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Thread: A simple DIY antenna - an amplified dipole

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    A simple DIY antenna - an amplified dipole

    Simple Amplified dipole for ADS-B reception. If you want to suggest a different [unrelated] design please start another topic or discuss in the best antennas topic http://forum.flightradar24.com/threa...1-best-antenna

    There are three parts to this project:

    1. Construction of a simple dipole antenna for ADS-B reception for outside use
    2. Adding amplification to the antenna
    3. Mounting the antenna and amplifier to feed your rig.

    Tools and supplies: You'll need:
    a craft knife
    some good quality self amagamating tape http://www.ebay.com/itm/250825522803
    a quantity of 'F Connectors' http://www.ebay.com/itm/330982790603
    A hot melt glue gun

    a satellite amplifier http://www.ebay.com/itm/271413851182
    a power injector and 15v power supply http://www.ebay.com/itm/221523231893

    The simple antenna is formed by taking some coaxial cable suitable for use as a domestic satallite downfeed. This cable would have:
    a plastic sheath covering
    a copper braid covering
    a foil shield covering
    a 'non-foam' dielectric insulator
    covering a solid copper core

    Typically it would be 6mm diameter.

    Cut about 100mm off the end of the cable - strip a little of the end of the cable, then pull the core + insulation out in one piece
    bare 20mm of the copper core and bend at 90 degrees

    strip the about 80mm of the uncut cable, removing the outer sheath, copper braid and foil.
    Bend the inner core and insulator through 90 degrees.

    now insert the 20mm copper core of the first piece so it slips under the sheath on the second piece forming a tee with two arms 80mm long.

    This is a simple dipole - we need to cut it down a bit and it's not very robust. It would fall apart easily.

    Put a blob of hot melt glue over the joint. This serves two purposes to hold the joint together and to waterproof it (sealing the sheath to the insulator on both cores)



    Once this is done cut the arms of the tee off to 68mm each

    THis is a diagram of a similar dipole but without the glue



    While you have the glue gun out put a small blob on the ends of the arms to seal then against the weather.

    This dipole on its own should give you a range of 80-100nm (nautical miles) or 150-200km, mount it so the arms point up and down and the cable comes out sideways (see the first picture, ignore the amplifier)

    Now we'll fit the amplifier

    Cut your coaxial cable about 100mm from the tee

    Fit F-connectors to both ends (see https://www.youtube.com/watch?v=sksyX32PPMc - I don't have a fancy cutter, I use a craft knife)

    Fit the amplifier - make sure you get it the right way around - the word ANT or LNB connects to the diapole, the other end connects to the remaining length of cable.

    We need to cut the other end of the cable in the same way - you might need a bit more length left - to insert the power injector box.

    The injector has three connection points, don't mix them up or you could destroy your receiver

    One is marked ANT or DC+HF - this connects to amplifier at the other end of the cable via the long cable
    One is marked TV or HF - this connects to your receiver
    one is marked DC or power - this connects to the 15v wall block power supply

    Get your antenna up and in the clear with the amplifier on and you should have a range of 200nm 375km or more.

    Now you need to waterproof the amplifier - wind self-amalgamating tape around the amplifier and the f-connectors both ends leaving no gaps. Some say start in the centre, work out to one end, keep winding back over the whole amplifier to the other end then work back into the centre - that gives two layers over the whole thing.

    see https://www.youtube.com/watch?v=fJPOYCDH8wE

    Now fix the antenna to the tee is away from the support and the amplifier is horizontal - I just cable tied mine in place.
    Consider fixing a sun shade over the amplifier (having made it black the sun will cook it)

    Then fix the support so the tee is a meter or so higher than your roof ridge. This is light enough that you could just use a bamboo bean pole as the support temporarily

    Done

    ----

    Three screenshots
    (1) taken with amplified dipole 30 cm below...
    (2) taken with amplified Bulgarian collinear
    Capture3.PNGCapture2.PNG

    Virtual Radar range diagram - the outermost ring is as 225nm - just take the maximum distance as range, other directions just mean on planes went there or there are obstructions in that direction.
    Last edited by peterhr; 2014-08-30 at 08:06.

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    Captain abcd567's Avatar
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    @peterhr:
    Excellent writeup. Thanks.

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    I am adding a sketch to graphically elaborate some of the steps in peterhr's post above:

    Last edited by abcd567; 2014-10-06 at 03:14.

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    If this is going to be mounted externally do what you can to prevent water being drawn into the assembly

    use a sealing blob of hot-melt glue where the 'T' joins.

    Put a blob of hot melt glue on the ends of part 'B'

    if the insulator on the vertical parts is foam ... waterproof it with spray varnish or something.

  5. #5
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    I've built a simpler version of this antenna (i.e. without amplifier, insulator or waterproofing/gluing) and can confirm it works very well given its simplicity. On the roof of my two-storey house next to my UHF TV antenna, my current maximum distance is about 430 km, with reliable/consistent reception up to around 350 km. Cable run is about 2 or 3 metres unamplified, connected to a laptop and Realtek dongle in the attic - not sure how much improvement amplification would bring.

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    Hi eastons, any chance of a picture or a diagram? Thanks

  7. #7
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    Quote Originally Posted by eastons View Post
    I've built a simpler version of this antenna (i.e. without amplifier, insulator or waterproofing/gluing) and can confirm it works very well given its simplicity. On the roof of my two-storey house next to my UHF TV antenna, my current maximum distance is about 430 km, with reliable/consistent reception up to around 350 km. Cable run is about 2 or 3 metres unamplified, connected to a laptop and Realtek dongle in the attic - not sure how much improvement amplification would bring.
    Amplifier adds little to the range (maybe 5%) but does bring in more planes from within the range ... possibly they're putting out less signal in your direction.

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    Hi trigger,

    It's essentially the same as peterhr/abcd567's specifications - but without the protective elements and amplification. Nevertheless, since you're interested, I've attached a picture of it and my range diagram for the past week (circles are 50 km apart - the outermost being 450 km). I have many hills and high-rises blocking my line of sight in many directions, so that's why my range is compromised in many directions.
    Attached Images Attached Images

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    From the photo it looks like your TV antenna reflector grid is blocking your signal from that direction - I would expect that you would see a significant improvement in area of coverage if you could mount your ADS-B antenna well clear of the TV antenna - perhaps lower on the mast.
    As for an amplifier, I suspect that you would see little to no improvement from using one, due to your short (2-3 metre) feed cable. The main function of an amplifier is to compensate for signal loss in a long cable run, i.e. if the antenna picks up a weak, distant signal, that signal may not reach the receiver if it has to travel down 20 metres of lossy co-ax - in such circumstances, an amp at the mast-head can boost the weak signal so it can reach the receiver. On the other hand, if the signal is just not being picked up due to a poorly constructed or badly sited antenna, then amplification will be no help at all.

  10. #10
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    I did actually have the antenna up higher (i.e. 1 or 2 metres above the UHF yagi) previously, but my reception/range actually worsened in all directions. I surmise it's because the longer 5-metre cable I used resulted in more cable loss than was gained by the extra metre or two of elevation. I suspect if I had a low-noise amplifier near the aerial (like in peterhr's photos), I'd be able to raise it and increase my range also, but I'm on quite a tight budget at the moment. When I did have it up higher, the extra elevation didn't really change the antenna's view much - the high-rises near me are also on a hill/ridge, so there's no chance of me being able to out-elevate them. I've also tried lower - that also reduces the range due to being below peaks of the immediate neighbours' roofs. So strangely enough, being in the middle of the UHF aerial gives me the best range.

    The ADS-B signals seem very sensitive to cable loss - i.e. even just 2 extra metres caused maybe a 50 km loss of range. But I suppose that makes sense, since I'm focusing on the distant signals that are already on the edge of decodability. My ADS-B antenna is also right next to the TV aerials' diplexer/masthead amplifier (since that does have a long 20-metre+ run to the TV sets) and I wonder if being that close to the masthead amplifier has any significant/noticeable impact on the ADS-B signals.

    Kind of off-topic to the dipole, but there are some pretty strong NFM signals around the 400/500 MHz range being broadcast from near my location and when looking at the 1090 MHz spectrum in SDR#, the images of those transmission are right in the middle of the ADS-B transmissions. I'm surprised I still get the range I do and that the ADS-B signals don't just all freeze up when they're talking on those NFM transmissions. I know a band-pass filter would help with the issue, but again, out of my budget, unfortunately.

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