You now have my attention. Is it something I can buildThe answer is that it depends on how much you are willing to spend and how much time you want to invest in the effort.
Part of this depends on how far is "extended"?I often install automatic gate's and garage door openers. The question I am always asked is if the gate / door range can be extended.
I would like to find out if this can be done and how
I have seen this done and it works WHY I have never had an answer to thisPush the remote transmitter into the neck under the chin and push the button. 200% range improvement guaranteed.
Extend range by:
1. antenna with higher gain on both receiving and transmitting end
2. increase transmitter power
3. situate T & R antennas so no obstructions.
4. use externally mounted antennas and minimize transmission line losses.
This is general only and not necessarily all inclusive.
I have one of these and while they now advertise range over 50 meters I was getting about 100 meters in open line of sight. Originally we used them as a backup safety device. I had good luck at short distances going through thick concrete walls. I have also seen cheaper versions. The one I have was left over from the initial testing. The boards can also "learn" something like 15 key fob transmitters.100 meters is more than enough. I would like to build one. I am going to post information about the transmitters and receivers
Maybe.
First thing to determine is the frequency band used by the transmitter and receiver. Next thing to determine is transmitter output power and receiver sensitivity. You can rent test equipment in most places to make these determinations, but it won't necessarily be inexpensive. In every country on the planet there are legal limits for unlicensed radio transmissions, so you need to know what those limit are. If your transmitter is operating at the legal limit and the receiver can be tweaked to increase its sensitivity then you have a great starting point.
If you don't want to fool around with the electronics then you need to work on the antennas. A wire stub radiates in an omni directional pattern. That is the available energy is directed in all directions. So the receiver has to pickup only a tiny fraction of the available power. So you need a transmit antenna that is highly directional and concentrates the available power in a single direction, in a very narrow beam. It helps if the antenna is closely matched to the transmitter's output impedance. This matching eliminates reflections which reduce the available radiated power. Plans for the consruction of a directional antenna can be found on the interwebs and are doable by anybody with a bit of maker skill. The problem comes in testing and debugging which requires some test equipment and some know-how.
Alternatively you could hire someone to do it for you if it is important enough. What you could charge for this range extension in your environment is something only you can answer. I can imagine it might be a "price is no object" situation.
Many commercial products have an available datasheet that gives the specifications. That is where I would start.
An antenna analyzer is used to measure the impedance of the antenna. You would need one that went up to the band of interest, 433 MHz.
What you do is start with a design, like a quarter wave vertical, and you make it bigger than it needs to be, which means that it is resonant at a lower frequency. Then you trim a bit off and test again until you get the minimum return loss. When you have minimum return loss on a transmitting antenna then you are radiating most of the output power. If you have a directional antenna matched to your transmitter then you can direct more of the transmitter's power in the direction of the receiver.
Receiving antennas are not as critical as transmitting antennas when it comes to impedance matching. Receiver sensitivity can be enhanced in two ways. You can use an amplifier to boost the input signal and/or you can use a filter to narrow the bandwidth of the received signal. This is where having knowledge of the receiver design comes in. As has already been pointed out some designs are very cranky when you mess around with them.
by Aaron Carman
by Duane Benson
by Duane Benson