I need a directional antenna for 434MHZ: what consequence (besides knowing it will be half the wavelenght of the one the 868MHz was designed for) if this is done with a 868MHz antenna?
Hi E,Thanks for the replies. Idea abandoned.
A fact of RF life is that if you want to transmit on frequency X, then you need an antenna which is either resonant at frequency X, or has a suitable matching unit so that the transmitter thinks that it is seeing an antenna characterised for frequency X.I am still on the lookout for alternatives for 434MHz antennas.
The fact that 1/4 wavelength gives me too large an antenna. So that is why I presumed that a 1/4 868MHz antenna will be 1/8 wavelength 434MHz antenna. Apparently not so. Although I cannot see why, just curious?(..)
What is your problem with using the correct antenna for 434MHz?
It's obviously 1/8 wavelength - but 1/8 is no good for an aerial.The fact that 1/4 wavelength gives me too large an antenna. So that is why I presumed that a 1/4 868MHz antenna will be 1/8 wavelength 434MHz antenna. Apparently not so. Although I cannot see why, just curious?
Using a 434MHz module a remote sensor needs to communicate with a master controller. Since power consumption needs to be reducec I need as low RF power as possible, and preferably directed at the master controller. The RF module I use is https://www.aliexpress.com/item/1pc...-1000m-Replace-Bluetooth-NEW/32717804563.html. That controller has a coil type antenna which is 250mm in length. Using the onboard SMA connector I can connect any other type of antenna equipped with that connector.(...)
EXACTLY what are you trying to do?, why does it have to be directional?, and why does it have to be so small?.
Hi Mike, what is ISM?I live in a rural part of Arizona. If I use a high sensitivity SDR receiver connected to an outside, elevated antenna, I can receive about a dozen different transmissions in the ISM band, centered on 443.900 MHz.
Some of them are coming from my own appliances, like a remote reading weather station, a remote thermometer in my wife's green house, etc. The rest come from ??? I have only about five neighbors that are within a radius of 500m, so the other signals are likely coming from them. I can only imagine how many different signals there would be if I lived in a dense urban area.
Being a ham radio operator, I have equipment that transmits in the 420 to 450MHz ham band. I have noticed that when I transmit, it completely kills the ability of any of the ISM devices to receive their respective transmissions. This is due to my legal 100W transmissions at, say, 440MHz, completely blocking the simplistic 434 MHz super-regenerative receivers (exactly one tuned circuit between the antenna and the detector) for the duration that I transmit.
Also, the damn super-regen receivers in the ISM gadgets radiate RFI hash back out their antenna for about +-2Mhz centered around 443.9. Hams have learned to avoid trying to do any weak-signal work close to that frequency. I can imagine that in an urban environment, the ISM band would provide useful communication only very short distances, based on the quantity of such devices that step on each other, and unrelated transmissions coming from Amateur and Commercial Spectrum users.
Distances to be covered initially will be no more then a few tens of metres. But later I plan on using it to cover distances of up to a few kilometres with line-of-sight.How far from the remote sensors to the main station?, and is it in clear space?.
If your remote sensors initiate their own transmissions, that means you can shut down the HC-12 entirely, and place the sensor micros in sleep mode, this means almost zero power consumption.
Then when the micro decides it's time for a reading, it powers the sensor up, does the reading, then powers the HC12 up, and sends the data back to the main station. In your case it would probably be a good idea to write the software so it receives an acknowledgement from the main station, and repeat the transmission if no ack is returned.
As you're talking about hourly or daily readings, then consumption really isn't any sort of problem, so there's no need to try and reduce the transmitter power.
For a few km you're likely to need directional yagis, but full size ones will be needed (possibly at both ends).Distances to be covered initially will be no more then a few tens of metres. But later I plan on using it to cover distances of up to a few kilometres with line-of-sight.
google ISM band 433MHzHi Mike, what is ISM?
Not gonna happen with $3 radios in the ISM band.Distances to be covered initially will be no more then a few tens of metres. But later I plan on using it to cover distances of up to a few kilometres with line-of-sight.
EU requirements: in what respect? EDIT: ok, I had not seen your edited post. EU requirements: I doubt if in the south of France they heard of it, let alone care about.