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2 Q about antennas.

Discussion in 'Radio and Wireless' started by plutes, Mar 14, 2021.

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  1. plutes

    plutes

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    Mar 4, 2021
    1, I have a handheld scanner and would like to know the best smallest discrete antenna design to build for listening to planes.

    something max 2ft tall so I can attach it to my guttering.

    2, And are we our selfs antennas? I build a lm380n amplifier on a breadboard, and Ive noticed when I pause the signal in, if I touch the pot I receive fm radio through it.
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    If it’s airband only, 108 - 137MHz should be about right.
    Many, many, many DIY ideas out there in internet.

    Guessing you are UK based as guttering is OUR word.
    Take into account the GROUND plane, is your guttering metal, cast or plastic?.
    You’d be far better getting it as high as possible on the chimney stack.
    Or use a good mobile antenna on a good metal ground plane.
    These can be bought fairly cheap too.
    And yes, the human body is a great antenna while also being a great path to ground.

    Martin
     
    plutes likes this.
  3. bushtech

    bushtech

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    Sep 13, 2016
    while also being a great path to ground.

    Take note when playing with antennas
     
    plutes likes this.
  4. plutes

    plutes

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    Mar 4, 2021
    yep UK, its plastic. And I live in a flat so I do need permission. I watched antenna 101 last night "YT", it had me thinking of 5 parabolic style antenna, and what I was thinking was making them out of fibreglass and in each one have a copper spiral in each the dishes glassed and a further two short exposed antennas in the middle offset at 90degress.

    I think, I think too much, and am not even sure if combining the 5 even would work?
     
  5. davenn

    davenn Moderator

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    A discone antenna is the fav wideband antenna for use with scanners

    [​IMG]


    there's DIY kits on the net, also ebay sales if you want to go that way
     
    plutes likes this.
  6. davenn

    davenn Moderator

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    too difficult to build, specially ? if ? you have no experience
     
  7. plutes

    plutes

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    Mar 4, 2021
    yeah I'm up for building one, I can get tons of fibreglass etc from my boat club, idea came out of having to build something similar for my parabolic microphone kit.

    would it work combining something like that, they wouldn't cancel each other out?
     
  8. davenn

    davenn Moderator

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    Sep 5, 2009

    You need to understand that small parabolic dishes at aircraft freq's 118 - 134MHz are useless as far as gain goes
    So you are making a huge effort for nothing
    This is why I suggested the discone as it is so so much easier to build :)
     
    plutes likes this.
  9. plutes

    plutes

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    Mar 4, 2021
    I just read this and I see your point, I might do both, get a £40 discone for my scanner and attempt to build a array of parabolic dishes, and pair it with a cheap sdr.


    Good article
    https://www.qsl.net/n1bwt/chap4.pdf
     
  10. plutes

    plutes

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    Mar 4, 2021
  11. bertus

    bertus Moderator

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  12. plutes

    plutes

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    Mar 4, 2021
  13. Alec_t

    Alec_t

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    Each dish would need to have a diameter of several wavelengths to be really effective. One wavelength at 120MHz ~= 2.5 metres !!
     
    davenn likes this.
  14. plutes

    plutes

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    Mar 4, 2021
    I just read something along them lines, so does that mean if they were the size of a soccer ball cut in half, it would be in the ghz range?
     
    Last edited: Mar 15, 2021
  15. plutes

    plutes

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    Mar 4, 2021
    [​IMG]
     
  16. bertus

    bertus Moderator

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  17. plutes

    plutes

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    Mar 4, 2021
  18. Technomaniac

    Technomaniac

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    A parabolic dish will be very directional. When I was an apprentice we made a discone for testing customers transceivers. It was made from an old automotive piston drilled for aluminium tubing radials.. For customers' base stations we made coaxial dipoles, a mobile whip over a piece of two inch diameter aluminium tubing. Normally we would use an S.W.R meter for tuning aerials, but I bought an antenna impedance meter which was very handy, and saved the aerials from being trimmed shorter than the ideal length. With multichannel CB radios, one could look at the SWR at both ends of the band and know whether the aerial was too long or too short.
     
  19. plutes

    plutes

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    Mar 4, 2021
    I ended up making a dipole out of a spare bit of coax, and to be fair it out performed my expectations. My thought was to have 5 parabolic dishes covering more area, more skin contact in the game but looking into the math it just gives me a headache.

    My radio setup is basic a handheld tti scanner, and a nooelec sdr, if I can get permissions for a discone mounted as high as possible I will have to upgrade to a base station, then start experimenting with aerials.
     
  20. Technomaniac

    Technomaniac

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    Oct 31, 2020
    You know you can make a coaxial dipole using just coax. Work out your length 1/4 wavelength minus 2 percent, remove the outside insulation to that length, expand the exposed woven braid and turn it inside out so it is over the feeder coming up. Then find an overhang on your building to hang it from.
     
    Martaine2005 likes this.
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