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Topic: 433MHz RF receivers and antenna types (Read 486 times) previous topic - next topic

Lars81

I've been messing around with different types of cheap RF transmitters/receivers in order in order to maybe use it in home automation projects. So far I've tried to connect the receivers to an oscilloscope and look at the signals sent from other devices such as wireless switches, doorbell and so on and then emulate them with the arduino and RF transmitters. The receivers seem to pick up the signals, with varying results. First I tried to use a solid core wire on the receivers, but then I had to hold the wireless switch literally within a meter to get a signal good enough to read the pulses. Later I tried to attach a helical antenna (still 17cm, diameter approx 4mm) which was able to pick up a perfectly clear signal from the doorbell on the other side of the house, two floors below. However when I used the helical antenna the pulses are always ~130us longer than the pulses being sent. (I checked this by using the arduino to generate pulses on the transmitters). This was the case with different transmitters (different chips and on commercial devices as well).

Does the duration of the pulses depend on the antennas being used? I don't really understand the logic behind that the helical antennas picked up the signal so much better, but induced a lag on the high pulses (not the low pulses). With the whip antennas I was able to get correct pulse lengths, but poor reception.

jremington

#1
Mar 29, 2017, 02:03 am Last Edit: Mar 29, 2017, 02:04 am by jremington
Quote
Does the duration of the pulses depend on the antennas being used?
It certainly shouldn't.

Helical antennas generally do not work as well as simple 1/4 wave dipoles (17 cm for 433 MHz), although many factors affect the range in any given experiment.

However, you will get almost always get much better range and reception with a balanced dipole as shown below, on both transmitter and receiver. One inner connection is made to ANT, the other to GND. I easily get over 300 meters line of sight range with the configuration shown below. The dipole is 33 cm from tip to tip.


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