433 MHz transmitter range bad. Measure and improve


First of all, im having some trouble with my 433Mhz transmitter and receiver module. Their range, is rather bad. Its reliable at around 8 meters but further than that i get unreliable results. Furthermore the 433Mhz module is to be placed inside a mailbox which is all out of metal, and i suppose this makes the transmitter even more unreliable.

I’ve tried with some normal wire as an antenna, which helped a little somewhat, but not enough for it to work as i had hoped.

Is there something i need to do ? Can i somehow boost the transmission performance?

Use better transmitters and receivers, some transmitters are only for 3.3V or 5V. The transmitters that are 3 to 12V have only maximum power at 12V. I use those cheap 3-12V transmitters, and have no problem with 3V and 30 meters range. I don’t use the cheap receivers that are tuned with a coil, I use those with a crystal.

The antenna should be a wire of 17cm. But I had trouble receiving certain transmitters. I use now a wire of 1.20 meters and that is better. Perhaps the antenna impedance is lower with a longer wire.
Just a small test on a table without antenna might fail, you really need some kind of antenna.

You should use the VirtualWire or RadioHead library. That is by far the best, anything else is not worth mentioning.

I think that the problem might be because the transmitters/receivers im using is too cheap then.. They have "The Coil" .. Ill look for some of better quality first off.. Can you provide a link to one of the right ones?

Which library do you use ?
When you have a library somewhere from the internet, it might have a range of 8 meters, and with the same hardware the VirtualWire or RadioHead can have a range 4 times that.

The receivers from Ebay with a coil are not very bad. But in a project with metal nearby, they might not work very well.
I use for example this one:
http://www.ebay.com/itm/181633631837 (this is the one that is more happy with a longer antenna).
These are cheaper, they look the same:
I don't know these at all:
http://www.ebay.com/itm/400899168249 (according to the description only -107dBm, not good enough).