Hi Valent,
Your boards seem to have some similarity with the Bios/Thermor setup with RJ-connectors to skip the RF connection if required. However that aside, you also have another low frequency antenna there with the ferrite rod. I would guess the base unit can synch with the Radio Time signal?
Low detection rates can be either signal strength/Rx sensitivity or mismatch with the software.
I agree the long red wire curling around the top is most likely the 433MHz antenna. If you measure this it will give you an indication what it is tuned to. From memory, around 170mm is 433MHz. For these purposes it only has to be within ball park range to work well, though you might like to look up the exact length and maybe fine tune yours by changing the length. I would certainly start by attaching a wire the same length as the red wire to your Rx begin with. I am surprised that you are only getting that sort of reception. All of my current Oregon Scientific sensors are within6-7 meters, but do pass through the upstairs floor, and they are on top of a big corrugated steel roof, so a fair bit of shielding around, but they have been very reliable with very little data missed.
I am currently using the classic Rx design unlike the ones pointed to in your reply. I will add my circuit below that I use with them as I have found some of the 8 pin jobs have to be connected correctly, ie there are a number of "earths" to be dealt with. The piezo transducer (not a buzzer!) was added to the digital output during debugging to listen for data packets and I then watched on the IDE screen whether they were detected and decoded successfully or not. This could be worth trying for you as it would allow you hear if the packets were arriving (the white noise changes to a distinct chirp) and if your software may not be trapping them successfully. The OOK system is basically an analogue RF system adapted to send digital information. Unless the Rx amplifier is centered in the sweet spot of the signal, the on/off times can be become quite distorted and much harder to decode reliably. The AGC on the Rx has to be stable (hence the need for header bytes) and a good signal strength to turn AM bursts into a digital stream.
Likewise the software you are using may also need tuning as well for your situation. Especially if your piezo is indicating packet bursts are being missed. Manchester encoding (I presume you are using this sort of signal decoding) is quite tolerant and can be +- 15% out with the timing intervals and still manage to get many of the signals decoded correctly. However it is so much more reliable if it is closely aligned duration of the bit delays coming from your Tx. Some some experimentation there could be good.
Finally 433MHz receivers are fairly prone to RF noise, so I use a long USB cable on my 24/7 web server to get it away from the computer, however I found short ones while debugging on my laptop have been OK. The Rx and Uno set up was identical for both the Bios/Thermor and now the Oregon Scientific, just different software. I am about ready to post the latest OS software as there a quite a few interesting updates.
If you are after a higher quality Rx/Tx system have a look at the Dorji 433MHz line. I have used both at times, but just ended up getting my system to work first with the old classic 8 pinner Rx, and so have stuck with it. The Dorji though is a far superior design and technology. http://www.wiltronics.com.au/catalogue/200791/picaxe-rf-dorji-robots-kits/rf--dorji/dorji-ask-modules/dorji-fsk-rx-modules/dorji-433mhz-107dbm-ask-receiver--dip-package
Cheers, Rob
