ASK/FSK modules - Is an antenna mandatory?

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I am deciding between the 433MHZ ASk and the RFM12 modules for a wireless application.

I have built the system with the ASK module. I find that event to send data 30cm across, I need an Antenna.

I wanted to know if an antenna is absolutely necessary even with the RFM12 module?

Are there any workarounds?

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Yes, you need antennas to send radio waves (with any form of reliability). That's the whole point. The circuit should be designed so that it emitts close to nothing, channeling every last bit of power through the antenna.
Why wouldn't you want one?

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Quote:
I wanted to know if an antenna is absolutely necessary even with the RFM12 module?

You mean an manufactured antenna??
Because a simple wire + couple circuit could be the antenna. Or there is designs for PCB antennas too.

Regards,

Bruno Muswieck

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I am facing a lot of problems with the ASK module. I am using a 17cm wire whip antenna and yet the communication is unreliable.

Sometimes, if the antenna moves a little the link is broken. That's why I was wondering.

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What you mean wire whip antenna? (sorry, this could be a mistake because of the english).

Does you have the impedance in the antenna that the RFM12 needs?

Regards,

Bruno Muswieck

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@brunomusw:
PCB antenna for MHz range is too big to be practical if only sending data 30cm.
- quarter-wavelength antenna in medium with refractive index n
- n =approx= sqrt() = sqrt(4.25) = 2.06

(c/n) / 477 MHz / 4 is about 10 cm itself. There's some really fancy fractal-based or other designs for microstrip antennas, though.

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Wire whip antenna - monopole antenna. A simple wire and a ground plane.
[Dunno the correct term, but they call it that here :P]

The only way I am able to transmit anything is if I resort to this sort of a contraption:

Uploaded with ImageShack.us

(That's kitchen foil!)

And even then, I am not able to transmit over a meter.

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Do not route the RF across the breadboard with the little red wire. Breadboards are not designed for VHF / UHF RF.

If the transmitter has a pin from the antenna that plugs into the breadboard, then plug your antenna wire into the hole right next to it. Otherwise solder the antenna wire to the antenna pad on the transmitter's board.

You know that the simple transmitter and receiver will require more work in software for reliable communications. Bluetooth & XBee, for example, process the data for you. They send your data within a packet, and will include a checksum or CRC, and will automatically re-transmit the packet if there is an error. With these small, low cost and low power modules, YOU must do all of that.

JC

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Thanks tlucas..

Now I see the problem and the RFM12... And without a oscilloscope as your friend, it'll be hard... The oscilloscope you'll be able to start to see something...

Regards,

Bruno Muswieck

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If you are able to achieve (albeit unreliable) communication across 10cm, there's no reason it wouldn't work across larger distances given proper layout and antenna. Breadboards are probably the absolute worst medium you could possibly use to design a RF circuit. A lot of them have capacitance in the pF range at each crossbars.

I would say put what you have on a proper PCB, home made or not, and see where you go from there. I can only recommend you follow the recommended layout guidelines in the module's datasheet closely. As for the antenna, look for a bent monopole PCB antenna, I have used it with some success to distances > 30m on the 915MHz band.

Alternatively, it seems in the 433MHz range you can get away with a simple ISM ceramic antenna like this one:

http://www.simplesolutions-uk.co...

Costs about a dollar each.

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Thanks for the replies.

I will prototype on a dot PCB and try one of the antenna you guys have suggested.

PS: This thread is proof again that a picture speaks a thousand words!

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My updated antenna (After reading a little on antenna theory)

Works a little better

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Hi shaunak i have also experienced problems with whip antenna. Better option is to use a small helical antenna and never try to route the antenna pin through breadboard.

-Krishna Balan S

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