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  • a little trick to straigtening wire is put one end in a vise and the other in a good pair of pliers and pull hard it goes quite strait.
    T-EGLF8

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    • Originally posted by abcd567
      .
      Units of Electricity‏ & Scientists‏


      Sl. No. Unit Name Description Named After Photo
      10 Tesla Magnetic Flux Density (in SI Units) Nikola Tesla- Physicist and Electrical Engineer - Born & grown in Hungary, later became US citizen (18561943)

      .
      Nikola Tesla is born in Smiljan (Croatia) moved to Gospić (Croatia),then Karlovac(Croatia),In 1873 returns to Smiljan. His parents were Serbian. No connection to Hungary in early years.
      Historically he was born in Austrian Empire that exists untill 1867 then it's called Austro-Hungarian Empire, but Nikola is 11 then.

      Sorry for OT.
      Last edited by Amper; 2014-04-07, 17:53.
      For official support use Contact Form

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      • Another project:

        http://ads-b-antenna.blogspot.pt/

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        • .
          TRANSLATION OF SWR INTO MISMATCH LOSS IN dB

          FORMULAE
          Mismatch Loss = - 10 log { 1 - [ (SWR-1)/(SWR+1) ] 2 } dB

          CALCULATED VALUES OF MISMATCH LOSS
          SWR 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 7 8 9 10
          Mismatch Loss dB 0 0.18 0.51 0.88 1.25 1.60 1.94 2.25 2.55 2.83 3.10 3.59 4.03 4.43 4.81

          SWR 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
          Mismatch Loss dB 5.15 5.47 5.76 6.04 6.30 6.55 6.78 7.00 7.21 7.41 7.61 7.79 7.96 8.13 8.3
          .
          Last edited by abcd567; 2014-04-10, 12:00.

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          • swr and loss should never be lumped together.... It easy to rely on a low swr as indication of a "good" antenna and feeder, but this simply is NOT true:-(
            put a 75 Ohm resistor across your receiver... great swr and total loss! ie you'll hear nothing...

            Sent using Tapatalk from my ZX81

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            • a VERY quickly (all of 30mins) made 4 element collinear made with RG59U tied to a wooden stick to keep it strait. I know this is 75ohm cable into something expecting 50ohm's but it hasn't done to bad, no trimming just followed the instructions (it's only on a 1 meter tail)

              colinear.jpg

              the antenna was left open ended. proves that not only are these antenna's easy to make its hard to get them terribly wrong too.
              Last edited by SpaxmoidJAm; 2014-04-10, 11:50.
              T-EGLF8

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              • Originally posted by T-LPPR7 View Post
                I recognise the software from some Google searches for rf software solution someone has access to some good toys, looks to be a bit tricky to copy at home.
                T-EGLF8

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                • Originally posted by Rooster View Post
                  swr and loss should never be lumped together.... It easy to rely on a low swr as indication of a "good" antenna and feeder, but this simply is NOT true:-(
                  put a 75 Ohm resistor across your receiver... great swr and total loss! ie you'll hear nothing...

                  Sent using Tapatalk from my ZX81
                  The word "Loss" here does not mean "wastage" of power, such as power absorbed by a resistor.
                  "Loss" here means "Lack of Full Transfer" of power between Antenna & Transmitter/Receiver.

                  In case of Transmitting Antenna, it is the ratio of power available at Transmitter, to the power transferred to Antenna, expressed in dB.
                  In case of Receiving Antenna, it is the ratio of power available at Antenna, to the power transferred to Receiver, expressed in dB.

                  A 3 dB "Mismatch Loss" means only 1/2 of the power available is transferred between antenna & transmitter/receiver.
                  A 6 dB "Mismatch Loss" means only 1/2 x 1/2 = 1/4 of the power available is transferred between antenna & transmitter/receiver.
                  A 9 dB "Mismatch Loss" means only 1/2 x 1/2 x 1/2 = 1/8 of the power available is transferred between antenna & transmitter/receiver.
                  ......... and so on.

                  For example in case of a 100 watt Transmitter, a mismatch loss of 3dB (SWR = 5.8) means only 1/2 of 100 watts (i.e. 50 watts) are transferred to antenna and radiated.
                  In order to be able to radiate full 100 watts:
                  • Either the impedances of antenna & transmitter are matched
                  OR
                  • A 200 watt transmitter is used to transfer & radiate 100 watts....... a very costly option.



                  In case of a receiver, a mismatch loss of 3 dB (SWR = 5.8) means only half the signal received by antenna is transferred to receiver.
                  This can easily be overcome by using a 3 dB+ pre amplifier, a very cheap and practical solution, as power involved is in micro-watts, and not in hundreds of watts.
                  Last edited by abcd567; 2014-04-10, 13:03.

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                  • true, but I honestly think all this techno mumbo jumbo is massive overkill... I suspect most users just want to build a working antenna.. the maths just complicates folk to the point of giving up before they start.

                    Sent using Tapatalk from my ZX81

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                    • Originally posted by Rooster View Post
                      true, but I honestly think all this techno mumbo jumbo is massive overkill... I suspect most users just want to build a working antenna.. the maths just complicates folk to the point of giving up before they start.

                      Sent using Tapatalk from my ZX81
                      Agreed - could the relevant bits be extracted and put into threads - "best antenna - coco with no amplifier", "best antenna - coco with amplifier" and "best antenna for use in a hi-rise window"

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                      • Originally posted by peterhr View Post
                        Agreed - could the relevant bits be extracted and put into threads - "best antenna - coco with no amplifier", "best antenna - coco with amplifier" and "best antenna for use in a hi-rise window"
                        Yes, BUT, people need ot understand that even with a great antenna if you pair it up with cheap coax and/or a long length of it, it will really impact your reception. When I had my DVB-T dongle up with a good antenna it had a fairly long run of coax. I was only hearing planes out to about 350 km, even with the FR24 receiver. When I installed the FR24 receiver on the permanent antenna with a shorter run of coax the reception distance increased to approximately 500 km. That is a major improvement.

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                        • Originally posted by Rooster View Post
                          true, but I honestly think all this techno mumbo jumbo is massive overkill... I suspect most users just want to build a working antenna.. the maths just complicates folk to the point of giving up before they start.

                          Sent using Tapatalk from my ZX81
                          Originally posted by peterhr View Post
                          Agreed - could the relevant bits be extracted and put into threads - "best antenna - coco with no amplifier", "best antenna - coco with amplifier" and "best antenna for use in a hi-rise window"
                          Originally posted by HighlyCool View Post
                          Yes, BUT, people need ot understand that even with a great antenna if you pair it up with cheap coax and/or a long length of it, it will really impact your reception. When I had my DVB-T dongle up with a good antenna it had a fairly long run of coax. I was only hearing planes out to about 350 km, even with the FR24 receiver. When I installed the FR24 receiver on the permanent antenna with a shorter run of coax the reception distance increased to approximately 500 km. That is a major improvement.

                          You are right. That is what I have been trying to tell from beginning.
                          For ADS-B Reception, we have a RECEIVING antenna, so all this stuff of SWR, Antenna Gain, Coax Attenuation etc are not as critical as in case of TRANSMITTING antennas.

                          All losses caused by:
                          • Low Gain Antenna (poor design, wrong velocity factor / dimensions, poor workmanship, etc).
                          • Impedance mismatch / high SWR.
                          • Attenuation caused by cheap / long coaxial cable.

                          can easily be overcome by using a very cheap method: an in-Line Amplifier.

                          I have practically demonstrated that use of Amplifier successfully overcomes all these and I have achieved good coverage/range only because of use of Amplifier.

                          All technical formulas & calculations I post are intended for use by technically advanced members, and not to discourage the Novice.

                          For Novice I will say "Built any antenna, and if you don't get good results, don't get discouraged. Simply add an Amplifier, the easiest solution for Novice. Then try other more difficult solutions like changing location/height of antenna, using a better designed, well built antenna, use a shorter length of coax etc etc
                          Last edited by abcd567; 2014-04-10, 14:09.

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                          • Originally posted by HighlyCool View Post
                            Yes, BUT, people need ot understand that even with a great antenna if you pair it up with cheap coax and/or a long length of it, it will really impact your reception. When I had my DVB-T dongle up with a good antenna it had a fairly long run of coax. I was only hearing planes out to about 350 km, even with the FR24 receiver. When I installed the FR24 receiver on the permanent antenna with a shorter run of coax the reception distance increased to approximately 500 km. That is a major improvement.
                            The FR24 Receiver's built-in RF pre-Amplifier stage is much more powerful than the RF stage of DVB-T USB Dongle, a better FR24 antenna & a better coax, and hence combined effect is a larger range.
                            That is why DVB-T + Home made Antenna + Ordinary Coax needs an external in-Line Amplifier to compensate for it's poor RF pre-amplifier stage & poor antenna & cable losses.
                            Last edited by abcd567; 2014-04-10, 14:25.

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                            • Originally posted by SpaxmoidJAm View Post
                              a VERY quickly (all of 30mins) made 4 element collinear made with RG59U tied to a wooden stick to keep it strait. I know this is 75ohm cable into something expecting 50ohm's but it hasn't done to bad, no trimming just followed the instructions (it's only on a 1 meter tail)

                              [ATTACH=CONFIG]3852[/ATTACH]

                              the antenna was left open ended. proves that not only are these antenna's easy to make its hard to get them terribly wrong too.
                              With 50 Ohm apparatus connected to 75 Ohm Coaxial Cable & 75 Ohm Coaxial Collinear Antenna, the mismatch causes negligible loss. Please see calculations below:

                              Reflection Coefficient Γ = (Z1 - Z2) / (Z1 + Z2) = (75-50)/(75+50) = 0.2
                              SWR = (1+Γ)/(1-Γ) = (1+0.2)/(1-0.2) = 1.5

                              Don't get terrified by 1.5 SWR ...
                              The Mismatch Loss in dB = -10 log(1 - Γ2) = -10 log (1-0.2 2) = -10 x -0.01773 = 0.1773 dB .... peanuts

                              The mismatch loss can also be calculated directly using SWR by following formula:
                              Mismatch loss in dB = -10 log {1 - [(SWR-1) / (SWR+1) ]2 }
                              Last edited by abcd567; 2014-04-10, 14:53.

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                              • Originally posted by abcd567 View Post
                                The FR24 Receiver's built-in RF pre-Amplifier stage is much more powerful than the RF stage of DVB-T USB Dongle, a better FR24 antenna & a better coax, and hence combined effect is a larger range.
                                That is why DVB-T + Home made Antenna + Ordinary Coax needs an external in-Line Amplifier to compensate for it's poor RF pre-amplifier stage & poor antenna & cable losses.
                                I was seeing similar results on the long run of coax with both the DVB-T dongle and the FR24. The preamp doesn't do much good once you have lost the signal coming down the line. An amplifier should be mounted as close to the receiving antenna as possible so you still have a good signal and can boost it going into the longer run of coax toward the receiver.

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