Security alarm extension speaker hearing my HF SSB signal

Discussion in 'EMC Matters' started by Philip Catterall, Jan 1, 2019.

  1. Philip Catterall

    Philip Catterall New Member


    Before I start to delve into this minor issue with my excellent next door neighbour, I thought I would see if anyone on the EMC Forum has come across a similar problem and found a quick fix for it.

    My voice has been heard on my neighbours burglar alarm extension speaker. The speaker is 21 years old - I do not believe it has any built in amplification, and it has no tamper switches as this is the budget model.

    This is the Kinetic KSB5516 Mylar extension speaker - pdf attached. I need to conduct some testing with my neighbour, arrangements have been made for testing next Saturday morning. The issue arose when I was running 150 watts output on SSB on the 20m band to a Hexbeam at 13m AGL. My antenna is around 15 metres or so from the loft mounted alarm box

    The alarm remote keypad is in the hall of the detached house next door to mine. The speaker is above a doorway in the same hall. The remote alarm box itself (without controls) is in the loft of the house and is easily accessible. The neighbour is cooperative. All the extension speaker does is confirm the tones as you enter them on the keypad. It then emits the warble when the alarm is set prior to locking the front door. I imagine it will also sound if the alarm is activated.

    I have ordered a replacement identically numbered CE marked extension speaker anyway - less than £7 including postage, so I can use that for any modifications prior to installing it as a direct replacement.

    I believe unless anyone knows anything different my start point will be to get inside the replacement loudspeaker I am buying and install a ferrite choke in the feed to it. Is there anything else members think my be worth trying, including at the alarm box end in the boarded out loft space of the neighbours house.

    73 and a Happy New Year

    Phil G4OBK

    Attached Files:

  2. Ken G3SDW

    Ken G3SDW Moderator

    Hi Phil, happy new year to you and yours from the EMCC.

    From first impressions with your details then the new extension speaker, which would appear to be powered with 12 volts, then by winding as many turns around a good quality grade ferrite wring, type Fair-Rite 43 material, then you should be able to cure it stone dead.

    From your description then there appears to be a rather long run from the loft to the speaker unit so it is understandable why this is happening and assuming the extension speaker that is there now then it must have a few years under its belt.

    Let me know how you get on but dont think you will have any further problem.
    Philip Catterall likes this.
  3. Philip Catterall

    Philip Catterall New Member

    Hello Ken

    Thank you very much for your thoughts. I have some unknown ferrite rings here but I will try to source a few in Fair-Rite 43 material, one to use and one for stock. I know about the G3TXQ webpage relating to ferrite material so I will review that. (Recent SK - a real expert in many areas who shared his knowledge widely - he will be missed).

    I'll let you know how I get on...

    73 and HNY

  4. Ken G3SDW

    Ken G3SDW Moderator

    Hi mate yes I also heard about G3TXQ a sad loss to our great hobby.

    You can get some 43 type rings from the RSGB shop online, that way you will know you have the correct ones, sadly many amateurs just use any old ferrite and do not appreciate that the grade is very important.

    As I said use a ferrite ring and replace the speaker and think anyone would agree that it must do the trick.

    Ken G3SDW
  5. Philip Catterall

    Philip Catterall New Member

    A good tip about the RSGB shop Ken, thanks. I never realised.

    All the best

  6. Philip Catterall

    Philip Catterall New Member

    Hello again Ken / whoever else is reading this. Eventually the 43 rings arrived from HQ - They probably had a holiday shut down for Xmas / New Year.

    A new speaker was obtained of exactly the same type as the one fitted in 1997. Very cheap - £7 including postage. I wound a choke and have fitted this today in line at the loudspeaker in the hallway. The speaker is passive - the 12V referred to should read 12W (Watts!). Fitting the choke has resulted in a partial cure - I think the audio / CW breakthrough is now around 50% what it was before, however it is still there if I run the full 200 watts from the FT5K on 14 MHz. Worse case scenario - with my Hexbeam pointing directly in the direction for maximum gain.

    Do you think the RF is being detected and then demodulated within the control box in the loft and then fed to the speaker? Plainly some is getting through the tightly wound choke. All the speaker does is confirm by tones that the alarm is being set when the digits are entered into the remote keypad in the hallway. It would also no doubt sound if the alarm was triggered.

    Would fitting what is known as a soundbomb instead of the standard mylar cone speaker with magnet be likely to help completely resolve the issue? I'm not sure what a soundbomb actually is... maybe it is just a small speaker with a diaphram, the same in effect as what is in use.

    Any thoughts on what I try next? The neighbour is very cooperative - there would be no problem in going into the loft, pre-winding another 43 choke with standard 6 way alarm cable and then fitting that in line inside the alarm control box at the control box end of the lead going to the monitor speaker. Do you think this is likely to help cure the breakthrough 100% or like most of these cases suck it and see?

    Phil G4OBK
  7. Ken G3SDW

    Ken G3SDW Moderator

    So Phil as i see it then the speaker is just a speaker connected to some sort of audio amp which from your description must be in the loft space.

    So now you need to explore were it is getting in, for sure its not on the output as this is were the choke is now.

    So take a look at the input which again from what you say must be in the control box, is that powered internally or has it an external power source as it could be getting in either.

    That`s were you need to be looking now Phil.

    How old is all of this as from what you say it being in the loft then it has been getting damp for a time due to changes in temperature, summer and winter, which creates moisture, plus caps dry out.

    Just some thoughts about your latest description.

    Keep in touch, as i am always here.
  8. Philip Catterall

    Philip Catterall New Member

    OK Ken, thanks for your thoughts.

    The house was built in 1996, alarm fitted in 1997. No dampness in the loft. As a favour I put a new SLAB lead acid battery in the control box about 6 months ago. The old one was the original dated 1997 and it was kaput. So if there was a mains failure or the main circuit breaker tripped, as it did 6 months ago the alarm would sound as the battery due to its age, could not supply current to make up for the loss of the mains.

    Its a long story but we lived here from 1997-2000 and then sold the house, and then we bought it back in Nov 2016 after the older couple we sold it to died. This EMC alarm issue mentioned once when we lived here before, in 1998, but I did nothing about it then, so the issue in not down to age or the system or deterioration of it.

    So here we have a mains powered control unit (with 12V DC battery back up in the event of a mains failure) installed in the loft of a two storey house. The board must have an audio amp built into it to provide tones to the loudspeaker in the hallway, which is also where the remote keypad is for the alarm system. The system has the usual wired PIRs for detection and reed switches on the front and back doors for detecting access / exit. That's it.

    73 Phil
  9. Martin G0HDB

    Martin G0HDB New Member

    Hi Phil, if the mains-powered control unit for the alarm system has sufficient slack in the mains cable feeding it, or if you could extend the mains cable, then it would be worth fitting a large clamp-on ferrite core onto the cable to see if that helps - your RF might be getting into the audio amp inside the control unit via the mains. Alternatively, it might be worth trying a clamp-on core on one or more of the connecting leads that go from the control unit to the sensors (and to the remote keypad?).

    The recommended core for such uses is the 'Big 31 Problem Solver' as shown on Ian GM3SEK's website at:

    As indicated, it'll need several turns of the mains cable to be fed through the clamp-on core for it to be effective.

    Although these big #31 cores aren't cheap (around £15 each when I last bought some a few months ago), if you order a few from Mouser there'll be no carriage to pay and they'll arrive quite rapidly from the USA via FedEx. I regard them as money well spent because they really do help to cure some significant RFI problems - I only wish my neighbours, who have some very noisy apparatus, were as co-operative as yours when it comes to sorting out RFI problems... :-(

    Martin G0HDB
  10. gm3sek

    gm3sek New Member

    I still recommend those large clamp-on cores very highly indeed. Nothing beats them for a "quick fix" (and also for finding out which cables actually don't need a choke).

    At least one club has combined to make a bulk order from Mouser. It only needs 4 or more cores to qualify for the free Fedex delivery, which is fantastic - delivered to your door in 3 days, which is fastr than many UK suppliers, and nothing extra to pay. By all means compare prices from different suppliers, but when you include all the costs, Mouser will still come very near the top.

    At first I felt quite concerned to hear that a club had commited a large amount of money, just on my say-so... but all the feedback indicates that if common-mode current is your problem (remembering that sometimes it isn't) then these cores will almost certainly help. When people say "Thank you so much - I've got my hobby back," that makes it all worthwhile and I know Ken feels the same.

    73 from Ian GM3SEK
  11. Ken G3SDW

    Ken G3SDW Moderator

    Thanks for coming in both of you, its a great help.
  12. Philip Catterall

    Philip Catterall New Member

    Thanks Martin and Ian for the info regarding the large ferrites available from Mouser. What a ferrite!

    A single big 31 core with the £12 postage will cost £26, two will cost £40. I'll likely order two and keep one back as a spare. I want to have a look at the control box first and having reduced the audio by 50% with the 43 ring at the speaker end I will likely put one of the 43 rings on the output line from the control unit going to the extension speaker first. Standard 6 way alarm cable is used with only two cores going to the speaker. I cannot tell if the other 4 cores are in use for another function as other alarm cables are terminating in a choc block inside the speaker housing which are are then routed out elsewhere.
  13. Ken G3SDW

    Ken G3SDW Moderator

    Hi Phil think what you have said is the right way to go.
    You said before that this unit has battery back Up, you could try taking out the mains supply to get it running on battery supply and this way will eliminate whether or not the RF is getting onto the unit via the mains power supply.

    Just a thought.
  14. Philip Catterall

    Philip Catterall New Member

    That's a good point Ken. Worth physically isolating the mains from the unit in that case and allowing it to run from auxiliary battery supply in the unit. I imagine there is a fused switch near the unit. Further investigation needed next week. Watch this space.

    73 Phil
  15. Ken G3SDW

    Ken G3SDW Moderator

    One other thing that you said about the loft not beingbe damp well just think about it as it's the only place in the house that has extremes of temperature and this sets up moisture so lofts are far from dry.
    Good luck and look forward to some good results.
  16. Philip Catterall

    Philip Catterall New Member

    Dear Ken / All - reporting back

    Even with the mains supply isolated the audio was still breaking through the loudspeaker at full legal limit and could be heard standing in the hallway.
    I fitted another 43 ferrite ring wound with 6 way alarm cable, utilising just the two conductors for the speaker and put this in series at the control box end in the loft. Not completely cured but virtually - certainly on 14 MHz. To hear anything at full legal limit I have to put my ear right next to the extension speaker. My 82 year old next door neighbour was so pleased she plied me with fruit cake and tea once the job was done and gave me a packet of luxury biscuits to take home.

    Wouldn't it be great if all our neighbours took on board EMC issues in this way?! I told she shouldn't, but she insisted on giving me the biscuits. Having said that I did retune her bedroom TV which wasn't receiving any channels, so she was great grateful for that.

    There is another issue - and I am 90% it is her boiler affecting me!!

    Has anyone come across a Vaillant ecotec plus 418 gas fired central heating boiler that emits a hetrodyne every 16 KHz (approx) from 10 MHz right through to 20 MHz? While I was in the house I DF'd the hetrodyne I hear every day in my shack, using my KX2 and I am 90% certain it is the boiler. The hetrodyne comes on throughout the day for short or long periods. More investigation is needed and my neighbour is happy for me to go back and check again when we both have some free time.

    I'll let sleeping dogs lie for a while, the issue has been there since I went on air from here in January 2017. The hetrodyne is S8 if I point the Hexbeam in the right direction, using FTDX5000 with no preamp in circuit and S9 + 15 db with Preamp 2 switched in.

    BY the way I have ordered 3 of the Big 31 ferrite split chokes today from Mouser and got the free postage. I'll keep two - and will fit one to my own station and keep a spare and sel on the 3rd. Ordering 3 once the VAT went on I achieved the Fedex free postage.

    Thanks for the tip guys and 73 to all readers

    Phil G4OBK
  17. Ken G3SDW

    Ken G3SDW Moderator

    Hi Phil well great news.

    And as long as your neighbour us happy then that's everything and yes it is so nice to hear about cooperative ones they are half the battle as once they slam the door in your face then we have lost the fight as there us no one that came force them to do So, sad world we live in.

    As for the boiler then most complaints I get are from that make and the problems come in all sorts of different symptoms.

    I think to start with you may well like to try one of those 31 type ferrite on the mains cable, as many turns as possible so you may have to make it with some extra cable assuming that the cable is there will be on the short side.

    As they say suck it and see.
    Let us know how things go and enjoy your biscuits, what a nice gesture, old school I see lol

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