Question for Antenna Heads!

deandean

Not quite amateur radio, but I am hoping you'd have some ideas:

So I have a wireless shock sensor for my intruder alarm that's right on the limit, distance-wise. Once every week or two the system 'loses' it.

The sensor transmits at 868MHz. The antenna in soldered to the PCB, it's shaped in the form of a spring with a straight bit, I guess its tuned to the tramsmit frequency. Photo below.

What can I do to improve the transmission distance by about 10%?

Is there any point in attaching a longer wire to the end of the antenna. Or could I de-solder the antenna from the PCB, mount it somewhere more favourable & connect to the PCB with a piece of wire?

Any ideas welcome!

Many thanks.

martinsvi

putting a wire on top of it will de-tune it, it will introduce a standing wave that will attenuate the signal. Similar thing will happen if you de-soldier it and move it - you will have great difficulty matching it's impedance I think, also any cable will introduce losses. I'd say - don't touch it and try to solve your problem by decreasing the distance between two "stations"

watty

It's illegal to change the aerial as that is part of the certification.
See SRD 868MHz regulations on www.comreg.ie

Wireless alarm systems are toys. They are inherently insecure. Use a cabled shock sensor to a real alarm system.

I'm not going to explain how, but I can trivially make your system useless with cheap readily available gear.

brownmini

deandean wrote: »

Not quite amateur radio, but I am hoping you'd have some ideas:

So I have a wireless shock sensor for my intruder alarm that's right on the limit, distance-wise. Once every week or two the system 'loses' it.

The sensor transmits at 868MHz. The antenna in soldered to the PCB, it's shaped in the form of a spring with a straight bit, I guess its tuned to the tramsmit frequency. Photo below.

What can I do to improve the transmission distance by about 10%?

Is there any point in attaching a longer wire to the end of the antenna. Or could I de-solder the antenna from the PCB, mount it somewhere more favourable & connect to the PCB with a piece of wire?

Any ideas welcome!

Many thanks.

I have an idea which might require surgery to it but I'll keep that off the table for now.

Long shot 1.
If the orientation of the actual module is not critical then turn it around 180degrees so that the aerial wire is 'pointing up'.

Long shot 2.
If the orientation of the actual module is not critical then turn it so that the aerial is side on to the intended reception point.



If you look carefully, you see that the little circuit board with the aerial on it has a small chip and other stuff on the other side from the coiled up aerial.
This is your 868MHZ module and it looks like its soldered onto the main board using those three long links-pins.

You probably know that a 1/4 wavelength at 868MHZ is 8.6cms.

deandean

thanks brownmini, your mention of surgery has given me an idea,you might be thinking the same thing?
the three connections to the RF board seem to be 0V, +ve and data. the board itself might be acting as a very small ground plane. So, unzolder the RF board, extend the three conductors by a couple feet and mount the RF board in a more favorable position?

watty

Pointless

1) It's crap and easily defeated

2) Any modification makes it illegal to operate!

brownmini

deandean wrote: »

thanks brownmini, your mention of surgery has given me an idea,you might be thinking the same thing?
the three connections to the RF board seem to be 0V, +ve and ....

My idea (the secret 3rd one) would have left your module completely intact and looking the same but with one addition.

Just a thought, you say you need an extra few feet or so on the range of the module (I presume to get to the main unit).
Is there any way you could improve the reception ability at the main unit rather than perform surgery on the module itself?

martinedwards

pro burglars will have a jammer in their bag.

just like the shoplifters now invest in £30 Baofengs to listen into the shop security radios.

I'm with Watty on this.

bin it an buy some cable.