Announcement

Collapse
No announcement yet.

best antenna

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Would a capacitor work where the two halves are soldered, so an amp could be used?

    Sent from my Nexus 4 using Tapatalk

    Comment


    • Originally posted by peterhr View Post
      Would a capacitor work where the two halves are soldered, so an amp could be used?

      Sent from my Nexus 4 using Tapatalk
      I am not sure, as I have not tried it.
      This proposal is similar to inserting a capacitor at shorted top of CoCo, proposed by you earlier.
      Both seem to be good idea, but the capacitor has to be weather-proof type (or inside a weather-proof housing) if antenna is installed outdoors.

      Both proposals need to be tried.
      If this works, then there will be no need to insert a DC blocking capacitor between amplifier & antenna.

      Comment


      • Originally posted by peterhr View Post
        12v worked for me - I'm not sure going to 15v made much difference (could be dependent on the amp)
        12v did work for me too. I tested a three part Coco shorted and got a max distance of 360km. The antenna was outside but not above roof height but still i had a clear view looking South and East. So for me shorted is a better option than whipped.

        Comment


        • Originally posted by mickopla View Post
          12v did work for me too. I tested a three part Coco shorted and got a max distance of 360km. The antenna was outside but not above roof height but still i had a clear view looking South and East. So for me shorted is a better option than whipped.
          My trial runs also show that CoCo with shorted top is better than unshorted whiped one.

          I undersand that FR24 supplid antenna also has the core shorted to braid at top. Those who have FR24 supplied antnna can test this by checking the continuity using a multimeter.



          Sent from my N762 using Tapatalk 2
          Last edited by abcd567; 2014-01-02, 22:42.

          Comment


          • Originally posted by peterhr View Post
            Would a capacitor work where the two halves are soldered, so an amp could be used?

            Sent from my Nexus 4 using Tapatalk
            Considering the theory of stubs, it appears that inserting a capacitor right in the middle of a stub may disturb stub's impedance matching function. This however requires further study. Initial study of stub theory is given below:

            "In radio-frequency engineering, a stub is a length of transmission line that is connected at one end only. The free end of the stub is either left open-circuit or short-circuited. Neglecting transmission line losses, the input impedance of the stub is purely reactive; either capacitive or inductive, depending on the electrical length of the stub, and on whether it is open or short circuit. Stubs may thus be considered to be length-dependent capacitors and length-dependent inductors.

            Because stubs take on reactive properties as a function of their electrical length, stubs are most common in UHF or microwave circuits where the line lengths are more manageable. Stubs are commonly used in antenna impedance matching circuits.

            Resonant stub
            Stubs are often used as resonant circuits. A stub of length L will have a capacitive impedance when L< 1/4 wavelength, and inductive impedance when L>1/4 wavelength. At precisely L = 1/4 wavelength the stub presents a short circuit. This is qualitatively the same behavior as a series resonant circuit.

            When the L>1/4 wavelength, the impedance will become inductive and start increasing with the length of stub. The impedance will rise until the point where L = 1/2 wavelength, at which point it will be infinity i.e. open circuit. After this point (which is actually an anti-resonance point) the impedance will again become capacitive and start to fall. It will continue to fall until at L = 3/4 wavelength it again presents a short circuit. This response of the stub continues to repeat with increasing length, alternating between resonance and anti-resonance."


            The Practical Approach: On a second thought, why to break our heads with theory? Insert a capacitor where the two halves are soldered, give the antenna a trial run, and we will know the answer!
            .

            .
            Last edited by abcd567; 2014-01-03, 09:58.

            Comment


            • Originally posted by peterhr View Post
              Would a capacitor work where the two halves are soldered, so an amp could be used?

              Sent from my Nexus 4 using Tapatalk
              I have now un-soldered the joint of two-halves of the antenna, making the 1/4 wavelength stub open-circuited, and have put the antenna on trial run for next 24 hrs. I will post the results when trial run is complete.

              Please see explaination below:


              Earlier I have used a 1/4 wavelength stub for impedance matching. This stub was short-circuited at one end.

              Further study showed that open-ended stub can also be used for impedance matching.

              For Transmitting Antennas, a short-circuit-ended stub is preferred as it has less radiation from the ends, while for an open-ended stub, it is difficult to make a perfect non-radiating open circuit as there are always some end effects on the stub. Also, there is a voltage maximum at an open circuit. As the transmitter feeds a large amount of power to the antenna, the open-end voltage is high, and may result in spark, leading to electrical safety problems.

              For Receiving Antennas, there is no high power signal fed to antenna and open-ended stub should not pose any of the above two problems. For receiving purposes, the open-ended stub may prove as good as a short-circuited stub.
              Last edited by abcd567; 2014-01-03, 21:35.

              Comment


              • See pictures below for coverage of a Franklin antenna with OPEN ENDED 1/4 wavelength Stub

                franklin+impedance-matching-OPEN-stub.jpg . DSC03035R.jpg

                .
                Last edited by abcd567; 2014-01-07, 17:49.

                Comment


                • Originally posted by abcd567 View Post
                  See pictures below for coverage of a Franklin antenna with OPEN ENDED 1/4 wavelength Stub

                  [ATTACH=CONFIG]3169[/ATTACH] . [ATTACH=CONFIG]3168[/ATTACH]

                  .
                  In general with your testing what percentage gain do you think your height on the 8th floor would have over a normal two storey roof height Antenna?

                  Comment


                  • Originally posted by mickopla View Post
                    In general with your testing what percentage gain do you think your height on the 8th floor would have over a normal two storey roof height Antenna?
                    That's a good question and there's a simple answer. Elevation wont increase the gain of an antenna one iota. If an antenna is held in the hand standing on a biscuit tin at ground level it will still have the same gain as if it were at an elevation of 100ft. What elevation will hopefully give you is better coverage, as height (in theory) gives you clearance from obstacles. But (and there's always a but) as you increase the height of your antenna you also increase the length of cable which increases the losses. So it's the cable type which is just as important as the antenna 'gain' as you increase the height.

                    In short, clearance from obstacles and a good low loss cable is just as important as anything else when it comes to antennas.

                    Hope this helps,
                    Regards,
                    Gregg
                    Last edited by fungus; 2014-01-07, 22:27.
                    YSSY2/T-YSSY4 [SBS-1 Basestation w/- SSE-1090 SJ Mk2 Antenna (Thanks Delcomp) ] [Uniden UBCD996T w/- 16 element Wideband Discone VHF/UHF Antenna, and tuned 108MHz-137MHz Airband Antenna] [Trialing a home-brew 1090MHz collinear antenna]

                    Comment


                    • Originally posted by mickopla View Post
                      In general with your testing what percentage gain do you think your height on the 8th floor would have over a normal two storey roof height Antenna?
                      Height of antenna does not affect gain or coverage. It only helps to overcome the affect of any tall object obstructing the signal. If there are no obstruction, a 2 story high antenna is as good as 8 story high antenna.

                      In my range plots of adsbScope, you will notice several sharp reductions in range in many directions, although it is same antenna at same height.

                      The sharp reductions in range are in those directions where there are other tall buildings surrounding my building.

                      If there were no tall buildings around my building, the range curve would be almost a perfect circle.

                      Since your anrenna is higher than all other buildings/houses around your house, further increasing antenna height is not going to give you any increase in range.
                      Last edited by abcd567; 2014-01-07, 23:03.

                      Comment


                      • Thanks guys for the replies. The explanations i was expecting with advantage of height that it clears obstructions hence gaining range. There is a local FR24 feeder F-EIWF1 who has his Antenna on top of a mountain and his range is excellent. Before i knew his location i was baffled to why he had such good range but when i found out his Antenna was on a mountain top it all became clear

                        Comment


                        • Originally posted by mickopla View Post
                          Thanks guys for the replies. The explanations i was expecting with advantage of height that it clears obstructions hence gaining range. There is a local FR24 feeder F-EIWF1 who has his Antenna on top of a mountain and his range is excellent. Before i knew his location i was baffled to why he had such good range but when i found out his Antenna was on a mountain top it all became clear
                          Even with antenna at hill-top, his range wont exceed 500km due to curvature of earth, but within this 500km radius, he will have full, unobstructed coveage of all aeroplanes.

                          Sent from my N762 using Tapatalk 2

                          Comment


                          • Originally posted by abcd567 View Post
                            Height of antenna does not affect gain or coverage. It only helps to overcome the affect of any tall object obstructing the signal. If there are no obstruction, a 2 story high antenna is as good as 8 story high antenna.

                            In my range plots of adsbScope, you will notice several sharp reductions in range in many directions, although it is same antenna at same height.

                            The sharp reductions in range are in those directions where there are other tall buildings surrounding my building.

                            If there were no tall buildings around my building, the range curve would be almost a perfect circle.

                            Since your anrenna is higher than all other buildings/houses around your house, further increasing antenna height is not going to give you any increase in range.
                            I cant say I agree there on the point you make about increasing the antenna height not increasing range or coverage. I've proved it myself with my setup. I think you are getting mixed up between range and gain. It wont help gain but sure helps range to increase the antenna height, although due to the curvature of the earth and physical limitations in height etc you will inevitably hit a 'ceiling' which you've rightly pointed out in a later post. I've more than doubled my coverage (the total number of aircraft I can 'see' at any given time) and increased the range of my receiver by a good 50nm by simply increasing the height of the antenna and improving the cable. Obviously what you say about obstructions is correct, that's a different issue. If some one is already cleared of obstructions, adding height wont affect that.

                            Regards,
                            Gregg
                            Last edited by fungus; 2014-01-08, 00:09.
                            YSSY2/T-YSSY4 [SBS-1 Basestation w/- SSE-1090 SJ Mk2 Antenna (Thanks Delcomp) ] [Uniden UBCD996T w/- 16 element Wideband Discone VHF/UHF Antenna, and tuned 108MHz-137MHz Airband Antenna] [Trialing a home-brew 1090MHz collinear antenna]

                            Comment


                            • Having the antenna behind glass will reduce signal considerably though, won't it?

                              Sent from my Nexus 4 using Tapatalk

                              Comment


                              • Originally posted by peterhr View Post
                                Having the antenna behind glass will reduce signal considerably though, won't it?

                                Sent from my Nexus 4 using Tapatalk
                                Certainly not something I'm familiar with but from what I'm reading on the net the short answer seems to be no.
                                The problem begins though if you have that window tint film on the glass. Some are metallic based and can affect signal strength through it.

                                Regards,
                                Gregg
                                Last edited by fungus; 2014-01-08, 00:04.
                                YSSY2/T-YSSY4 [SBS-1 Basestation w/- SSE-1090 SJ Mk2 Antenna (Thanks Delcomp) ] [Uniden UBCD996T w/- 16 element Wideband Discone VHF/UHF Antenna, and tuned 108MHz-137MHz Airband Antenna] [Trialing a home-brew 1090MHz collinear antenna]

                                Comment

                                Working...
                                X