I was considering purchasing these small transceiver modules but am unsure about sizing the antenna. I recall having read somewhere that the antenna must be in proportion (wavelength/4) to the transmission frequency or reception is impossible.
From what I recall, transmission at 915MHz would approximately require a 8cm antenna or so. What are the benefits other types of antenna over basic wire types? And what do you typically consider when sizing an antenna? Can you literally solder a wire onto the device and expect to receive/transmit properly?
I am looking to use these devices no more than 50 feet or so. I have read conflicting data about the dependence on distance.
Not sure where to start with this.
Thank you.
Best Answer
Shortening an antenna from its ideal length is not a problem providing you accept and possibly counter the limitations that shortening brings. Here are some words from this site that tell you the story: -
The article goes on to demonstrate how the impedance of the antenna becomes reactive and how the idealized "50 ohm" input resistance becomes significantly less when shortening is done excessively.
Here is another excellent site that explains you can make an antenna from any length.
In short, any length works providing you can get the power into it that you require for transmission. Reciprocity means that a badly shortened antenna works just as "inefficiently" as a transmitter and receiver. There is no silver bullet of length - optimum is quarter, half and full wave antennas but don't let this stop you running the antenna at significantly shorter lengths.
One caution - if you are wanting to transmit several hundred milli-watts or above, not having an ideal antenna (proper length or compensated by matching networks) you may damage your transmitter output stage.