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  • Good Day everyone.

    I found something quite interesting. A few months back, I built a CoCo out of LMR-400. I precisely cut my coax, including VF measurements, and sealed everything up inside a fiberglass tube.

    I installed this antenna onto a small satellite dish foot screwed to my wooden fence, due to it being winter in Minnesota.

    I live 5 miles from MSP (bearing 230), and 3.5 miles from STP (bearing 85) airports. MSP is our main international airport, and STP is a rather busy business / Army Aviation airport.

    This feeder was using a Raspberry Pi with a generic RTL-SDR R820T tuner. the base of the antenna was maybe 5' above the ground, 5' away from my house on the south side. 20' of Belden 9913F7 connects the antenna to the RTL.
    A 10 day average from this installation yielded 25,000 positions, with 530 unique aircraft seen.

    Once the weather got nicer, I moved this antenna to the top of a mast on a tripod on my roof.

    The same antenna was installed, with the same coax feedline to my feeder. The antenna is now at 25' AGL. I upgraded to a Raspberry Pi 2, and a Nooelec R8020T2 with TCXO.

    My averages have dropped from 25000 to 10,000 positions reported. Same antenna, same coax, 20' higher, on a post in clear space.
    Any idea why this might have happened?

    Comment


    • Originally posted by zryder94 View Post
      Good Day everyone.

      I found something quite interesting. A few months back, I built a CoCo out of LMR-400. I precisely cut my coax, including VF measurements, and sealed everything up inside a fiberglass tube.

      I installed this antenna onto a small satellite dish foot screwed to my wooden fence, due to it being winter in Minnesota.

      I live 5 miles from MSP (bearing 230), and 3.5 miles from STP (bearing 85) airports. MSP is our main international airport, and STP is a rather busy business / Army Aviation airport.

      This feeder was using a Raspberry Pi with a generic RTL-SDR R820T tuner. the base of the antenna was maybe 5' above the ground, 5' away from my house on the south side. 20' of Belden 9913F7 connects the antenna to the RTL.
      A 10 day average from this installation yielded 25,000 positions, with 530 unique aircraft seen.

      Once the weather got nicer, I moved this antenna to the top of a mast on a tripod on my roof.

      The same antenna was installed, with the same coax feedline to my feeder. The antenna is now at 25' AGL. I upgraded to a Raspberry Pi 2, and a Nooelec R8020T2 with TCXO.

      My averages have dropped from 25000 to 10,000 positions reported. Same antenna, same coax, 20' higher, on a post in clear space.
      Any idea why this might have happened?
      Is the length of Coax between Antenna & DVB-T Dongle (R8020T2) same as before?
      If is now longer, then how many feets longer? What type of Coax?
      Possibly the drop in positions reported is due to the attenuation (loss of signal) in long length of Coax.

      Comment


      • Originally posted by abcd567 View Post
        Is the length of Coax between Antenna & DVB-T Dongle (R8020T2) same as before?
        If is now longer, then how many feets longer? What type of Coax?
        Possibly the drop in positions reported is due to the attenuation (loss of signal) in long length of Coax.
        Same piece of coax. Same length. The coax is Belden 9913F7, so the loss should be quite inconsequential. The only difference is the old tuner had a piece of coax soldered directly to the connector, with a SO-239 connector. The new one uses an MCX to SMA adapter cable, with an SMA to SO-239 adapter in line.

        I was planning on swapping out the tuners to experiment, but those connectors should have negligible loss.

        Comment


        • Interestingly enough, I swapped out my RTL with R8020T2 TCXO dongle with its MCX-SMA cable, SMA to SO-239 adapter for my older R8020T dongle with a hardwired cable with an SO-239 adapter, and my positions reported by FlightAware increased from 400 positions to 2184 positions the following hour.

          I wonder if its the dongle or the adapters. Time to break out the soldering iron to find out!

          Comment


          • Originally posted by abcd567 View Post
            Add a 1/4 wavelength (i.e. 1/2 x 117 mm = 58.5 mm) at top of your 9-section CoCo.
            Do Not short the top section. Do not add a resistor.
            Thanks Rooster and abcd567 for your assistance.

            From what you have described, I'm should discard the top (ninth) 117mm piece of LMR400 and replace it with a piece 175.5mm long. Then strip off 58.5mm of the outer jacket, shield and dielectric insulator, which will leave a quarter wavelength of centre core sitting proud on the top of the nine segments of 117mm lengths. Have I got that right?

            I'm planning to use an Elad A12-1090 preamplifier which sounds like should work well from your description.

            Thanks again.

            Comment


            • ...My averages have dropped from 25000 to 10,000 positions reported. Same antenna, same coax, 20' higher, on a post in clear space.
              Any idea why this might have happened?
              Yes, you are further from the ground !!!! COCO's are an omnidirectional antenna... but require a "ground" - this is usually provided by either a ground plane (a sheet of metal - could be your car !) or an identical "antenna" attached to the other half of the feeder (forming a dipole)

              Unless you are up high (geographically) then raising the antenna will lower its pattern... ie it sees less of the sky.
              Provide your antenna with some 1/4 wave radials, and see it sing !

              Comment


              • Originally posted by Avsec View Post
                Thanks Rooster and abcd567 for your assistance.

                From what you have described, I'm should discard the top (ninth) 117mm piece of LMR400 and replace it with a piece 175.5mm long. Then strip off 58.5mm of the outer jacket, shield and dielectric insulator, which will leave a quarter wavelength of centre core sitting proud on the top of the nine segments of 117mm lengths. Have I got that right?

                I'm planning to use an Elad A12-1090 preamplifier which sounds like should work well from your description.

                Thanks again.
                No you did not get it right. What you have described is adding a Whip.
                What I described was adding a 10th section, full coax, identical to the other 9 sections, except that it's length should not be 117mm, but half of it i.e. 58.5mm.

                Alternatively instead of adding 10th section, simply chop-off half of the top 9th section, making top 9th section 58.5 mm long instead of 117mm long.

                Comment


                • Originally posted by abcd567 View Post
                  What I described was adding a 10th section, full coax, identical to the other 9 sections, except that it's length should not be 117mm, but half of it i.e. 58.5mm.
                  Gotcha yer!

                  Thanks again.

                  Comment


                  • SIX LEG SPIDER
                    USES ONLY F-TYPE BARREL CONNECTOR (With Nut & Washer)



                    NO SOLDERING REQUIRED
                    NO SO-239, BNC or N CONNECTOR REQUIRED.



                    FINISHED LENGTHS
                    WHIP: From top of F-connector to top of whip = 69 mm

                    RADIALS: From Point of bending down to tip of radial = 69 mm

                    RADIALS BENDING DOWN: About 45 degrees below horizontal

                    WIRE DIA: Flexible. In this demo core wire of RG6 coax cable is used which has a dia of 1 mm (18 AWG), but wires with bigger dia can as well be used.


                    STEP-1



                    STEP-2



                    STEP-3



                    ON TRIAL RUN



                    DIRECTLY BUILT ON AN AMPLIFIER, INSTEAD OF F-BARREL CONNECTOR

                    Last edited by abcd567; 2015-06-03, 20:16.

                    Comment


                    • You are FANTASTIC !

                      Soon, you can set up a " Museum of 1090 Mhz Homebrew Antenna ".
                      F-WSSS1 - Cats refused to Pee & Pooh on RadarBox - Running a FR24 Receiver & DVB-T Dongle 24/7 to piss off The Chief Thief.

                      Comment


                      • FRANKLIN COLLINEAR ANTENNA - EXPLAINED BY IT's INVENTOR

                        To read the text, click on images to see larger size
                        (or better right click and then choose "Open Link in New Tab").

                        Start reading from "Complete Specifications" at bottom of page 1.


                        . . .
                        Last edited by abcd567; 2015-06-03, 20:21.

                        Comment


                        • Would you guys recommend running two coax cables through a spiral conduit both carrying signal from ADS-B antennas.
                          ex-NZAL1

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                          • shouldn't be an issue at all to run two coaxes side by side.
                            T-EGLF8

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                            • not suitable to be used outdoor..fragile,right?

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                              • Originally posted by kucengemok View Post
                                not suitable to be used outdoor..fragile,right?
                                What isnt ?

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