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RF Remote controller range increasing?

Discussion in 'Radio and Communications' started by bugeyed, Dec 11, 2010.

  1. bugeyed

    bugeyed New Member

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    I have an RF remote controller that I am adding to a project & want to get the max range possible. It's based on a 1527 chipset & 433MHZ. I use a key fob transmitter. The mfg. claims 150 - 200 meter range, but that's suspect. The receiver antenna is a piece of coiled wire probable about 10" long if uncoiled. Can I do anything with the antenna to maximize the sensitivity? I have the realestate to add more wire or a metal plate, so I am open to all suggestions.

    Thanks,
    kev
     
  2. RadioRon

    RadioRon Well-Known Member

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    Tuning both the transmit and the receive antennas should give solid improvements. The first step is to make the transmitter antenna much better because the antenna inside a key fob is going to be quite poor. Could you tolerate mounting the transmitter on a handle or pistol grip? This would allow you to add a more substantial tx antenna but be able to tolerate its size and weight. The tx antenna should be changed to a two element yagi made out of stiff wire, or to a dipole backed by a flat metal disc as a reflector.
    As for the receiver, the best you can do there without getting ridiculous is to make the antenna into a more ideal quarter wave monopole. For this to work, you need a metal disk or wire groundplane that has a radius of about a quarter wavelength. At 433 Mhz, and accounting for a reduced velocity on metal, this would be about 138mm. I've done this simply with four wires of this length, radiating away in four directions and bent down from horizontal by about 30 degrees. That ground plane should work well enough. The radiating element will tune well once it has this ground plane and you will find that 138mm is the right length for that too (plus or minus about 10% if you want to tune it)
     
    Last edited: Dec 11, 2010
  3. bugeyed

    bugeyed New Member

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    Thanks for your reply. I may try the receiver antenna you describe, but the TX needs to stay as is. Can you point me to a diagram of the antenna that you described? I'm having trouble visualizing the wires at 30deg & the metal plate combo. BTW This is going into a tennis ball machine (plastic case) & I am switching a couple of functions. I have a bit of vertical space inside on the right side, but not on the side facing the TX. Use will be line of sight < 100'. It may be fine the way it is, but since I am mounting the controller & relays inside, I would like to get it tweaked while I have it opened up.

    Thanks,
    kev
     
  4. dave

    Dave New Member

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  5. RadioRon

    RadioRon Well-Known Member

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    Antennas interact with their surroundings a lot. If you intend to integrate the antenna into the plastic case, I may not be able to suggest something practical without studying the available volume first hand. This is pretty hard to do via a forum like this. My suggestion of an ideal monopole requires that you place it on top of the tennis ball machine. This is because the interaction that I spoke of is most powerful to the sides of the vertical element. This means that if you place a vertical monopole alongside anything and especially metal, its performance will be degraded. However, if you place a monopole such as this on the very top, in the clear of any metal, the "ground plane" at its base isolates it from metal underneath, so no degradation occurs. The suggestion of a monopole, therefore, requires that you put it up on top with the vertical wire poking out from the top of the machine.

    If that is acceptable, then I'll describe it in a bit more detail. Now, I don't know if your receiver uses a coaxial cable to attach its antenna to the circuit board. Possibly not and in this case we have to do things slightly differently. If there is no coax joining antenna wire to receiver board, then we have to place the receiver board up at the top of the machine and extend the antenna wire vertically, straight up, a distance of about 138 mm from the surface of the receiver board. The "ground plane" will be made of four wires, called ground radials, all 138mm long that are soldered to the ground on your receiver pcb (close to the bottom of the vertical wire). The four wires are dressed outwards horizontally, or better, bending downwards about 30 deg or so, and in four different directions like the points of the compass. The length of these wires are to be trimmed so that the distance from the bottom end of the vertical radiating wire to the tip of each horizontal radial wire is about 138mm. That's about all there is to it.

    If there is coax, post again and I'll suggest how to handle that.

    I'm guessing that you may not be happy with having an antenna wire stick up above the machine. There are many other ways to do an antenna, but that is the simplest and most reliable, electrically speaking.

    this link shows a simple quarter wave vertical antenna. Scroll down to the second image, which shows a version fed by coaxial cable.
    http://www.radio-electronics.com/info/antennas/quarter_wave_vert/quarter_wave_vertical.php
     
    Last edited: Dec 11, 2010
  6. bugeyed

    bugeyed New Member

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    Thanks,
    I will have to take a closer look at the unit with what you have said in mind. The receiver doesn't have a coax connection. The antenna is simply a soldered wire that is coiled. It is about 1.25", but probably about 6" or 8" uncoiled. Would it help to extend this wire to 138mm & run it vertically? Here are some shots of what I am working with. No view of the inside of the machine though. Not much horiz. room, so if I can just extend the wire, it would be best.
    [​IMG]
    [​IMG]
     
  7. RadioRon

    RadioRon Well-Known Member

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    In a situation like this, the best you can do is uncoil the wire, and add on to it to make approximately 140mm mm long and then do some trial and error tests to see how you can arrange the wire inside the unit to give best range. Usually the best thing is to orient the wire so it drapes away from the board as straight as practical in any direction away from internal metal.

    It is possible to attach a coax cable to your receiver which would make it possible to use an external "rubber duck" style antenna, but it looks like such an external antenna would also get in the way of things.
     
    Last edited: Dec 11, 2010
  8. bugeyed

    bugeyed New Member

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    Thanks,
    OK, 1/4 wavelength is best? how about 1/2 wavelength or 280mm? I ask, because I can run a wire vertically along the front corner & that height is about 12". If I run the antenna down the front, I would have to mount the RX up there too, so the wire isn't too long. Know what I mean? BTW There is a metal plate on the bottom of the unit, so maybe run the wire horiz. along the front top edge? I guess I need to know if I can go longer with the wire than 1/4 wavelength.
    I really appreciate your attention to this. Getting this sort of help motivates me to tackle some other electronic projects.
    Thanks,
    kev
     
  9. RadioRon

    RadioRon Well-Known Member

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    We are guessing what feedpoint impedance the designers had in mind when they made that little coil of wire, but the safest bet is to keep the impedance relatively low. If you use a half wavelength of wire and connect the end of that to the receiver, you are likely making the impedance very high which is a bad thing. So if you want to try a dipole, you must use two quarter wave lengths of wire, connect one to the antenna point and the other to board ground and dress them in opposite directions so that the board is in the middle of the antenna. To be clear, you can try any length you like as you will not damage anything and in situations like this, experimentation is necessary anyway. Just be sure that you use a consistent way of measuring the range each time, preferably without cars driving within a few yards of where you testing and people should not be walking between tx and rx.
     
  10. bugeyed

    bugeyed New Member

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    Thanks, that makes sense. I know that I am not working with much of a signal here, so I don't want to increase the impedance. I can do the dipole if what I have doesn't work.

    Thanks again,
    kev
     

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