Optimizing wireless doorchime circuit range

Hello you guys,

I've got this wireless doorchime with a promised range of 100 meters. But because of my needs, the transmitter will be placed close to the ground (a few cm) and the reciever about 140cm from ground. This give me a range of 26 meters on an open parking lot, and only 16 meters on the lawn.

So, what can I do to increase the range? I think the obvious thing to do is to modify the PCB antenna - am I right?

The transmitter antenna should be as small as possible (10-15cm in size), and the reciever antenna can be a bit larger (30-40cm in size).

Here are 2 high res pictures to study - it shows the PCB antenna and most of the circuits.

I would rather change the reciever antenna, since there are many rules and regulations in my country regarding radio transmissions. I presume this door chime respects those rules since it's a common supermarket product.

Regards,
Futterama

I see youve had a bit of fun with the receiver circuit :lol:

What you could do is disconnect the PCB antenna(cut the copper track), and connect it to co-ax so you can have your antenna up higher.

Actually, this was how the reciever looked like when I opened it.

What is a co-ax? I have tried to cut the PCB antenna, and solder a 69cm thin wire to the capacitor, this doesn't give much more range.

Can I somehow increase the sensitivity of the reciever?

Regards,
Futterama

Unfortunately You cannot increase the sensitvity of receiver. Most of case (like this also) is a superregenerative type. Need to build a superheterodyne (more complicated) and/or increase the transmitter power. If the TX is wrong position, no or not enough aerial, the higher power not helped.

Co-ax is a type of wire that keeps signals from radiating. Its like what you see coming off of a satellite dish. What you could do is take away the PCB antenna, and solder a co-ax wire to the capacitor. Then on the other end of the co-ax (which is higher in the air) you put an antenna. The higher the antenna the better radiation.

So the co-ax keeps the signal from radiating until it gets to the antenna which would be higher. This would increase range.

zachtheterrible, are we still talking about the reciever?

And oh, COAX cable, yes I know that, the way you spelled it, confused me.

If you are talking about the transmitter, there is not enough room to have a large antenna since the transmitter will be mounted on a 1/8 scale RC car.

By the way, both the transmitter and the reciever runs from 3V (2xAA alkaline cells), would it increase transmitting power if I used 5V instead of 3V? And would the reciever increase sensitivity by increasing the operating voltage?

I was talking about the transmitter.

While it is possible that increasing the voltage will increase sensitivity, I wouldn't try it because more than likely you will damage something.

What you need is a pre-amplifier for your receiver.

And I'm sure you know where I can find a circuit diagram for that pre-amplifier

Futterama said:

And I'm sure you know where I can find a circuit diagram for that pre-amplifier

Click to expand...

I wish I could say that I do :lol: Do you by chance know what frequency this circuit operates on?

Yes, it operates at 433.920 MHz.

Do you know what sort of modulation it uses? AM FM . . .?

Sorry I can't help you with a pre-amplifier, maybe someone else can.

No, I don't know about the modulation. Perhaps I should find someone local to help me build a pre-amplifier.

Thanks for your help anyway

Futterama said:

No, I don't know about the modulation. Perhaps I should find someone local to help me build a pre-amplifier.

Click to expand...

This is near enough the 70cm amateur band, there have been plenty of 70cm preamp designs over the years, or you can buy them ready built.

The reason I ask about modulation is that you can buy RF modules for 433MHZ. Some of these modules are more than likely much more sensitive than your receiver and you could combine the moudle and your receiver. Use the module to receive the signal, but still use the receiver to decode it.