 

[dpt]

Now here we have another problem. The Mile radius relates to a house in Gipton Leeds which is NOT open countryside but a sprawling housing area...

I don't live in Gipton.

 

[cybergibbons]

This thread is full of a lot of opinion.

The 434MHz Yale wireless alarms can easily be jammed without setting off the alarm due to "anti-jam" with about £5 of components. It can be done with a TI Chronos watch.

The power argument... it's pretty simple maths.

The detectors cannot transmit at more than 10mW due to regulatory requirements.

If I use a 500mW transmitter I can be 7 times the distance away from the receiver as the genuine sensor.

If I use a 50W transmitter I can be 70 times the distance away from the receiver as the genuine.

The 50W transmitter doesn't need to be anything fancy as the anti-jam protection is crude. It just needs to do AM OOK at a low frequency.

I don't really have issue with wireless systems, or that they can be jammed. The Yale system however has a number of flaws that are unforgivable, mainly that the code is sent in the clear when using a remote keypad.

 

[JohnD]

Hi Cyber

I love to get to the bottom of these stories.

If you can provide good evidence that an ordinary domestic house in the UK has been burgled by jamming in the way you describe, I will send you £5

If you can provide good evidence that a burglar in the UK has been prosecuted for "going equipped" using a jammer as you describe, I will send you £5

This offer expires 31st May.

 

[cybergibbons]

I've not claimed any of those things, why would I want to prove them?

 

[JohnD]

oh, it's just speculation then?

I wouldn't like people to gain the mistaken impression that the illiterate 15-year olds and crackheads who commit most of the crime (round here certainly, maybe there are white-collar burglars round your way) are using technology to assist them,

Unless it was true, obviously. In which case I am very much in favour of the truth coming out, hence my offer.

IMO it is important to know when we are hearing speculation and when we are hearing real-world facts. For some reason the Alarms forum gets lots of unsubstantiated rumours and there is a chance some people might take them seriously.

 

[cybergibbons]

No, none of it is speculation. I spend my time stopping alarms far more advanced than the Yale ones working.

Claiming that Yale wireless sensors transmit with 300mW and you need 11kW of power to jam them is fiction.

Also claiming that the anti-jam will alarm if the sensors are jammed is garbage. Only the most amateur of jamming attempts trigger the alarm.

There is nothing stopping a £30 device being sold on ebay that would stop Yale and Friedland alarms from working. There is also nothing stopping Yale and Friedland designing alarms that don't suffer from these flaws.

 

[JohnD]

but you don't claim that there are burglars actually using the methods you mention.

So in terms of crime prevention for the average householder, they are just a (not very) interesting topic of conversation.

A bit like the hobby lock-pickers. Irrelevant when the criminal is more likely to kick your door down or lob a brick through the window.

 

[cybergibbons]

In terms of crime prevention, people weren't cloning transponders in car keys 5 years ago. They are now. People weren't removing copy protection on DVDs in 1998, they were in 1999. Locks weren't commonly snapped 10 years ago, they are now. Things change.

Yale and Friedland sell alarms that have 15 year old designs that are easy to jam and bypass for not much less than companies selling much more modern and secure designs.

 

[cybergibbons]

By your argument, people might as well just install dummy bell boxes.