14-02-2015, 00:22
I'm sorry if what I'm gonna write will be boring, I'll just try to explain the bigger picture behind antennas:
No matter of what kind is the antenna, the coil it's there basically to increase inductance.
One of the "effects" is getting lower ressonant frequency. As in this case, size matters (the right size), as lower the frequency is, the bigger must be the antenna.
So if we want a smaller antenna, we know that the frequency that it will produces best results will be higher (the smaller the antenna, the bigger "it's frequency") and that's where inductance enters, by adding a coil increasing the inductance, the ressonant frequency will be lower, so, arranging the right inductance with the right size, it will be possible to have a smaller antenna for a lower frequency.
Without the coil and with the same antenna length, the frequency would be bigger.
That's why, those "coil antennas" like Werk_AG posted, will be smaller than others and at the same time, will work "well" on desired frequency (antenna's gain it's another question).
I guess I could roughly say something like, the bigger the coil, the smaller the antenna would be.
If you ever picked inside a regular radio receiver with AM, probably you noticed a big coil with hundred of turns ... that's precisely the AM antenna, it would be impossible to have an antenna with the needed lenght, not inside your home at least.
Werk_AG said that he tested some antennas that performed well in RX but not in TX, that could happen for many reasons like harmonics, bandwidth, etc
Imagine an antenna with large bandwidth (enough for receiving 433 signals), with no gain - that probably would not matter because the TX almost for sure is near. That would work for RX but when you try to TX, the result it's not the same. Probably the antenna will not resonate as it should on 433 or can even not resonate at all, that would be catastrophic and that's why it won't be good for TX and also because in the other side (on RX) you probably won't have a "super" antenna to compensate the problem you have on TX side.
If you are gonna have long distance from TX and RX, you can also think about a directional antenna, that would extend the range.
A good calculated antenna no matter its "style", will do a great job even with longer cable attached to it - the cable it's also important, but I guess it's better to stop with this because in a while, no one will be reading this post this far
ps. Sorry for the "off-topic lecture", I hope that no one has fallen asleep reading this ...
No matter of what kind is the antenna, the coil it's there basically to increase inductance.
One of the "effects" is getting lower ressonant frequency. As in this case, size matters (the right size), as lower the frequency is, the bigger must be the antenna.
So if we want a smaller antenna, we know that the frequency that it will produces best results will be higher (the smaller the antenna, the bigger "it's frequency") and that's where inductance enters, by adding a coil increasing the inductance, the ressonant frequency will be lower, so, arranging the right inductance with the right size, it will be possible to have a smaller antenna for a lower frequency.
Without the coil and with the same antenna length, the frequency would be bigger.
That's why, those "coil antennas" like Werk_AG posted, will be smaller than others and at the same time, will work "well" on desired frequency (antenna's gain it's another question).
I guess I could roughly say something like, the bigger the coil, the smaller the antenna would be.
If you ever picked inside a regular radio receiver with AM, probably you noticed a big coil with hundred of turns ... that's precisely the AM antenna, it would be impossible to have an antenna with the needed lenght, not inside your home at least.
Werk_AG said that he tested some antennas that performed well in RX but not in TX, that could happen for many reasons like harmonics, bandwidth, etc
Imagine an antenna with large bandwidth (enough for receiving 433 signals), with no gain - that probably would not matter because the TX almost for sure is near. That would work for RX but when you try to TX, the result it's not the same. Probably the antenna will not resonate as it should on 433 or can even not resonate at all, that would be catastrophic and that's why it won't be good for TX and also because in the other side (on RX) you probably won't have a "super" antenna to compensate the problem you have on TX side.
If you are gonna have long distance from TX and RX, you can also think about a directional antenna, that would extend the range.
A good calculated antenna no matter its "style", will do a great job even with longer cable attached to it - the cable it's also important, but I guess it's better to stop with this because in a while, no one will be reading this post this far
ps. Sorry for the "off-topic lecture", I hope that no one has fallen asleep reading this ...