Fairly modern house alarm "bell" boxes. What's in them? RF issues. - Page 1
Forum section: electronics / general

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 12, 2017, 07:49:56 pm
content: I am getting RF from my LF transmissions making the house outside alarm create short, intermii=ttent yelping sounds. I am planning a strategy of isolating if RF is getting into the cable from the control panel to the sounder box, or into the sounder itself. The yelps occur with the alarm in "Day" mode, so i don't think RF getting is into the sensors (reed door open switches and break glass detectos (no PIR's are fitted), or the control panel itself.The sounder was fitted by myself in 2006 replacing a duff one. I can't recall if it just had a battery and a mechanical relay in it, or if it had semiconductors. Any thoughts on isolating the problem please?I have laid out a length of 8 core screened cable alongside the original none screened six core panel to sounder cable, and will probably replace it, with the screen grounded at the panel end. If push comes to shove, being 8 core would allow me to have the option, I hope, of having a relay at the panel nd that only connects the sounder when nthe alarm is in the set (alarmed) mode?Thanks.

author: Gregg
author_rank: Super Contributor
timestamp: November 12, 2017, 09:29:31 pm
content: We need more information in order to provide much help.1. What brand and model is the panel2. Brand and model of the siren or whatever is making the intermittent sound3. Can you make it sound by turning on whatever you are assuming is the source of the RF?Some alarm panels have a dubious feature that omits a squawk when it detects a battery problem (some smoke detectors do the same).Most sounders require a little more than induced RF to make a sound. Try disconnecting the bell and put a LED (with an appropriate dropping resistor) across the bell outputs at the panel to see if voltage is originating at the panel.I would bet on a bad connection and/or a failing capacitor somewhere.

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 12, 2017, 09:39:07 pm
content: Panel is an Optima XM6. Bell box is a Pyronix Belle. Definitely RF, I fire up a 1kW amp into a very electrically short antenna and it starts intermittent chirps. Battery in panel and bell box are both good.100% sure it's an RF problem, if I reduce TX power it doesn't do it. But as to where the RF is getting IN to the alarm....? Thanks for the speedy reply!

author: Gregg
author_rank: Super Contributor
timestamp: November 13, 2017, 01:18:12 am
content: Since I have never personally worked on an Optima alarm panel; I don’t have any specifics; but I’ll try to add some general ideas.By my Google searches, it looks like the alarm is an all in one alarm with keypad, alarm panel and battery all together. It appears the case is plastic and that the mains power terminates inside the case.You might try disconnecting the mains and running the alarm from the battery for a test. If you can, disconnect the mains wire as far from the panel as possible.The zones appear to be normally closed which in alarm-language means they are closed when not in alarm condition. End of line resistors are not apparent. You might try disconnecting the loops one at a time and shorting the zone at the panel at the same time shorting out both leads of the zone to ground to minimize any antenna effect. A poor connection at a reed switch may become a semiconductor, not likely but possible. If a number of sensors are daisy chained in series on any zone, troubleshooting becomes much harder.As you are probably aware, plastic cases don’t restrict EMF. Something like a poor solder joint could be the problem. If a battery has ever leaked, a good cleaning and inspection of the board both sides may be in order; acid fumes can go anywhere.My searches on Pyronix Belle are lacking in details. It seems that the alarm installers where you are want to keep everything secret. We should try to change that attitude.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: November 14, 2017, 08:17:19 pm
content: First thing I'd try is putting a large ferrite on the cable near the box. If that solves the problem, saves opening it.

author: Muttley Snickers
author_rank: Unknown
timestamp: November 14, 2017, 09:36:35 pm
content: I'm not familiar with either your control panel or the external siren and only had a quick look at the Optima XM6 installers manual, if it is a 12 volt hard wired external siren then I would suspect that the output is bleeding, the DSC panels had a reputation for doing this as well unless a 1k resistor was fitted across the output, this was also required for siren/ bell tamper monitoring. The RF interference you mentioned earlier does sound a bit strange and not a scenario I've ever encountered in relation to momentarily triggering the control panel outputs.It also looks like the Optima XM6 incorporates an additional horn speaker output which depending on the configuration may activate or chirp for the arming and disarming sequence, I don't know which output is the problematic one but suspect the first, I found a stack of wiring diagrams for the Pyronix Belle external siren housing but will need to take a closer look at these from the computer which I'm not currently on. You also need to confirm whether or not this is a satellite siren in which case there will be a backup battery onboard which is probably dying.

author: Chris Wilson
author_rank: Super Contributor
timestamp: November 15, 2017, 12:22:49 pm
content: Update:Fitting the big clamp on ferrite from my TS-590 transceiver power supply cable (original Kenwood ferrite, but the transceiver is not used for low frequency TX), to the sounder box multi core cable, right up where it goes through the outside wall to the sounder box made no noticeable difference. But if I power the alrm panel down entirely, with no mains input and the panel;'s internal battery disconnected, the outside sounder box does NOT chirp. I guess RF is getting into the panel itself then? The odd thing is when the outside box chirps the panel does not go into a tripped circuit alarm mode, it just sits there as if nothing is triggering it. One option is power it down when transmitting. I have also found that just running the panel on its internal back up battery also causes the sounder to chirp... Thanks for the replies, any further insight very welcome!