Rf interference. . Any ideas on how to trace the source?

[Ashfaq Juna]

Hello

All of a sudden,  the wireless remote controlled things at home have stopped working or malfunctioning with really reduced range

433 mhz band is affected for sure.

I have a very basic handheld (pic attached ) ’spectrum analyser ’ covering  from  240mhz to 960mhz.  Not much use really as the bands are tedious to sweep through and very narrow.

The display however is jumping around more erratically  than ’usual ’ suggesting that the culprit is a spread spectrum type transmitter.

Any ideas of what to do and how to trace this?

Thank you

[Ashfaq Juna]

[Ryan .]

Maybe start with a quarter-wave antenna for 433 MHz and go for a walk and see what you find? You should be able to find the right length of wire online, you can probably just stuff it in the connector hole. You're doing a crude "transmitted interference" EMC test basically.

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[Ashfaq Juna]

I am currently using a length of wire connected to my spectrum analyser/explorer which came with 433mhz receivers I bought from hoperf a while back,  I am pretty sure that they are 1/4 wave,  I will double check though.

I am not seeing any peaks really,  just erratic readings at various frequencies with values displayed between -110dbm and -105dbm

Are they significant enough to cause jamming like effects?

[Ryan .]

dunno, good way to check your setup is press buttons on a known source at 433 MHz and see what your SNR is. The only place you're really concerned about noise is the receiver, if it's got an antenna, maybe connect that to your analyzer somehow?

[Ashfaq Juna]

Well thing is,  mains switches are affected,  which are self contained and also car keyfobs won't work unless I am very near the cars.

If I press the buttons on  the remote transmitters with the analyser really close. I get readings in the area of around -85dbm

[Ryan .]

Setup's not quite sensitive enough then... Might need some sort of preamp for your thingie to pick up weak signals in the frequency of interest? 

(ps. I'm DEFINITELY not an RF guy, I struggle with this stuff at work. Where's one of the local HAM's?)

[Ashfaq Juna]

Yes,  I agree,  setup is not sensitive enough .. this is a really basic piece of equipment to give you a bit of an idea of there is any rf around you

[Brian Gregory]

Drive and find somewhere away from the interference and compare what you see on your gadget there with what you see at home.

--

Brian Gregory.
bdgr...@gmail.com
www.Brian-Gregory.me.uk

[Ashfaq Juna]

Good idea,

Will do that.

My office is a good Faraday cage.

[Brian Gregory]

Small 434MHz receivers are typically easily desensitised by any strongish signal in within a few 10s of MHz of 434MHz.

It could be something like a tetra base station (police etc.) which transmit a big wide digital signal at, if I remember correctly, around 420MHz.

--

Brian Gregory.
bdgr...@gmail.com
www.Brian-Gregory.me.uk

[Ashfaq Juna]

Or could be they are bugging my house :-) lol

[mikethebee]

My naive thoughts are that a spread-spectrum device is likely to be better managed than a single frequency source such as a cheap remote. I have heard of garage remotes and wireless doorbells getting stuck in transmit mode. The doorbell guy located the source by asking neighbours about new installations and one admitted to having a new doorbell that kept running the batteries down in days, explaining the breaks in interference too.

Mains based comms are also a good source due to the mains wiring acting as an antenna and a conduit to others on the same phase. You can also ask the Radio Agency to assist you in tracking interference. -Mike

[Jim Pugh]

Dunno if its relevant but Maplins are doing these
http://www.maplin.co.uk/bug-sweeper-36653?&C=Email-Newsletter&U=13P5-3&T=scott...@hotmail.com&utm_source=Newsletter&utm_medium=Email&utm_campaign=13P5-3

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Date: Mon, 22 Apr 2013 02:03:43 -0700
From: miketh...@gmail.com
To: reading-...@googlegroups.com
Subject: [RDG-Hack] Re: Rf interference. . Any ideas on how to trace the source?

[Ashfaq Juna]

Thank you all for your inputs.

The problem has gone,  ISM band sockets working OK. So,  I dont really know what the problem was.. not cool. 

I think that I will get the gadget from maplin too.