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Thread: best antenna

  1. #2561
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    Quote Originally Posted by SpaxmoidJAm View Post
    your plan wont work, because if you cut to those lengths by the time you have trimmed of the outer needed to push the elements together they will non longer be the right length.

    see image, Attachment 7875

    that's your corrected wavelength
    Yes, sure the lengths given by me do not include the pins on both ends. This is the way element lengths are specified in all designs on internet. The maker has to add required extra length for pins as it suits him. Pin length is not critical to design, and can be anything from say 10mm to 30mm.

    Have you noted I mentioned to cut 6 lengths of 1.5 meters each? The length required without pins is 8 x 117 = 940 mm, say 1 m only. This additional 0.5 meter is for pins (8x2x0.025=0.4m).
    Last edited by abcd567; 2016-08-04 at 19:48.

  2. #2562
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    just wanted to make that clear to anyone reading the post.
    T-EGLF8

  3. #2563
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    Quote Originally Posted by SpaxmoidJAm View Post
    just wanted to make that clear to anyone reading the post.
    A wise step to cover my mistake of not mentioning "add to these lengths, the length of pins at both the ends" . Thanks.

  4. #2564
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    Time flies... but in the meantime I managed to work a little on the air gap coco, ordered one antenna from ebay, and soldered my best spider until now.
    The ebay coco is worthless, will try to sort it out with the seller.

    The new spider antenna works really great, over 200nm coverage, bulk of received messages is at around 100-130nm.
    It's a ~50nm improvement over my normal spiders/cantennas.

    For this spider I used one male F connector and one F female joiner. RTL side is covered by a MCX connector adapted (soldered) to the RG59/U cable I used.
    The cable is all copper with 0.6mm dia center wire. Attenuation is 13.02dB/100m at 100MHz, I expect it to be a lot over 30dB at 1000MHz.
    Since the cable length is about half meter, it should be fine.
    The second spider uses 11m of the same cable with identical reception. Weird, right?

    The only different thing that I did comparing to other spiders is that the central coax wire was left longer by an extra F joiner + whip length.
    The male F connector was mounted on the cable and the central wire was protruding by 10-11cm.
    This was mounted through the F joiner with the central wire coming through and exiting for about 70-80mm. I trimmed it to 68.8mm.
    On the F joiner I added some copper wire to allow the fixing nut to sit flush on the open end.
    4 copper wires (I used 1.5mm appliance cable here) were soldered on the fixing nut and trimmed to 68.8mm length each.
    Attached Images Attached Images

  5. #2565
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    @ccz
    At last, after long wait...
    Nice to read detailed report. At microwave, the hardware often behave unexpectedly. The net result is combination of many factors, and combination of little difference in each can result in substatial difference in overall performance.

    Glad to see you broke the tradition of using SO239 connector (good only for VHF) and N connector (for UHF) and used F connector which is designed for microwave frequencies. The idea of soldering the radials to the nut is good. Others who used F connector, have soldered radials on the washer.

    Since in the new spider you have placed few turns of wire below the nut, raising radials to the level where the whip starts, this might have improved the performance of your new spider.

    I have once tried to avoid SO239 and use an F connector, but also avoided soldering as I have very poor soldering skills. Click here (post #5) to see it.

    I also have tried to make a Spider without any connector at all. Click here to see.

    For outdoor use put few drops of hot melt glue or a sealent to prevent rain water or moisture entering the coax and corroding its braid and center conductor.

  6. #2566
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    @ccz:
    I did not understand your photo below. What is this? If you passed the core wire of feed coax all the way through the F female barrel to make the whip, then this is a very smart idea. I will also try this.

    Last edited by abcd567; 2016-08-17 at 18:55.

  7. #2567
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    Quote Originally Posted by abcd567 View Post
    @ccz
    At last, after long wait...
    Nice to read detailed report. At microwave, the hardware often behave unexpectedly. The net result is combination of many factors, and combination of little difference in each can result in substatial difference in overall performance.
    Amazingly unexpected and the slightest misalignment/length mistakes produces a unworkable fixture.


    Quote Originally Posted by abcd567 View Post
    Glad to see you broke the tradition of using SO239 connector (good only for VHF) and N connector (for UHF) and used F connector which is designed for microwave frequencies. The idea of soldering the radials to the nut is good. Others who used F connector, have soldered radials on the washer.
    To be sincere, I was put off by the price of those connectors and the fact that F ones are readily available in almost any stores. Plus that they are used for SAT frequencies was reassuring enough.
    The only specialty connectors I've bought are the MCX ones. I'm trying to avoid adapters or any other connectors on the cable run. As short as needed and as directly connected as possible seems to give the best results here.

    I did try at first soldering to the washer but it was not sturdy enough for me. The nut, if soldered properly gives a much tougher result.


    Quote Originally Posted by abcd567 View Post
    Since in the new spider you have placed few turns of wire below the nut, raising radials to the level where the whip starts, this might have improved the performance of your new spider.
    This and using a continous center wire from cable trough F connector then the F joiner and to the whip also helped a lot too.


    Quote Originally Posted by abcd567 View Post
    For outdoor use put few drops of hot melt glue or a sealent to prevent rain water or moisture entering the coax and corroding its braid and center conductor.
    I will mix some fluid bicomponent gle and pour it around. That should take care of any moisture even better than silicone.

    Quote Originally Posted by abcd567 View Post
    @ccz:
    I did not understand your photo below. What is this? If you passed the core wire of feed coax all the way through the F female barrel to make the whip, then this is a very smart idea. I will also try this.

    Exactly what I did, that picture is just to show an example that it is possible. At least with part of the F female barrels that I got.
    I hated the fact that the whip was always moving around and the connection is actually pretty flimsy since there is no cable and F connector to support it. Plus the fact that from whip to MCX connector there's nothing else besides the small cable run.

    I will have to post a picture of how I soldered the MCX connector to the RG59 cable.

    PS: the wire through the barrel was at one time a radial for a spider connected just by tightening the nut. They were each (3 doubles making 6 total radials) at different height on the F connector. Not the best option but it worked nicely for a few tests.
    Last edited by ccz; 2016-08-18 at 00:20.

  8. #2568
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    @ccz
    Great! Very innovative!
    Thanks for detailed explanation.

    Did you see my following two posts?

    (1) Radials tightened by the nut. Click here (post #5) .


    (2) The coax core continues to make an integeral whip. Click here.

    .

  9. #2569
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    I've seen them both a long time ago.
    I think that the inspiration for the integral whip came from your no.2 post.


    I had holidays but managed to finish 2 new antennas before leaving and tested them today.

    They are pretty directional after 80-90nm but before that distance I seem to receive a lot of planes too. Maybe a lot of them are due to reflections.
    The beam seems to be about 90 degrees wide. It catches double the amount of planes in that direction (compared to a 1/4 whip).
    The message rate at ranges over 80nm is greatly improved indicating that it really has more gain.

    It would be nice if it would be possible to stack 4-6 of these and feed them into 1 receiver but sadly it isn't possible from what I have read.


    Construction:

    Simple one:
    1 x sheet 25/25cm of aluminum
    1 x F connector
    copper wire (from RG cable or other sources)

    Double version:
    1 x sheet of 50/25cm of aluminum
    1 x F connector
    copper wire

    For both versions the sides of the sqares are 68.8mm.
    The antenna is mounted 34.4mm away from the reflector.
    I read that most people are shielding the main 2 posts that connect the antenna to F connector/joiner.
    I have used the shielding from the RG cable for that.



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  10. #2570
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    @ccz
    Wow great!
    Bi-quad & double bi-quad. I never tried this, but you inspire me to make one. Will do it on some week-end.

    Mixing RF signals of 4 antennas and feeding to 1 receiver is tricky, and requires accurate phasing harness.

    Mixing in software (VRS, modeSMixer etc) 4 bi-quad is possible if each antenna is connected to its own dedicated receiver. For 4 antennas, 4 receivers (dvb-t) are required. This is a costly solution, but possible.

    Yes, I did use idea of integral whip, but it did not allow use of a connector. Your idea to pass the integral whip all the way through the F female barrel connector is brilliant.
    Last edited by abcd567; 2016-08-24 at 21:13.

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