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Antennas: 434MHz versus 868MHz

Discussion in 'Radio and Communications' started by earckens, Sep 14, 2017.

  1. earckens

    earckens Member

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    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?
     
  2. JimB

    JimB Super Moderator Most Helpful Member

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    The main consequence is that it will not work well.

    JimB
     
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    And will probably damage the transmitter, assuming the aerial is used for transmission?.

    As JimB says, for reception it will be seriously reduced in range.

    If you're using a directional aerial, it's usually in order to get better range - using one for the completely wrong frequency will not do that, and could be worse than a dipole.
     
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    It is like trying to turn a 10mm nut with a 5mm wrench.
    My 144MHz Yagi antenna is optimized for 144.1MHz. It doesn't even work very well at 147Mhz. Most antennas that get their directionality from parasitic currents in parallel elements are very narrowband. Some antennas can be used on odd harmonics of their design frequency, but not even order harmonics.
     
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  6. earckens

    earckens Member

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    Thanks for the replies. Idea abandoned.
     
  7. camerart

    camerart Active Member

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    Hi E,
    If you haven't completely abandoned your project, have a look at clover leaf designs. IBCRAZY has good information, if you google him.
    Camerart.
    EDIT: Sorry, ignore this, I read directional as omni directional, completely wrong!
     
    Last edited: Oct 2, 2017
  8. earckens

    earckens Member

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    Hi, well, not completely abandoned: I am still on the lookout for alternatives for 434MHz antennas.
     
  9. JimB

    JimB Super Moderator Most Helpful Member

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    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.

    What is your problem with using the correct antenna for 434MHz?

    One good thing about RF is that if you are using a low power transmitter which will not get all upset if it does not see the correct load on the antenna port, and, the path loss between transmitter and receiver is low, ie they are not far away from each other, then just about any old piece of wire will work - to a limited extent.

    JimB
     
  10. earckens

    earckens Member

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    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?
     
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's obviously 1/8 wavelength - but 1/8 is no good for an aerial.

    EXACTLY what are you trying to do?, why does it have to be directional?, and why does it have to be so small?.

    There's a book by the RSGB called 'The VHF/UHF manual', it might be worth seeing if you can source a copy - an old one would be fine.
     
  12. earckens

    earckens Member

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    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.
     
  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Generally directional aerial have to be specific sizes - but as you can run a cable to it, there seems little need for size constraints, and no need for portability (as it will need aligning, and leaving pointing in that direction).

    But your requirements are still pretty vague, presumably the remote sensors are battery powered? (you don't say), and do the remote sensors need to read from the master?, or do they just transmit at regular intervals?.

    To design any project, you need to know EXACTLY what you're trying to do, and what you hope to achieve.

    I've currently got seven temperature/humidity sensors running - four of them are mains powered, and use PIC16F1827's with HC-12 RF modules, these are read by the master every ten minutes (using an HC-12 and a Wemos D1 - originally I used a PC and HC-12 to do that), which then uploads the data to ThingSpeak.

    http://lpilsley.co.uk/new1.htm

    The other three use various ESP8266 modules, are battery powered and directly upload to a MYSQL database on my website - I don't have decent graphing sorted out for these yet, but the data is been stored regularly. The ESP's sit in sleep mode, and wake up every ten minutes or so to send a reading. Current consumption is nice and low, apart from the short bursts when they wake up and transmit.

    These are the types of things you need to plan, and how to optimise what you have.
     
  14. earckens

    earckens Member

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    Hi Nigel, for our house in southern France I am planning to install an automated irrigation system based on Arduino style controllers and sensors, of which a few will be remote installed and solar cell powered (soil moisture sensing, a thread for which I had opened somewhere else on this site), and uploading monitored data to Thingspeak.
    I have no precise idea yet how to conceive everything, your post hits the nail on the head re. concept.
    I am considering one central controller that receives data: for the wired sensors it would be based on polling, for the wireless remote sensors I had been thinking of the sensor initiating the transmissions (although I am not so sure anymore) on daily or hourly intervals. Sensor measurements from each sensor: soil humidity (remote, solar powered with HC12), and wired sensors: ambient humidity, barometric pressure and ambient temperature. Then some algorithm to calculate the required time of nightly irrigation and maybe some further gadgets.
    It is for the remote sensors that meaure soil humidity that I need the HC12 with solar power and this antenna. Maybe a directional antenna is overkill, I have no idea yet?
     
  15. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    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.
     
  16. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    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.
     
  17. earckens

    earckens Member

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    Hi Mike, what is ISM?
    Interesting input; I live in the centre of Ghent (https://www.google.be/maps/@51.0532...l8DbIVa-A!2e0!7i13312!8i6656?hl=nl&authuser=0) but the application will be used in https://www.google.be/maps/dir/43.8...,5.487895,166m/data=!3m1!1e3?hl=nl&authuser=0 , not exactly city environment.
    And I plan on using this setup as a demo, then selling to local vineyards where distances to be covered will be more in the km range. Therefor my interest in directional antennas. And there are no ham operators in the area there.
     
  18. earckens

    earckens Member

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    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.
     
  19. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    For a few km you're likely to need directional yagis, but full size ones will be needed (possibly at both ends).
     
  20. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    google ISM band 433MHz

    Read this EDN article.

    I would be surprised if the EU requirements are not more stringent.


    Not gonna happen with $3 radios in the ISM band.
     
    Last edited: Oct 2, 2017
  21. earckens

    earckens Member

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    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.

    Would this be of use then: http://www.embeddedworks.net/lpwan102.html ?
    He is using it: http://vanderleevineyard.com/vineyard-blog/archives/03-2016 and http://vanderleevineyard.com/vineyard-blog/archives/06-2016 and http://vanderleevineyard.com/vineyard-blog/archives/09-2016
     

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