scanning 5 antenna input ports

  • Checking for an antenna on a multi antenna switch.
    Looking for a way to read my HF antenna switch before booting up the transmitter. Need to scan 5 antenna inputs for an antenna.
    the scan must show if there is an antenna or if there is not an antenna.
    the circuit must be able to read a dipole or loop.
    would like to use an Arduino to do the scan and provide the feedback.
    Code will be build after circuit is found.
    The circuit will be switch to each antenna input vea a stepper so there will never be any RF to the circuit once the transmitter is keyed.
    Any idea will be explored.

  • Admin

    There are a couple of questions that you have to think about in such design: What kind of antenna? How much TX power do you expect to have from your transmitter? What frequency band are you looking at Etc

    The only real way (to my knowledge) is reading swr on the antenna, but that needs you to start transmitting, in order to read the returned signal from the standing waves.

  • @tbowmo
    The antenna will be a loop or a dipole, long wire,ect,ect
    No RF, this check will be made before the transmitter is turned on.
    The loop is no problem it the dipole that I am stuck on.
    The loop and open input can be done with a wheatstone brige .
    The wire or dipole not that easy.
    Need something to see the antenna without any RF.

    Any ideas? : )

  • Mod

    I'm just curious about what you are trying to build

  • Do your antennas have a DC resistance or a DC short? If so you could make a comparator circuit that would compare the antenna resistance to a known resistor value.

  • If you are just trying to see if the antenna is attached, then no antenna would be infinite or open, and an antenna would be somewhere around 50 ohms, wouldnt it?

  • @schlog
    Hi and thanks for the interest .
    The build is a auto HF antenna tuner it will support up to 5 antenna plus dummy load and 5 transmitters. with display of RF power in watts , SWR forward and reverse power, and tuning of the tuner will all be displayed on the front panel. Once the tuner has found the right SWR for the frequency it will be stored on a sd card for future fast tuning on that frequency.
    The circuit or idea of a circuit I am looking for is to scan and check all 5 antenna input and all 5 transmitter input to make sure that the transmitter is
    linked to an antenna or dummy load .
    This check will be done on booting up of the tuner (cold check ) before any transmitter is turn on.

  • @thetoybarn
    Yes and no the loop Yes there is a resistance that I can measure with an wheatstone bridge ,the open input will also so no change in resistance so I know it is open, again switchable.
    The dipole and long wire antenna have no return so there is no reading it looks like an open input.
    I am hopping for something that would still see the wire and return some kind of change that I can link to an Arduino or PI for controlling.

  • @wallyllama
    Yes and no .
    If I use an balun then yes it would be around 50 ohm but with out a balun the resistance could be up around 400 -600 ohm. the balun in the tuner will adjust the resistance once the system boots and the transmitter are turn on.
    But there needs to be RF for all this to work.
    I am looking for a way with out turning on the transmitter.
    The antenna and transmitter need to be checked before any RF is added .
    this check will make sure that any of the transmitter that are on line will be linked to dummy load or an antenna before power of the transmitter are turn on.
    An comparator circuit may work if it can see the dipole or wire antennas .
    There may be a slight change that a comparator could see , something for me to explore a little closer.
    But my meters all show no difference between an open input and the input of the dipole. But I will give it a try just to see if the change is so small that my meters do not show it.

  • @schlog it sounds to me like you want a basic antenna analyzer. Commercial ones arent cheap, and probably do more than you need. I did find a diy analyser for HF by K6BEZ, maybe it will inspire you.

    A time domain reflectometer might work, they are used to measure the length of cables, and dont require a return wire.

    it may work to measure the charge time of a capacitor, but I think the far end may need to be grounded.

  • @wallyllama
    Yep !! I was looking at them as one way to do this and it may be the way to go.
    I have two other circuits to look at before I go that way.
    1 is an antenna noise bridge and the other is a static detector both should give me some kind of feedback.
    But I feel you maybe be right and in the end I will just put in the analyzer.

  • @schlog you might be able to use a modified swr circuit, an arduino could generate a weak forward signal, and then use an analog input to measure the reflected signal ( sort of a TDR) instead of a meter, the impedance match will possibly be bad(maybe even on purpose to enhance the effect), but each type of antenna should be different enough that you can tell both if it is connected, and which antenna it is.

    Another thought, if this is permanantly connected, then you should only need to know the positions of the switches for the transmitters and antennas.

    Btw My call is:

  • Admin


    I was actually thinking in the same lane.. Have the arduino generate a low power signal, that could be used to measuse the antenna response, and from that, decide if an antenna is connected or not.

    But I think that this is way beyond the MySensors project (even though it it an interesting field 🙂

    "Vy 73 de OZ2AFO" 😉
    / Thomas

  • @wallyllama
    the modified SWR is a good idea I'll follow up on it.
    The scanning of the antenna input ports will show me if there is an antenna on that port or not.
    Yes I will know were the antennas are connected at any one time but the scan will allow me to know if the antenna is up or shorted and if not move the transmitter to a dummy load on boot up of the system.
    all the other auto tuners I have seen just move the antenna from one input to the next with no way of knowing if there is or is not an antenna on that input and what can happen is that you may end up keying to nothing.
    And could damage the finals in the amp or transmitter.
    With this scan on booting can move the transmitter to a safe spot .
    This tuner will be total auto . I want to be able to boot up the tuner and transmitter and have the tuner not only tune to the frequency but check and correct any antenna problems from the start.
    I still will be able to turn on or move any antenna on line that I want to use and I will be able to see from the from panel just witch input I have antenna on at that time.
    If you do a search on You Tube for ZT-1000 auto tuner you will get an idea of what I am building,
    I will be using most of his design but coding it myself, he is not letting the code of build out to the public.
    I have figure out from his video just how he has build the tuner .
    I can write the code and by doing so I can change how he treats the antenna and transmitter input ports.

  • @tbowmo
    I ended up building a swr circuit and just send a 433mhz signal .
    I know 433MHZ!!??
    It was a small transmitter I have laying around Gives me a real nice
    return single with an antenna on line and almost nothing with no antenna. Now I have to turn the return signal I can control.
    Going to use the Arduino to analog read the signal and give my a digital output. This gives me the control points I need.
    I can also use an external Analog to Digital convertor like the PCF 8591 but first going to use the Arduino to do the A/D conversion.
    Thanks for your help Ed NW4K 73's

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