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Thread: best antenna

  1. #2261
    Captain abcd567's Avatar
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    Quote Originally Posted by kucengemok View Post
    yup..one of my friends is suggesting this new type of antenna to be used for 1090mhz..is it possible?
    Please ask your friend to give a link to the manufacturer's/seller's web page for this type of antenna for 1090MHz.

  2. #2262
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    thank you abcd567, one last question.

    i need to tilt the antenna 35° because its to long for my attic.
    any bad effects on reception when i do this?

  3. #2263
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    Quote Originally Posted by STR_EDDS View Post
    thank you abcd567, one last question.

    i need to tilt the antenna 35° because its to long for my attic.
    any bad effects on reception when i do this?
    Yes, tilting antenna reduces range & output, but you can minimize the loss by:
    (1) Tilting in the direction shown in the attached sketch.
    (2) Keep the tilt as small as practically possible.

    Antenna Tilt.PNG

  4. #2264
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    In search for inspiration for improving co-linear antennas, I finally bumped into this thread.

    http://forum.flightradar24.com/threa...ll=1#post53161

    The "super Antenna" made by 1090 MHZ is indeed interesting.
    If you can approximate the corrugated shape of the outside shield to a sine, the additional length you get is 1.22 compared to a straight line.
    Guess what, 1/1.22 ~ .82 which is very close to the velocity factor for this type of cable.
    This means corrugated cable might be the "perfect" solution to solve the dilemma to achieve at the same time a half wave resonant frequency on the outside shield and a 180 phase shift between extremities.
    As soon as I can find some corrugated cable, I will verify with my VNA if the resonant frequency is indeed around 1.22 below the physical length.

    The other critical point is the decoupling which very often make co linear antennas very unpredictable when the cable becomes part of the antenna radiation.
    Seems the decoupling is also working well here.

    JLD
    Last edited by JLD; 2015-02-23 at 14:42.

  5. #2265
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    Quote Originally Posted by JLD View Post

    ....snip....

    This means corrugated cable might be the "perfect" solution to solve the dilemma to achieve at the same time a half wave resonant frequency on the outside shield and a 180 phase shift between extremities.

    ......snip.....

    As soon as I can find some corrugated cable, I will verify with my VNA if the resonant frequency is indeed around 1.22 below the physical length.

    .....snip.....

    JLD
    Greate! Very promising. Looks like the CoCo puzzle is about to be solved. Waiting for your VNA measurement results.

  6. #2266
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    Well, started to search where to find corrugated coax in EU but does not seem easy!
    Any input is appreciated!

    Until I find some corrugated, an alternate way to increase electrical length compared to physical length is to use larger diameter tube / coax.
    I will measure today what is the correction factor to be used with a few different size of copper tubes and coaxial.
    I will start with 11mm coax cable.

    JL

  7. #2267
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    its called: Cellflex cable
    Available at ebay. But its very expensive
    Last edited by STR_EDDS; 2015-02-24 at 17:13.

  8. #2268
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    Maybe I will just have to wait to get some corrugated from the US
    If the theory works, the nice thing about corrugated is that it would increase electric length independently from frequency, which would be nice for lower frequencies (VHF com).

    For the high frequencies like 1090 Mhz, I just verified that using large diameter coax should also be a solution.
    I removed external protection from RG213 type coax which makes it 8mm diameter at the braid.
    I had to get down to 60 mm to resonate as quarter wave at 1090 Mhz.
    This means that the physical size is around 88% of the electrical size.
    Also confirmed that with this diameter, the bandwidth of the quarter wave is very wide and therefore the resonance frequency not so much an issue.
    The impedance at resonance is also low (~25 Ohms against a ground plane)

    This means that it is critical to cut the coax pieces to be exactly a half wave from a phasing stand point (half wave x VF) and if the coax is anything from 8 or more mm at the braid, the braid will resonate well at 1090 Mhz.

    Will try during the weekend.

    JL

  9. #2269
    First officer 1090 MHz's Avatar
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    Glad you like my Super Antenna! Its design is based on a professional grade 1100MHz DME antenna. Those antennas are Mil spec & FAA certified and are extremely expensive.
    I wanted to make something low cost with the same or close enough results.

    The LDF1-50 coax is nice stuff to work with as it’s a copper pipe and cuts easy and precise with a copper pipe tube cutter. As you will see here 32 rings in length was resonant at 1090 MHz ½ wave. http://ads-b.ca/antenna-collinear-F-CYYZ2/img_9689.htm

    I was lucky enough to have been given for free over 400 feet of LDF1-50 coax after the localizer/glidepath was rewired on 15 L at CYYZ. The coax is 15 years old, but was encased in conduit, and was in great shape, except for a few kinks I had to cut out that was a result of it being removed from service.

    My neighbor and friend from Nav Canada, that was nice enough to give me the coax, came over a few weeks later to test out my antenna. He brought with him their VNA scope and ran various test. He was impressed and said for a home made antennas that it preformed very well, good enough that the antenna passed all of their required tests and that he would certify it for legitimate ADS-B and DME use … it work that well.

    I have loads of LDF1-50 coax if anyone is in the Toronto area and wants some… email me at radar@ads-b.ca

    coax.jpg

  10. #2270
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    If the braid is resonant at 1090 Mhz then it confirms that the corrugated effect changes the braid resonance the same way the velocity does it on the coax transmission (at least at 1090 Mhz).
    Wonder if it would have the same characteristics in the VHF range!

    I don't know if your friend has measured the return loss but if the antenna works well, it probably means that the decoupling sleeve is effective and the cable between receiver and antenna does not radiate much.

    One question: what did you use to adapt the decoupling sleeve to the brass tube?

    JL

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