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Thread: best antenna

  1. #1281
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    Hello, someone can tell me what amplifier serves to 1090mhz?
    Thank you

  2. #1282
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    That would be an Satellite dish LNB amplifier like this one http://www.ebay.co.uk/itm/350657754545

    A satellite receiver passes 13v - 19v up the wire to the LNB (Low Noise Block) mounted on the dish. 13v says please receive vertically polarised signals, 19v horizontal signals. In addition the receiver will put a 22Khz audio signal up the wire to tell the LNB to switch to hi-band. Now these amplifiers are designed to work in that environment - so we need to put 15v-18v up the wire to run the amplifier, and the amplifier will pass that voltage on to run the LNB. We can't just connect the supply to the coax since it will also pass the power back down to the dongle and it won't like it. We might also have to protect the antenna from the voltage that would go to the LNB.

    So,

    we need a line power inserter to add power to the coax http://www.ebay.co.uk/itm/161044085914 - but not to pass it to the dongle ... and a 15v-18v power supply http://www.ebay.co.uk/itm/120976304351 (may need work to make the plugs fit????)

    we may need a DC voltage blocker http://www.ebay.co.uk/itm/171258939281 if our antenna presents a resistance to a DC test.
    Last edited by peterhr; 2014-07-21 at 18:35.

  3. #1283
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    Towards the end of last year, I got an Antenna Manufacturer to build me a 1090 mHz antenna. Paid a small fortune for the darn thing, but was promised at least 9dB gain with it. Had it up and down a few times, never could quite get proper reception with it, so summised it might got damaged in transit, maybe just a bad connection or something, as the N connector at the bottom did not feel proper.
    Today I took it down, opened the top end and tested for continuity.

    From N-connector at the base: From centre to top centre element - No continuity.
    From N-connector at the base: From outer to top centre element - Continuity. This did not seem right, as I expected centre to top to give a result.

    So I took the thing apart. Using destructive means, as I could not undo it any other way.
    Eureka! This aint a colinnear antenna... its a J-pole. Another moment!

    Read up on J-poles tonight... not much the wiser, to be quite honest. Discovered this might be a Super J-pole. Now since I never got any decent reception with this thing (with or without the amplifier), was it a case of maybe a bad antenna, or maybe me not wiring it correctly, or just a flawed design/construction? I cant understand how this works, or why a J-pole would be better than a collinear. I cant see the active part that picks up a signal, as its basically a short, with the inner and outer of the cable connected to the same wire... didn't even bother measuring the lenghts of the elements or the coils.

    Those of you with more antenna knowledge, please share your ideas and thoughts on this matter.

    jpole2.jpg
    Last edited by HermanZA; 2014-07-21 at 21:52.

  4. #1284
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    Quote Originally Posted by abcd567 View Post
    It just occurred to me that coaxial collinear antenna made of coaxial cable is a compromise.

    For any element of the coco, the central conductor is used for phasing & should be 1/2 wavelength.
    As the phasing function is carried out by inner space of the coaxial where the electromagnetic field is totally confined in the dielectric between core & shield, the required length is 1/2 wavelength in air (138 mm) x Velocity factor of the dielectric. If VF is 0.85, the length should be 117mm

    The outer surface of the shield of that very element is used for receiving the incoming electromagnetic field. Its length should also be 1/2 wavelength. Since the incoming field is totally in the space between antenna & aircraft, and is in air, Velocity factor is 1. Hence the length should be 1/2 wavelength in air = 138mm.

    We are making CoCos with element length using Velocity factor of Coaxial Cable. This makes the phasing element (inner space) accurately dimensioned (117mm), but makes the receiving element (outer surface of shield) shorter than optimum (117mm instead of required 138mm).

    The CoCo will be precise & optimum only if inside dielectric is air.
    If the elements are made of hollow metallic tube with central conductor supported by few rings/washers of plastic or rubber, this can be achieved.

    Attachment 4420

    .
    Don't be too despondent F-EGLF1 has been doing practical lab tests on built antennas and has shown that your calculations can't be too far off. The results prove the theory. If theory was the end result - we would had the Higgs-Boson long ago.

  5. #1285
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    Quote Originally Posted by HermanZA View Post
    Read up on J-poles tonight... not much the wiser, to be quite honest. Discovered this might be a Super J-pole. Now since I never got any decent reception with this thing (with or without the amplifier), was it a case of maybe a bad antenna, or maybe me not wiring it correctly, or just a flawed design/construction? I cant understand how this works, or why a J-pole would be better than a collinear. I cant see the active part that picks up a signal, as its basically a short, with the inner and outer of the cable connected to the same wire... didn't even bother measuring the lenghts of the elements or the coils.

    Those of you with more antenna knowledge, please share your ideas and thoughts on this matter.

    jpole2.jpg
    Hi Herman,
    The first antenna I built was a J pole. Don't ask me how they work though! Yours looks pretty similar to mine but I didn't have the coils at the top of the long part. Can you measure the lengths of the 2 parts and also the distance from the base to where the coax is attached. Also which side the centre core of the coax is attached to (long or short side).

    Cheers
    Trig

  6. #1286
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    Quote Originally Posted by peterhr View Post
    Don't be too despondent F-EGLF1 has been doing practical lab tests on built antennas and has shown that your calculations can't be too far off. The results prove the theory. If theory was the end result - we would had the Higgs-Boson long ago.
    I have a bitter experience of CoCos. I have noticed that like me, many other amateurs have experienced unsatisfactory performance from their CoCos

    I have built more than 6 different CoCos. Some were better than others, but all have miserably failed when compared to other antennas I have built (like simplest 1/2 wavelength dipole, 4 element Franklin, sleeved dipole). I fail to understand why my CoCos don't perform as they should. Is it using low cost cable like RG6, or bad workmanship, or wrong design/dimensions? Is it due to combination of many small factors, or is it one major factor?

  7. #1287
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    How about going for a franklin concept whip with a J at the bottom for impedance matching. Should be able to do something that is robust enough to be self supporting or be able to be supported from a fibreglass rod with 100 - 150 mm standoff's crucially placed zero voltage positions.

    That should eliminate all velocity factors from the calculations.

    With my antenna I did place the amplifier at the base of the antenna (ratrher than in line) as much as anythinr to reduce impedance mis-match issues. I'm running with RG6 and I'm getting about as much distance as I could hope for with a dongle - 450km in the good directions with no hills.
    Last edited by peterhr; 2014-07-22 at 19:06.

  8. #1288
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    Hello everyone

    Just curious

    The small outdoor antenna for DVB-T signal can capture?

    Type this

    http://www.microcubo.com/fotos_produ...ster.1.big.jpg

    http://www.ebay.com/itm/Active-DVB-T...item4ad7ec5f52

    http://www.tv-alvitecnica.com/WebRoo...geImg.asp.jpeg

    Or all antennas even those are limited to 860MHz capture 1090mhz?

    Thanks

  9. #1289
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    Quote Originally Posted by peterhr View Post
    How about going for a franklin concept whip with a J at the bottom for impedance matching. Should be able to do something that is robust enough to be self supporting or be able to be supported from a fibreglass rod with 100 - 150 mm standoff's crucially placed zero voltage positions.......
    J-Pole is a monopole+matching stub minus ground-plane. Performance of any monopole/whip without ground plane is inferior to a dipole or a monopole+groundplane.
    Last edited by abcd567; 2014-07-22 at 20:08.

  10. #1290
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    Quote Originally Posted by ptruicp View Post
    Hello everyone

    Just curious

    The small outdoor antenna for DVB-T signal can capture?

    Type this

    http://www.microcubo.com/fotos_produ...ster.1.big.jpg

    http://www.ebay.com/itm/Active-DVB-T...item4ad7ec5f52

    http://www.tv-alvitecnica.com/WebRoo...geImg.asp.jpeg

    Or all antennas even those are limited to 860MHz capture 1090mhz?

    Thanks
    They probably wouldn't perform anything like as well as a tuned antenna at the right frequency

    Quote Originally Posted by abcd567 View Post
    J-Pole is a monopole+matching stub minus ground-plane. Performance of any monopole/whip without ground plane is inferior to a dipole or monopole+groundplane.
    OK, add a [psudo] groundplane - I was just thinking of something that is essentially supported from the bottom (ie on a stick)

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