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  • Scroggie
    replied
    Originally posted by abcd567 View Post

    I did make the one with 53mm long, 5mm dia, 16 turn coil, and did measure SWR. Please see this post:

    https://forum.flightradar24.com/foru...150#post184150

    However I did NOT make the one with your coil. You made it, and based on your measurements, I did computer simulation and posted results of simulation




    This is Flightaware antenna with pvc pipe removed.

    image_10493.jpg
    That is interesting - the top looks very similar to what we've been discussing but with a 4 or 5 turn coil. Could I please ask you to run your computer simulation using your measurements 60,53,137 mm but with 1.5 mm copper wire coil (1.54 mm with insulation) of 6.9 mm diameter (Wire centre to wire centre), 8.44 mm overall. It should be much worse than what you achieved but I'm curious as to how different it is to the 10 turn close wound.

    Scroggie

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  • abcd567
    replied
    Originally posted by Scroggie View Post
    Are you just using software to give those results or constructing the antenna and making measurements with a generator?
    I did make the one with 53mm long, 5mm dia, 16 turn coil, and did measure SWR. Please see this post:

    https://forum.flightradar24.com/foru...150#post184150

    However I did NOT make the one with your coil. You made it, and based on your measurements, I did computer simulation and posted results of simulation


    Originally posted by Scroggie View Post
    It would be interesting to see what's inside the commercial Flightaware antenna - must be something like this.
    This is Flightaware antenna with pvc pipe removed.

    image_10493.jpg

    Leave a comment:


  • Scroggie
    replied
    That's very interesting. I'm not seeing that 1dBi less gain with just a coil change perhaps because I see your calculation is using a 50 ohm feed impedance and I'm feeding the dongle with exactly half a wavelength of 75 Ohm coax (it's all I had to hand)
    I'll make one with your dimensions and compare them again. Are you just using software to give those results or constructing the antenna and making measurements with a generator? I don't want to take up your time unnecessarily but would be interested to know what the best coil dimensions would be using the thicker wire. I have no way of producing the detailed analysis that you do unfortunately.
    It would be interesting to see what's inside the commercial Flightaware antenna - must be something like this.
    Anyway thanks again for all your efforts, I'm sure it's appreciated by all on here.

    Scroggie

    Leave a comment:


  • abcd567
    replied
    Scroggie:

    Simulation shows that with your coil i.e. 10 turns, length of coil 16.3 mm, 5.1 mm inner dia, wire dia 1.54mm (mean dia 6.64mm ), the lower wire of 50mm length gives best SWR.

    Monopole with Coil 2 - Sweep Lower vs SWR.png


    Monopole with Coil 2 - Sweep Lower vs Gain.png


    Monopole Collinear With Coil - 50mm lower- Radials 45 degree down.png







    Leave a comment:


  • abcd567
    replied
    Scroggie:

    You are basing your designs on coil inductance only. Please also consider these effects of the coil:

    (1) The coil not only acts as inductance, but it also intercepts radio waves like the vertical straight wires do, and hence in additon, it acts as antenna wire also, and its height also counts.

    (2) The coil height determines the vertical sepertion between upper and lower straight wires, and this separation also affects antenna parameters & performance.

    It is a complicated situation. Simulation software take these two factors into consideration. When making actual antenna, trial and error can give you best results.

    Leave a comment:


  • Scroggie
    replied
    Coil Calculator.jpg This was the software calculation I used to calculate the required inductance from your measurements. There are online calculators as well and they don't agree with each other!! But this method did produce a working antenna. I think I might try adding another coil + another top 137 mm (I suspect that 130 mm is probably what is needed at the top because of "End effect" but haven't tried that yet - you found that I see above) I'm finding the ground plane radials difficult to construct tidily
    I'll watch this space and see how you get on - I'm self-isolating at the moment so have a lot of spare time!!

    Scroggie
    Last edited by Scroggie; Yesterday, 23:13.

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  • abcd567
    replied

    Originally posted by Scroggie View Post

    The wire diameter is actually 1.54 mm (1.5 mm + insulation) so if I had been able to wind it perfectly it would be 15.4 mm long but it was done rather crudely and actually it measures 16.3 mm. The plan was to make the inductance the same as yours which the software I used suggested was 0.212 microHenries. Even if that software wasn't accurate I figured that any error was the same for both calculations and it looks like it must have been more or less correct.

    Scroggie


    Thanks for providing the details of coil. Next weekend I will try to make one like yours and see.

    The mean dia of coil = inner dia of coil (which is the dia of drill bit on which the coil is wound) + dia of wire. It is mean dia of wire which is used in calculations & simulations.

    In your case the mean dia of coil is 5.1 mm + 1.54 mm = 6.64 mm.

    Leave a comment:


  • Scroggie
    replied
    Originally posted by abcd567 View Post

    thumbs-up.jpg

    Well done. Happy Experimenting.

    EDIT:
    What is the length of your 10 turn "close spaced" coil? My design was16 turns, 53 mm long coil.
    The wire diameter is actually 1.54 mm (1.5 mm + insulation) so if I had been able to wind it perfectly it would be 15.4 mm long but it was done rather crudely and actually it measures 16.3 mm. The plan was to make the inductance the same as yours which the software I used suggested was 0.212 microHenries. Even if that software wasn't accurate I figured that any error was the same for both calculations and it looks like it must have been more or less correct.

    Scroggie
    Last edited by Scroggie; Yesterday, 21:42.

    Leave a comment:


  • abcd567
    replied
    Originally posted by Scroggie View Post
    I've just remade it with a 10 turn, close spaced coil (1.5 mm enamelled wire) and still with 60 mm and 137 mm lengths and that has improved it by about 3dB (using the weakest signals showing on the graphs as a rough guide - see pic attached) I made the change at 18:48 and it does look promising. There are of course very few aircraft around to get the full picture.
    fetch?photoid=184359.png
    thumbs-up.jpg

    Well done. Happy Experimenting.

    EDIT:
    What is the length of your 10 turn "close spaced" coil? My design was16 turns, 53 mm long coil.
    Last edited by abcd567; Yesterday, 20:38.

    Leave a comment:


  • Scroggie
    replied
    I've just remade it with a 10 turn, close spaced coil (1.5 mm enamelled wire) and still with 60 mm and 137 mm lengths and that has improved it by about 3dB (using the weakest signals showing on the graphs as a rough guide - see pic attached) I made the change at 18:48 and it does look promising. There are of course very few aircraft around to get the full picture.

    Leave a comment:


  • abcd567
    replied
    Originally posted by Scroggie View Post
    abcd567:
    I had a go yesterday with some 1.5 mm copper wire (I don't have any steel and anyway I wanted to solder it to an F connector)
    Because my wire was so much thicker than yours I have ended up with an outer diameter of 8.4 mm - the drill I wound it on was 5,1 mm
    At first I mounted it in a north facing window and was a little disappointed until I looked at the same direction on my other outdoor antenna/receiver which showed very little traffic to the north of me anyway.
    Today I moved it to a south-east facing bedroom window and now it looks very promising. and this is with a coil of a different diameter! The other dimensions are the same.
    Now is not the time to get a very sensible comparison given that the daily count of aircraft I'm seeing has dropped from 2500 to 400 but considering the difference between the ranges from an 8 element coaxial colinear at 40 feet and your design in a bedroom window I'd say it's very successful. To only see 22 aircraft at what is normally peak time here is truly remarkable.
    Now I need to make another one, weatherproofed and mountable on my ham radio mast!


    Scroggie
    thumbs-up-3.jpg
    Great!
    Congratulations that you made a good wire collinear in first attempt.
    Try to make one or two more with few mm different lengths of lower and upper wires, and see if gives improvement. Make changes one at a time to know its affect. Do not change many dimensions simultaneously. By experimenting with trimming you can get an optimum design for your wire dia and your coil parameters.

    Leave a comment:


  • abcd567
    replied
    Scroggie:
    Software & calculations provide a starting point only.
    Finally it is trial and error, trimming and adjusting the built prototype.
    I built one based on calculation then startted trimming, it improved, then after a point worsened.
    The wire was cut smaller than the length where I got better results.
    I had to make another prototype with longer wire, and started trimming testing, but this time I was aware not to cut too much.
    DIY antennas are "trial and error" and "a shot in dark". Happy experimenting and good luck.

    Leave a comment:


  • Scroggie
    replied
    abcd567:
    My previous post has gone "unapproved" for some reason but I think it will appear eventually.
    In addition to that though I've been Googling coil calculators and found a very good one called Coil64-1.1.7 (Google it - I'm not sure if links are allowed in these posts)
    Anyway, using that software and your wire / dimensions it gives your coil a value of 0.212 microH and mine 0.232 microH. Reducing mine to 15 turns and I get something close to your value.
    Another option using my wire would be 10 turns closely wound (it is enamel coated) What do you think of that idea? - I think it would be more rigid and a little easier to make.

    Scroggie
    Last edited by Scroggie; 2020-04-05, 18:56.

    Leave a comment:


  • Scroggie
    replied
    abcd567:
    I had a go yesterday with some 1.5 mm copper wire (I don't have any steel and anyway I wanted to solder it to an F connector)
    Because my wire was so much thicker than yours I have ended up with an outer diameter of 8.4 mm - the drill I wound it on was 5,1 mm
    At first I mounted it in a north facing window and was a little disappointed until I looked at the same direction on my other outdoor antenna/receiver which showed very little traffic to the north of me anyway.
    Today I moved it to a south-east facing bedroom window and now it looks very promising. and this is with a coil of a different diameter! The other dimensions are the same.
    Now is not the time to get a very sensible comparison given that the daily count of aircraft I'm seeing has dropped from 2500 to 400 but considering the difference between the ranges from an 8 element coaxial colinear at 40 feet and your design in a bedroom window I'd say it's very successful. To only see 22 aircraft at what is normally peak time here is truly remarkable.
    Now I need to make another one, weatherproofed and mountable on my ham radio mast!


    Scroggie

    Leave a comment:


  • abcd567
    replied
    Scroggie:
    I wound the coil on 3/16 inch dia drill bit which is 4.76 mm dia (I do not have mm size bits).
    The wire used is thin steel tie wire, diameter aprox 0.5 mm (see the wire on floor in first photo below).
    I used thin wire as I found it easier to shape, and easier to wound on stud of magnetic base.

    Initially I made length of upper wire more than 137mm and after making, measured SWR by VNA. It was 2.1
    I then bend the tip of wire to reduce length and measured again, and repeated this till I got reading of about 1.57

    Optimized Whip Steel Tie Wire-R.jpg



    Coiled Collinear and Quarter Wave-2.jpg
    Last edited by abcd567; 2020-04-04, 22:02.

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