AM and Wireless Burglar Alarms?

[Aub]

Sorry if this is in the wrong section, but it does concern Vintage Amateur Radio AM transmissions.

Following a burglary, I thought I ought to install an alarm in the house. A wireless one appeals, because of the simplicity ( so I believe ), but I'm worried about the effect, on it, from my vintage AM Amateur Radio Transmitter. The transmitter knocks my broadband wireless router off the network until I stop transmitting and it recovers. Would it tend to set the alarm off, I wonder?

Does anyone have any experiences, good or bad, with this?

Thanks

Aub.

[Station X]

Quite likely I'd say. My 2 meter transmissions switch on all the security lights within about a 50 metre radius.

Before you think about an alarm you should make sure that you have good physical barriers. Window locks, bolts on the inside of doors and that sort of thing.

An alarm is useless if no one takes any notice of it. Most of the time they don't because there are so many false activations. Remember that the police will not respond to a alarm unless the informant can actually see someone breaking into the premises.

[Aub]

Thanks Graham.

Just wanted something to scare 'em off, should they try and get in again. They already smashed a upvc frame around a door, so i guess it's hard to stop them getting in if they really want to!

My wireless router is in the same room as my transmitter. Perhaps the bell box would be far enough aware not to be effected. Trouble is, I wouldn't be able to switch it off when I go on the air, it being mounted on the gable end, if it is effected.

Oh well....

73's.

[Nickthedentist]

As Graham says, basic things like lights on timeswitches and PIR floodlamps outside are cheap and very effective.

I'd go for a wired system personally, especially in your situation. If you're cunning, wires can be run in cupboards, the loft space, behind curtains, along the picture rail and so on, and also tend to be thin (about 4mm in diameter) so fairly unobtrusive.

Nick.

[ppppenguin]

I'd agree with Nick's advice about going for a wired system. Only use wireless as a last resort. Going even further than that, use door and window contacts wherever possible rather than motion detectors. More reliable and no false alarms.

StationX is right about physical security - make sure that's good, otherwise an alarm is pretty useless. Also make the alarm installation look professional - many burglars can spot an amateur job. Even to the point of doing a logo for the bell box with a plausible name and number of a fictitious security company.

Final thought. If the alarm is set off, then it has failed to do its job. The whole point about both physical security and alarms is to persuade the burglar to look for an easier prospect elsewhere.

[GMB]

Since alarms don't seem to attract much attention, our approach is to put the bells and whistles INSIDE thereby making it uncomfortable for any thief to continue searching (unless they are deaf of course).

The other key thing is to make the system reliable rather than attack-proof like the commercial systems. When we bought our current house we found the alarm system in pieces after desperate attempts by the previous owners to stop it ringing. Every part of it had its own battery backup and if any part saw another part go offline it assumed it was under attack and triggered the alarms. When switched off at the mains one battery eventually ran down triggering a cascade of unstoppable alarms. Quite ridiculous. I notice such systems still exist - a newish one down the road blasts away whenever there is a power cut.

If you want truly low bandwidth logic that is resistant to RF triggering, you can't beat relays

[valveaudio]

What frequencies are you operating your Tx on? Alarm systems operate on various frequencies, earlier ones on VHF, current ones on UHF.
Obvious question is your TX output clean?

Trevor

[Station X]

No matter how clean your transmitter output is it will still cause interference to a poorly designed receiver. The trouble is the owner of the receiver can never understand that fact.

[Paul Stenning]

Originally Posted by ppppenguin

Also make the alarm installation look professional - many burglars can spot an amateur job. Even to the point of doing a logo for the bell box with a plausible name and number of a fictitious security company.

Some security alarm companies will sell dummy bell boxes with their logo on them. Putting one of those somewhere visible high up on the front of the house will probably be more effective than installing a DIY store alarm system.

Remember though that having a visible bell box advertises that you have things worth stealing inside.

[ppppenguin]

Originally Posted by Paul Stenning

Remember though that having a visible bell box advertises that you have things worth stealing inside.

If you live in an area where quite a few people have alarms then it means nothing. Except that if you don't have an alarm your house looks like an easy target. In any case alarms are now fairly common, even in poorer areas so I reckon deterrence outweighs the "something worth stealing" argument.

[Station X]

Just a reminder that anyone, including criminals, can read the posts in these forums. So don't reveal too many details of your own security arrangements.

[M0AFJ, Tim]

How about a very large dog!, mine works very well

Tim M0AFJ

[Trish]

Originally Posted by Station X

No matter how clean your transmitter output is it will still cause interference to a poorly designed receiver.

That is true.. All the same things can be done to reduce or eliminate such problems..

Going back to the OP's original concern.. Starting with the broadband router, and what I would expect to be a case of RF in the shack.. I would check that your matching to the aerial... I would pay particular attention to the RF earthing of any ATU

You don't say what band you transmit on, and what type of aerial you are using.. Long wires that are not balanced (not a dipole) are one of the hardest to tame, as to getting RF in the shack. Which leads to all sorts of problems.. Your router is one, the computer playing up, pickup on an audio amplifier, RF 'bite' from knobs, switches and microphones, are some of the signs of a problem..

Have you tried feeding the transmitter into a dummy load.. If that works and no troubles seen as mentioned above. Then it will be down to the aerial, and RF coming down the outer of the transmitter coax.. That's assuming that your aerial isn't running around your shack that is..

It's always best to start at the source and get that right, rather than try to mask problems further down the line..

Trish (G8DZC)

[Aub]

Thanks for all your replies.

Thinking about this again, I can't remember if I've tried my broadband whilst transmitting, without using the wireless router and going straight from the PC to the ADSL filter. I remember I used to get breakthrough on the phone, before I fitted ferrite cores to the lead between the phone and the phone socket, so perhaps the RF is getting into the phone line and not the router ( although I suspect the router is more prone ) Also, we have the old style telephone wires from poles in the street which, I guess, act as aerials.

I transmit only on one band - 80 Meter AM, usually on 3.615 Mhz. The antenna is a dipole, fed with co-ax to a balun at the centre.

So I need to do a few experiments.

73's

Aub

[Antlong]

Hello all,

I worked for an alarm company for a short while to tide me over after early retirement/redundancy; we had quite a problem with an amateur which was sorted out by fitting better-specified movement detectors, as in all things you often get what you pay for! Certainly a wired alarm would probably be easier to make safe than a wireless setup.

A friend who had problems with his outside lights coming on fitted them with wireless doorbell receivers fitted with a relay to disable them but that seems to me like supping with the Devil, you need a long spoon!

Regards Ant

[Trish]

Have you done any further tests Aub?

By the sounds of it your system should be pretty well balanced.. So you wouldn't have any RF in or near the shack. Which would mean that the RF field would be fairly low near sensitive equipment. Unless of course things are not as they seem with the balancing and you have RF on the coax outer..

With regards to the phone lines that are on the pole. Is your aerial at right angles to the wires, or parallel?

Trish

[Aub]

Trish,

I havent had chance to do any more tests just yet. ( probably be the weekend now ) One half of my dipole is in the back garden and the other half is over the house, but ends about half way along the house. It's actually a shortened dipole, using loading coils, which makes the transmitter think it's a full size dipole. The telephone wires come from a pole across the street, down to the gable end at the front of the house. From there it goes across the roof and comes in at the side of the house. It's hard to say how things are oriented. I suspect the aerial and the phone wires are mostly at 90 degrees to each other. I think I'll try winding some of the phone line round some chunky ferrite cores, but it'll mean disconnecting the line from the main junction box - not something I like to contemplate!

73's Aub

[Aub]

Hi again,

Just to let those interested know, I bought a wireless alarm after all. My AM transmitter doesn't set it off, thank goodness, at least not when it's not armed ( I wouldn't be in the house to transmit if it was armed. ), so all's well with it at the moment.

Still got to sort out the broadband though!

73's

Aub