In my 433 MHz projects I have been using a cheap (1 euro) pair of Tx/Rx modules. I have mostly used the transmitter and that is actually pretty good: if used to trigger comercially available remote switches, it reaches very far with just a simple 1/4 lambda antenna.
The receiver however is a bit crappy:  without antenna the reach is  maybe no further than a meter, but even with a  1/4 lambda antenna it is marginally more, even with free Line of Sight.
For any serious project that involved receiving data it seemed I needed the much better (and more expensive) RXB8 receiver.
However, when mining the internet for a coil antenna (trying to improve on the lengthy 17.2 cm stick antenna) I came across a design of Ben Schueler, apparently once published in elektor magazine.
It is a so called coil loaded design consisting of 0.6mm  wire wrapped around a 2.5mm core. Ben’s pdf gives a good description with pictures.
The results with this antenna are very good. The distance (with the cheap receiver) that can be covered easily goes to 25 m with line of sight, but also in-house the distance will be increased reaching other rooms with concrete walls in between.

433MHz Coli loaded antenna
Antenna in use

18 thoughts on “Coil loaded 433 MHz Antenna

  1. I’m doing a small project in an Altoid Tin and trying to extend the antenna outside the tin with the transmitter and receiver inside. Do I need to put the antenna external from the tin or would the antenna work as well inside the tin? Would I need to extend the 17mm length to account for the portion of the antenna inside of the tin?

    1. I havent tested it, but I presume the reception and transmission within a closed tin container is not optimal.
      I must confess that I do not know enough from Antennaś to know if you shld extend the 17 cm, but I doubt it. The simple 1/4 lambda wire antenna is not aware of the tin around it, the transmitter will just generate a proper signal in the antenna and then part of that will be shielded.
      My suggestion is to keep the onset of the antenna as close to the surface of the container and then let the antenna stick out. I also would advise to use the coil loaded antenna in this article rather than the 17 cm straight wire antenna. For me and others it really made a huge difference

      1. I would think with a tin with a flat bit of metal backing the monopole antenna, you would want to keep it perpendicular to any hole in the chamber you make thru the tin. A bit of plastic thru the coil would work.

        Otherwise you will couple a lot of the RF into the metal of the Tin and either ground it out, or at least make the antenna radiation pattern a bit odd and directional.

        I wonder the same with your problems +Android, and the short ranges you are having problems with. Did you put the transmitter and receiver on turntables to measure if you have any lobes?

      2. No i did not try the turn table. I do not know much about antenna design, so when i found and tried the coil antenna and it did what I wanted/needed, i was happy with it. My lack of antenna knowledge already becomes clear when I read yr comment as I am not even sure what you mean with most of yr terms🙂 The chamber? is that the inner space of the coil? what is ‘the tin’?
        I have come across some other designs that I will try if I have time. This one too when I understand it🙂
        But I am sure others might be helped by your comment. Thank you

  2. I was using one of these helical coil antennas which were made for these receivers/transmitters. They are terrible, and are very nit picky about the angle in which it was positioned. I tried this out and they worked out much better than I expected. Plus using just wires, I could make practically an unlimited amount of it with the rolls of wire I have. Thanks for this, very helpful.

    1. Yes I know the one from AliBaba/Aliexpress and though cheap, still more expensive than just a piece of wire rolled into a coil as I described.
      I am happy mine gave you good results

  3. The quarter wavelength antenna is supposed to have a reflective (ground) plane beneath it in order to work properly. Try a half wavelength dipole!

    1. Thanks, You are right and i have experimented with a 1/2 wavelength but the ‘problem’ is the size.
      I presume with the dipole the other end should be connected to earth

      1. I am very interested in this experiment, if this experiment requires a different calculation like in general, and how do I make it?

      2. I think I lost you. Different calculation from what? ‘How do i make it?’ well that is explained in the article you just have been reading

      3. how to calculation this antena? such as determining, L, N, C ,D gain etc. is it the same as estimates usually?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s