Hi there,
I got a small job modifying remote relay controllers (recievers) for continuity testing (just adding a transistor, couple of diodes, LED etc..). They use those small generic 433Mhz AM radio modules, along with a small micro for decoding - typical china type thing. (not my design)
Anyways, whilst working on them I noticed, the antenna they use is a helical one - just thin multiicore wire poorly formed into a coil, definitely not tuned, just haphazardly done. But here's the thing, it is completely enclosed inside the aluminum enclosure! There are only mounting holes for LED bezels, XLR connector and a power switch (which admittedly is plastic). The enclosure isn't grounded, or connected to any signal, but is pretty much solid. One thing of interest though is... the dimensions of the enclosure - the long side is 17.5cm.... pretty close to 1/4 wavelength for 433Mhz. Surely it can't use the enclosure itself as an antenna?
There is vast variation in range of these units, I'm surprised they work at all, especially at 30m+. So whilst I have them open, I was thinking of either replacing the antenna with a proper helical one (I don't have the facility to tune them though..) either hand wound, potted, or bought from Farnell, or working out a better way.
I guess the best would be coax from the RF module to an SMA/M4 then to an external ducky antenna, but these units will be thrown around and I fear it will snap off. If external is the only way to guarantee consistency, would a horizontal 1/4 antenna do? enclosed in a plastic box, mounted on the main enclosure? I'm just thinking half the power will be lost as it'll be laying flat, maybe 2-3cm off the enclosure.
Sorry for all the questions, but I'm just surprised it works at all... RF must be getting in there somewhere/somehow. So any idea's, or even just why it works would be appreciated. I'm not much of an RF guy.
Blueteeth
I got a small job modifying remote relay controllers (recievers) for continuity testing (just adding a transistor, couple of diodes, LED etc..). They use those small generic 433Mhz AM radio modules, along with a small micro for decoding - typical china type thing. (not my design)
Anyways, whilst working on them I noticed, the antenna they use is a helical one - just thin multiicore wire poorly formed into a coil, definitely not tuned, just haphazardly done. But here's the thing, it is completely enclosed inside the aluminum enclosure! There are only mounting holes for LED bezels, XLR connector and a power switch (which admittedly is plastic). The enclosure isn't grounded, or connected to any signal, but is pretty much solid. One thing of interest though is... the dimensions of the enclosure - the long side is 17.5cm.... pretty close to 1/4 wavelength for 433Mhz. Surely it can't use the enclosure itself as an antenna?
There is vast variation in range of these units, I'm surprised they work at all, especially at 30m+. So whilst I have them open, I was thinking of either replacing the antenna with a proper helical one (I don't have the facility to tune them though..) either hand wound, potted, or bought from Farnell, or working out a better way.
I guess the best would be coax from the RF module to an SMA/M4 then to an external ducky antenna, but these units will be thrown around and I fear it will snap off. If external is the only way to guarantee consistency, would a horizontal 1/4 antenna do? enclosed in a plastic box, mounted on the main enclosure? I'm just thinking half the power will be lost as it'll be laying flat, maybe 2-3cm off the enclosure.
Sorry for all the questions, but I'm just surprised it works at all... RF must be getting in there somewhere/somehow. So any idea's, or even just why it works would be appreciated. I'm not much of an RF guy.
Blueteeth