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3 EASY ANTENNAS FOR BEGINNERS

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  • SpaxmoidJAm
    replied
    careful this is turning into a not so easy antenna thread.

    Leave a comment:


  • abcd567
    replied
    @RIN67630:

    https://en.m.wikipedia.org/wiki/J-pole_antenna

    http://www.hamradio.me/antennas/impr...e-super-j.html


    Last edited by abcd567; 2016-03-31, 20:25.

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  • abcd567
    replied
    Originally posted by RIN67630 View Post
    Has anyone got the dimensions of the Flightaware 1090MHz filter?
    Could it be, that its metal can has intrinsically the correct dimension to work as a cantenna?
    so the easiest way would have been just to stick a 68mm long piece of wire in its input and to wind 4 loops of cable at the other side to build a balun?
    This is not going to work. The basic requirement of a coaxial antenna (and it's wide-bodied varient Cantenna), is that the sleeve is connected to ground at top, but isolated from ground at bottom. The cylinderical metallic housing of Flightaware Filter is connected to ground both at top & bottom. Please see the drawing below.

    Please note that the coaxial antenna at right, although an old design, was not very popular as it did not have as good performance as other dipole designs. I realized that the narrow dia of copper pipe/tube has resulted in very narrow air gap between coax and tube, and this was the main reason of its poor performance. I then decided to use a much larger dia sleeve to enlarge the air gap, and this proved successful, and was birth of the Cantenna. I did try narrow dia sleeve made of 3/4 inch (20 mm) dia copper pipe, another with medium dia (54mm) drink can, and third with wide dia (68mm) Pepsi can. The 68mm dia can proved best, and 20mm dia pipe proved worst.

    (English translation in red added by me)

    Last edited by abcd567; 2016-03-29, 23:25.

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  • RIN67630
    replied
    Originally posted by abcd567 View Post
    The trickiest thing in J-pole, Slim Jim and Franklin dipole with matching stub is the accurate placement of cable tap off on the stub. At Ghz frequencies, few mm away from optimum point, and the antenna transforms from "very good" to "poor".
    I made another antenna deliberately placing the tap point 12 mm from the bottom:
    DUMP1090-Antenna2.jpg

    That one worked also pretty well, maybe the right point is around 9mm?
    Anyhow these antennas are really easy to build and perform much better than the shortened stock whip.

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  • RIN67630
    replied
    Has anyone got the dimensions of the Flightaware 1090MHz filter?
    Could it be, that its metal can has intrinsically the correct dimension to work as a cantenna?
    so the easiest way would have been just to stick a 68mm long piece of wire in its input and to wind 4 loops of cable at the other side to build a balun?

    Leave a comment:


  • abcd567
    replied
    Originally posted by jrf View Post
    Looking at the dimension calculation for the J-Pole and your picture: the feed point and spacing shall be 0.006 m = 6 mm. Did I misunder this or is your spacing bigger and the feed point in a different distance? As I read in another post it makes a huge difference if the feed point is just a little bit off the correct postion? Just asking because I might give it a try...
    Originally posted by RIN67630 View Post
    I have been using ~1,7mm wire. The distance is to be measured from the metal surface to metal surface, not from center to center.
    Additionally the formula ist valid for a rectangular J shape. The bend radius of the wire being quasi circular, the distances should approximately match.
    Of course it could be optimized, but then you need a HF-sender and a SWR meter.
    I have not yet built any J-Pole, but during 2013/2014 did experiment with Franklin dipole having an impedance matching stub.
    Please see my 2013 post here: http: //forum.flightradar24.com/threads/3831-best-antenna?p=43396&viewfull=1#post43396

    1) It was made of core wire of RG6 coax, which has 1 mm dia (18 AWG).
    2) The stubs were U shaped and not rectangular. I found the optimum location of coax tap-off point at 18 mm from tip of U.
    3) Tried two matching stubs with different gaps between parallel wires of the stub, one with 10mm and other with 5mm gap. Found 5mm gap gave better results.


    .

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  • RIN67630
    replied
    I have been using ~1,7mm wire. The distance is to be measured from the metal surface to metal surface, not from center to center.
    Additionally the formula ist valid for a rectangular J shape. The bend radius of the wire being quasi circular, the distances should approximately match.
    Of course it could be optimized, but then you need a HF-sender and a SWR meter.
    Last edited by RIN67630; 2016-03-23, 10:48.

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  • jrf
    replied
    Originally posted by RIN67630 View Post
    Here ist the detail view of the balun und the coax connection:
    http://www.cjoint.com/doc/16_03/FCwi...322-090136.jpg
    The dimensions are given here:
    http://www.hamuniverse.com/jpole.html
    Looking at the dimension calculation for the J-Pole and your picture: the feed point and spacing shall be 0.006 m = 6 mm. Did I misunder this or is your spacing bigger and the feed point in a different distance? As I read in another post it makes a huge difference if the feed point is just a little bit off the correct postion? Just asking because I might give it a try...

    Leave a comment:


  • RIN67630
    replied
    Originally posted by Sam26K View Post
    They key to minimal loss between antenna and receiver is to put the USB stick as close to the antenna as possible.. USB sticks are cheap, good quality low loss coax is not so cheap. If you use a good quality USB cable you can easily have a run of 15' feet from the USB stick to the pi or computer without a problem with 5VDC source loss.

    Otherwise if you have a long run of coax from the antenna to the receiver, an inline amplifier is the solution. A power supply is required. Did anyone come up with a good solution for the inline power amp? TIA!
    Full ack!

    If you want to build a cantenna, the easiest and far best way is to use only the F-pigtail and directly house the receiver stick inside the can.
    You may use a 10m usb repeater cable that will not cost much more than the 10m F-cable that you won't need anyway.
    Forget amplifiers, avoiding losses in HF lines is much more efficient!
    Every additional HF connection weakens your signal, the receiver has enough gain anyway!

    By the way: you should use a 10cm stable food can. It can be fixed using cheap sewing pipe clamps.
    You should also cover can and antenna with a matching plastic funnel, else water will accumulate onto the can. :-(
    Last edited by RIN67630; 2016-03-23, 08:06.

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  • RIN67630
    replied
    ...are we still under the topic easy antennas for beginners?

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  • skyspotter
    replied
    Originally posted by abcd567 View Post
    Since the antenna image does not say it is a jpole, there may or may not be a dc short. The best way is to check for short using multimeter. However there is no harm in installing a dc voltage blocker as a precaution.

    That antenna, is surely shorted. Omni directional antennas like this has a coil tap making it resonant to a frequency as advertised. It uses a capacitor to tap to the coil.


    Sent from my iPad using Tapatalk

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  • abcd567
    replied
    Originally posted by andrewh_85 View Post
    I recently acquired a similar antenna from ebay, I am connecting with a bnc to f connector into my dongle giving me great coverage.

    I also purchased a filter if I connected that will it help improve my signal?

    [ATTACH=CONFIG]7214[/ATTACH]
    [ATTACH=CONFIG]7215[/ATTACH]
    Originally posted by F-EGLF1 View Post
    What you picture is NOT a filter, it is an in-line amplifier, it will not do anything without a bias-t power injector and psu, and possibly a DC blocker depending on the antenna type you connect it to, if you just connect it as it is all it will do is block the signal and you will not receive any aircraft!
    With the correct setup then it might help if your signals are low, see elsewhere in the very long antenna thread for more details.

    Additionally I have just looked at the other picture you posted, you will almost certainly need a DC blocker with that antenna as it is probably a J-pole type.
    Since the antenna image does not say it is a jpole, there may or may not be a dc short. The best way is to check for short using multimeter. However there is no harm in installing a dc voltage blocker as a precaution.

    Leave a comment:


  • andrewh_85
    replied
    Originally posted by F-EGLF1 View Post
    What you picture is NOT a filter, it is an in-line amplifier, it will not do anything without a bias-t power injector and psu, and possibly a DC blocker depending on the antenna type you connect it to, if you just connect it as it is all it will do is block the signal and you will not receive any aircraft!
    With the correct setup then it might help if your signals are low, see elsewhere in the very long antenna thread for more details.

    Additionally I have just looked at the other picture you posted, you will almost certainly need a DC blocker with that antenna as it is probably a J-pole type.
    Cheers for the help. At the minute I just have it connected straight to the dongle. Is the below link the correct type of dc blocker. Would I just connect that between the antenna and dongle?

    image.jpg

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  • abcd567
    replied
    Originally posted by skyspotter View Post
    As a ham, i agree with you. Jpole is one best antenna for vhf band and up.
    J-Pole is a clever modification of an already established antenna, the "full wave dipole with impedance matching stub".

    First, the lower limb of dipole was removed to make it a monopole. Next step was a clever thing: bend down the phasing stub to make it inline with monopole instead of being perpendicular to it . This resulted in J-Pole to be an end-fed antenna, and made it's installation much easier than center-fed dipoles.

    The trikiest thing in J-pole, Slim Jim and Franklin dipole with matching stub is the accurate placement of cable tap off on the stub. At Ghz frequencies, few mm away from optimum point, and the antenna transforms from "very good" to "poor". At lower frequencies, where dimensions are big, it is much easier to accurately place cable tap-off.

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  • abcd567
    replied
    Originally posted by RIN67630 View Post
    So the box is on the roof:

    http://www.cjoint.com/doc/16_03/FCwo...322-150736.jpg

    Obviously + 250% more planes than indoors, although it was not my aim to get DX range.
    I get the traffic from Amsterdam to Frankfurt despite the fact that I am in a valley.


    The whole thing is mounted on a heavy stone plate, so I had not to drill in the roof.
    Seen the photo of your roof top installation. Great built, neat, elegant & crafty. Congratulations.

    Although you are not interested in DX, it s fun to find out what maximum range you can get from your location inside a valley.

    Please see this thread:
    What is the Maximum Range I can Get?

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