Fire Alarm Tripping When I'm On 75M

[W2XR]

Guys,

I recently got back on 75M AM after a nearly 15 year hiatus. The rig (2x 4-400As modulated by a pair of 833As, 130' flat-top fed with 600 ohm open wire feeders) has been all debugged and now seems to be working great. But I'm plagued with severe RFI to the fire/heat sensor to our wired burglar/fire alarm system that is connected to a central office/monitoring location.

A call to ADT (the maker of the system and provider) gave a friendly response, but they offered no technical help. I got permission from them to put ferrite beads on all of the leads (incoming low voltage AC power, motion & fire/smoke sensors, phone line dial-out, etc.) where they terminate within the alarm panel, but this made zero difference to the RFI susceptability to the sensor or the system. I  grounded the panel to earth ground as well.

I think the issue at hand here may be the type of sensor (i.e the technology) that ADT uses for sensing smoke and/or temperature, and it's very high susceptability to RFI. The zone that always trips when I key the xmtr is the smoke/heat detector in the basement. I have put a ferrite toroid right at this sensor (wrapped the lead a few times around the ferrite), but htis makes zero difference in the susceptability of the sensor to the RFI from my rig.

Have any of you had a similar situation? Any suggestions for a cure? I'm going to call ADT on Monday to see if there is a different type of sensor that they can possibly provide that is less susceptable to RFI, and this time I want to speak with their Engineering people instead of the customer service folks in the local office.

This is a royal pain in the butt, as I really want to get back on the air, but every time I do, the local fire department comes to the QTH!! They are getting really p-offed at this point from these false alarms!

Any suggestions would be really welcome.

Thanks & 73,

Bruce, WA2OGS

[kc2ifr]

Bruce,
Your problem could be very tough to solve. Sounds like u did all the correct stuff so far but I have a couple of questions. U say that the zone that trips is the basement device/ zone. Does the led on that device come on and stay on when this happens or does the panel indicate that zone is in alarm but no device (heat/smoke detector) tied to that zone indicates any alarm. If the device itself goes into alarm than it is the device and not the system causing the problem. The other way to trouble shoot would be to remove the device and see what happens. But u just cant take it out of the loop because it is supervised and it will put that zone in trouble. U would have to wire around the missing detector to make the system think it is still there......something that is not difficult to do if you know how. As far as ATD having any answers....good luck.
For now you have to call ADT and tell them to ignore any alarm when u are on the air or shut the system down. Shutting the system down can cause other problems that will piss off ADT!
One more question......how many seperate fire zones do u have on the system?

BTW.....I am assuming your system is a conventional system, not addressable. There is a BIG difference.
Bill

[WA5VGO]

I had a similar problem with our Brinks system. Placing RF chokes on the keypads solved the problem. If that doesn’t work, why don’t you disconnect everything from the controller and reconnect them one at a time until you find the culprit?

73,
Darrell, WA5VGO

[Mike/W8BAC]

I own 3 systems and have installed them in 3 different houses over the past 15 years. They aren't super sophisticated but the main pane supervises the other two and dials out on the Telco line for reporting. The alarm uses the best hard wired sensors available.

I had a lot of problems when I first tried to mix RF with alarms. Darrell has a good point. find the culprit by process of elimination. I finally cured my RFI by using cat 5 cable on EVERYTHING. The cat 5 I use has a foil shield and drain. I ground the shield to the panels which are joined to the utility  ground.

The wire in hard wired systems makes great antennas. My smoke and fire loop is not a simple N/O or N/C circuit so some .01 caps had to be added. The voice coils in the horns could not be tamed so they had to go. Other than that the cat 5 cured the problem. Admittedly, cat 5 is expensive especially with a shield. using only one pair for a lone run is a bit of a waist but it might cure your one or two false alarm circuits.

Good Luck
Mike

[W2XR]

Guys,

Thanks for the insight and suggestions here.

Removing the sensors one at ta time is a good idea in termss of isolating the faulty sensor. This is a supervised system, so you have to be careful how you do something like this, including calling the provider to lift the system from their network so as not to provide a false alarm!.

An interesting point was raised. We have two smoke detectors in the house that are wired into the panel. The one in the basement (which appears to me to be the problematic one, as the message on the keypad indicates this sensor was triggered once the rig is keyed)) does not have an LED indicator on it. But the one upstairs does, and normally this LED will flash brieflty about once every 10 seconds to indicate that the detector is functioning normally. However, last night I noticed the LED was remaining on continously. I don't know if this is due to the RFI issue or not. I think but I'm not sure that these two sensors are wired together within a common loop/zone. The ADT documentation concerning the wiring of my system is poor.

If I can lift each sensor or it's loop off the panel and key the rig and the problem goes away, then I've obviously identified that the fire detectors are the culprit. The next issue becomes what to do about reducing the problematic sensor's susceptability to the RF from the rig.

I can run CAT-5 to the sensor in the basement easily, as the panel is in the basement and all the wiring is exposed and the run length is short. But the upstairs sensor has it's wiring within the wall and that would be a problem.

I wonder if bypassing the fire detector zone at the panel with .001 cpas to ground would be effective compared to the stack of ferrite beads I placed on each of the leads where all othe wiring enters the panel???

I got the funny feeling the sensor itself is the issue. Any idea if these are active or passive transducers? I was told that there are two different types of sensors; photoelectric and ion detection. I have no idea what type we have here, or which type may be more or less susceptable to RFI. My hunch would be the photodetector type, but that's just my guess.

Any further suggestions would be most appreciated!!

Thanks & 73,

Bruce

[KB2WIG]

The ion type usally have a radioactive listing on the sensor/unit body..... the optical ones do not.  For testing or repair, usally a resistor is placed in the circuit loop to give a 'dummy' reading. As far as the alarm co complaining, you are paying them. Let them worry about your satisfaction. You can complain about RF non comliance with the " So, I can't have a garge door opener with your system???" or live near a radio station, fire station,police station, bank , taxi stand.....  Bill, IFRs, sugestions are valid..

One solution is to run the stuff through some emt if you think the cable is picking stuff up. There is signaling cable which may be cheeper than the CAT 5 stuff. Or BX MC types .  Have you tried swaping detectors??  gud luck    klc

[kc2ifr]

Bruce,
If your basement device does not have an LED, then it is probably a heat detector. Heats usually are not affected by rfi.
The device u say usually blinks is a smoke or combination smoke/heat. If u noticed the led on steady......that usually means that the device is in alarm. Can u do a system reset and the led goes back to blink???
Also if the system is in alarm, will the readout or keypad tell u what zone it is or what device it is???
In other words can the system determine if its the basement or the other devices u have?
U might want to call ADT and have them take u off line and then test each device and see what the keypad tells u.
Once u know how the system works.......it will be easier to troubleshoot.

BTW...I install fire alarms for a living. We install commercial systems.....I mean BIG systems. We also install suppression systems and security systems but NOT the residential stuff.

[WA1GFZ]

Don't feel bad I cleared out the Northampton Ma. VA. one day when we mounted an antenna too close to a fire sensor in the attic.

[WA2TTP Steve]

Bruce,

I'm looking at this problem a different way. What about your antenna system? I assume from your post that the transmitter and therefore the 600 ohm open wire feed line is in the same area as the smoke alarm. What if you have some imbalance in the antenna that is causing the feed line to radiate excessive RF into the basement area? It may be easier to convert to a coaxial feed, the 130 length should be a reasonable match to 50-ohm coax, rather than trying to harden the fire system.

Just a thought,

Steve
WA2TTP
 

[W2XR]

Hi Steve,

I thought about that issue re the possible imbalance of the transmission line, and the attendent radiation/RFI issues.

But I have no RFI issues in the basement-located shack or anywhere else in the QTH, and I took great pains to try to ensure that the feedline & antenna system were as electrically balanced as possible, including my use of my homebrew  balanced-balanced antenna tuning unit and best practice physical symmetry throughout the feedline/antenna installation, etc.

Personally, I am not an enthusiast of coax-fed wire antennas, but I can see your point re the minimization of feedline radiation in a correctly set-up coax-fed installation.

I still believe the heat sensor in the basement is the issue. My next test, after reviewing the ADT installation manual last night, is to put the system in the bypass mode for the zone where this sensor is located and key the rig. I will do this before I physically remove this sensor from the loop/zone that it is connected to.

Frank/GFZ: what did you do re the fire sensor issue at the VA? Relocate the antenna???

Thanks for the dialogue, guys!! Any further suggestions are really welcome!!! I'll nail this damn thing yet!!
With Best 73,

Bruce, WA2OGS

[flintstone mop]

Hello Amers
I had a wired ADT system and the dipole was about 20 feet above the roof of the house. All of the wires used for the system ran in the attic and I asked for shielded wire. It cost extra and the system never malfunctioned. The TV did funny things when I was on 75M, but the alarm was perfect. I heard that 75M operation can cause the TV failsafe circuits to malfunction and blow out the HV Horiz output transformer!
Fred

[WA1GFZ]

Bruce,
We moved the antenna outside on the roof away from the sensor. fc

[W2XR]

Guys,

ADT will be here on Friday afternoon, 8/11.

They will be replacing the smoke detector, which I believe is the major culprit here, with a later generation device. They will also be replacing the wiring for the fire detection zone with shielded cable. I'll let the group know how this pans out. I don't know how the later generation smoke detector differs on a technical basis from the unit we currently have installed (1999 vintage), but we'll see.

Thank goodness I have a service contract for our system with ADT. I don't normally take service agreements out on anything, but I'm glad I did this time. They will have to work this issue until it's resolved.

BTW, I have to say that ADT could'nt be more friendlier and eager to please in this situation. Just an FYI; they appear to be very service oriented. Smart business people in a very competitive market. They are also reviewing this RFI matter with their corporate engineering people; this was at my request.

Thanks & 73,

Bruce, WA2OGS

[W2XR]

Hello Fellow AM'ers!

At the risk of being perhaps somewhat premature, I think we may have nailed this smoke detector/RFI issue here at the WA2OGS QTH.

ADT visited on 8/11. At my request, they replaced the smoke detector on the first floor of the QTH with a later generation device that is microprocessor-based. I also had them install a WA2OGS-furnished split ferrite bead  right at the detector, with the wire interconnect wrapped thru the bead several times to maximize it's RF attenuation. They did not replace the interconnect to the panel with shielded cable, at least at this stage of the game.

I then keyed the rig, with the wick turned all of the way up. No false trigger of the fire zone, but the system siren kept making low level beeping sounds whenever the rig was keyed.

I asked the ADT tech to remove the plastic access cover to the solid state siren. I  keyed the rig again and  moved my hand in close proximity to the p.c.b within the siren, and the beeping completely stopped. Reynolds Wrap to the rescue! With the ADT techs permission, I lined the inside of the siren access cover with a layer of aluminum foil to act as an impromptu but effective shield and that did the trick. No more beeping.

I wish I could have kept the smoke detector they removed; I would have liked to see if it was an analog-based device that by design could possibly be more susceptable to RFI/EMI than the new microprocessor-based replacement. The previous smoke detector was 1999 vintage; guys, any thoughts as to the technology employed in this older device made for the residential market that would have made it more RFI susceptable, etc. A friend of mine who used to be in the fire panel/alarm business thought the older units were analog-based with FET circuitry, but I don't know how relaible this information is.

I had the rig on 75M on Friday night for about 2-3 hours, running full strap, and with no false triggering of the fire zone or any other zone. To be safe, I put the entire fire/security system in the test mode while on the air, and for confidence-level testing, I'll probably put it in test a few more times when I fire up the rig, just to ensure that the issue is completely licked.

Thanks for all of the insight and suggestions concerning this matter. Very much appreciated!!!!

73,

Bruce, WA2OGS