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Thread: 3 EASY ANTENNAS FOR BEGINNERS

  1. #101
    Captain abcd567's Avatar
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    Quote 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?

  2. #102
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    Quote 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.

  3. #103
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    Quote 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

  4. #104
    Captain abcd567's Avatar
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    Quote 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?

    Attachment 7214
    Attachment 7215
    Quote 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.


  5. #105
    Passenger skyspotter's Avatar
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    Quote 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

  6. #106
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    ...are we still under the topic easy antennas for beginners?

  7. #107
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    Quote 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 at 08:06.

  8. #108
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    Quote 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...
    JRF: T-EDNY19
    South Germany

  9. #109
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    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 at 10:48.

  10. #110
    Captain abcd567's Avatar
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    Quote 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...
    Quote 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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