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  • Originally posted by peterhr View Post
    Great offer ... If your able could you do a kit for the coco with instructions on how to cut the cable & assemble, and tell people what pipe to get from - say - wickes.co.uk to put it in to get a nicely tuned antenna (do make a charge to cover costs and handling at least).
    Thanks for the positive feedback !
    Heres what I am getting from a non laser cut coco, mounted at gutter height, not in the clear... the white circles are at 25 miles, so nearly 200 miles coverage.
    Im very pleased with its performance.
    Clipboard01.jpg

    Comment


    • Hi Rooster,

      (Tongue in cheek) The topic heading is "Best Antenna". This thread could run for ever .....

      Trig
      T-EGUB1

      Comment


      • Originally posted by Rooster View Post
        I honestly, hand on heart feel this is getting silly BIG time now, the thread was for MAKING an antenna to get you going wasn't it ?
        Here we are using a caesium calibrated nuclear powered virtual sledgehammer to crack a non existent nut !!!!!

        All you need to know is some simple maths, and the velocity factor of the cable you are using (varies from type to type of cable AS WELL as manufacturer) then crack on !

        My cable was bought from a satellite dish company - even they didn't know the VF, so I dusted off my antenna analyser and ten minutes later we have the number.
        But I am an anal amateur radio enthusiast... I enjoy the challenge of it "being right" - most folk just want it to work, and a coat hanger will receive something !!!!!!!!! If you don't get the technicals down to 0.00000001% IT DOESN'T MATTER it WILL work in some usable way.
        If anyone in the UK want me to send you some cable with all the maths, or even a kit ;-)

        Just crack on lads...
        Thanks for your offer. Sure majority of enthusiast will welcome such a kit with instructions. Your kit & instructions will be very valuable for them.

        Since a vast majority of amateurs make CoCo from RG6, and most use assumed velocity factors (few have Network Analyzer), there is an error in element length.
        As shown in my frequency vs. Gain plot for error in length, if the antenna was cut precisely, it will give 7.5 dB gain. The 1mm short antenna still gives 4.5 dB Gain at 1090 Mhz and will perform ok. It is the optimization which is being sought. The study highlights the impact of error on performance, encouraging amateurs to take more care in determining VF & in cutting/assembling the CoCo.
        Last edited by abcd567; 2014-05-20, 18:25.

        Comment


        • Originally posted by abcd567 View Post
          Hi Dave
          The Gain peaked at 1180 Mhz, i.e.the resonant frequency shifted from 1090Mhz to 1180Mhz, a 90Mhz shift just for 1mm error in length.
          .
          I'm amazed at the effect 1mm has. Thanks for all your hard work
          T-EGUB1

          Comment


          • If any admin are reading this, please can you tell me how best to proceed with the kit(s) ?
            Do I need to start another thread, if so where ?

            If anyone is interested in some form of kit, please can you tell me what you would prefer:

            Cable with instructions:
            Precut sections
            Precut and prepared sections
            Ready assembled antenna without tube (as this will vastly increase postage)
            Totally finished and tested antenna...including tube.

            Or any other combination... feedback most welcome.
            Thanks Guys

            Comment


            • Originally posted by trigger View Post
              I'm amazed at the effect 1mm has. Thanks for all your hard work
              The housing has a dramatic effect too, see the analyser plots attached, I started with a calculated 95MM (allowing about .5MM for joints) then I shortened the segments to 93MM but they still need to go shorter, possibly as short as 88-89MM
              This is where theory and practice don't always meet !!!
              image.jpgimage.jpgimage.jpgimage.jpg
              Note, I have not trimmed the top stub yet, I am just trying to get the segments resonant at the right frequency, I am hoping to end up with a reasonably broad dip covering 1080-1100MHz
              The co-ax is RG402 and the housing is 25MM heavy duty white plastic conduit from Screwfix (yes it does pass the microwave test!)
              Unfortunately I only have tomorrow lunch time to tinker as I am away from work till Tuesday, but I will do what I can.
              Ben.

              Nb 1MM change in length shifts the frequency by about 11MHz.
              Last edited by F-EGLF1; 2014-05-20, 20:40. Reason: Put photos into correct order
              FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

              Comment


              • Originally posted by abcd567 View Post

                Franklin 4-element with matching stub.
                [ATTACH=CONFIG]4116[/ATTACH]

                Later Addition: I am also using an in-Line amplifier (RCA D903, Gain 13-18 dB, Freq Range:950-2050 MHz, Max Output 110dBV, Power pass DC 14-18V 25-40mA)
                Any chance I can ask a favour from you?
                I am planning on giving a Franklin a try for FLARM glider detection on 868.3MHz and I was hoping you could have a quick look at my sketch, I think the dimensions are right, but I am not entirely sure about the tapping point on the stub.
                image.jpg
                I will be using it with a satellite amplifier similar to yours, however I have modified it by removing the DC choke on the antennae end so there is no DC pass-through, and I removed the guts of the F-connector at the same end and replaced it with an SMA connector, I have photos of the mod if you want to see them, but they are still on the camera card at the moment.
                Ben.
                FR24 F-EGLF1, Blitzortung station 878, OGN Aldersht2, PilotAware PWAldersht, PlanePlotter M7.

                Comment


                • Originally posted by Rooster View Post
                  If any admin are reading this, please can you tell me how best to proceed with the kit(s) ?
                  Do I need to start another thread, if so where ?

                  If anyone is interested in some form of kit, please can you tell me what you would prefer:

                  Cable with instructions:
                  Precut sections
                  Precut and prepared sections
                  Ready assembled antenna without tube (as this will vastly increase postage)
                  Totally finished and tested antenna...including tube.

                  Or any other combination... feedback most welcome.
                  Thanks Guys
                  I'm not interested in buying - but I am interested that people have the greatest opportunity of success with the kit.

                  I would suggest supply of coax of known quality and VF, and the source of an easy to obtain tube to mount it in, one where the effect on the VF caused by the tube has been taken into account and instructions (with possibly a you-tube) on how to assemble.

                  Most people have no way to work out the VF to get the tuning right - and that is their main hurdle.

                  We need threads for practical antenna designs. Design + amendments on first post by thread originator (go back and edit it), discussions after first post.

                  Comment


                  • Originally posted by F-EGLF1 View Post
                    Any chance I can ask a favour from you?
                    I am planning on giving a Franklin a try for FLARM glider detection on 868.3MHz and I was hoping you could have a quick look at my sketch, I think the dimensions are right, but I am not entirely sure about the tapping point on the stub.
                    [ATTACH=CONFIG]4133[/ATTACH]
                    I will be using it with a satellite amplifier similar to yours, however I have modified it by removing the DC choke on the antennae end so there is no DC pass-through, and I removed the guts of the F-connector at the same end and replaced it with an SMA connector, I have photos of the mod if you want to see them, but they are still on the camera card at the moment.
                    Ben.
                    Hi Ben
                    Right now I am away from my computer (replying by phone). When I return home, I will model & simulate your Franklin to get best tap position, and post the results. 73 de abcd

                    Comment


                    • Originally posted by Rooster View Post
                      I honestly, hand on heart feel this is getting silly BIG time now, the thread was for MAKING an antenna to get you going wasn't it ?
                      Here we are using a caesium calibrated nuclear powered virtual sledgehammer to crack a non existent nut !!!!!

                      All you need to know is some simple maths, and the velocity factor of the cable you are using (varies from type to type of cable AS WELL as manufacturer) then crack on !

                      My cable was bought from a satellite dish company - even they didn't know the VF, so I dusted off my antenna analyser and ten minutes later we have the number.
                      But I am an anal amateur radio enthusiast... I enjoy the challenge of it "being right" - most folk just want it to work, and a coat hanger will receive something !!!!!!!!! If you don't get the technicals down to 0.00000001% IT DOESN'T MATTER it WILL work in some usable way.
                      If anyone in the UK want me to send you some cable with all the maths, or even a kit ;-)

                      Just crack on lads...
                      Well said..
                      afterall, you only need look at discones, they work wonders, mines a diamond, 25 Mhz to 1400Mhz of course it is resonant at a certain freq, mine being 2mtrs for transmit, but I can tell you it works awesome RX'ng from vhf-midband upwards and transmits at vswr 1.3:1 in vhf marine, 1.5:1 at 70cm (440 Mhz for those who have NFI what that means), and even 1.6:1 at UHF CB and in AU thats 476/477 Mhz, sadly I dont have a 1090 Mhz transmitting capable radio to check that but I'm sure it wont matter since it receives perfectly - that said, I did free up that radio, by getting a couple cheap dongles from China, RG6 and building a 6db coco, which to be expected has a greater range (by about 70nm) and at about 15 dollars in total (all cable/PVC/caps), a darn sight cheaper to dedicate than my 170 (1990 price) dollar diamond discone

                      Comment


                      • When I got my first DVB-T dongle last year, I installed driver, rtl1090 & adsbScope on my laptop, put laptop near window and inserted DVB-T dongle, connected stock antenna and was amazed to see planes popup, though hardly up to 50 kms. While I tried to adjust the position of stock antenna, the thin coax got pulled out from antenna base! They did not solder it properly. I could not put back the coax as antenna base was sealed! At the peak of success an anti climax. I did not give up. I stood near window and held the center wire of pigtail between my thumb & forefinger. Bingo! Planes started popping up again, this time over 100 kms! My body made a better antenna than the stock antenna, and without any maths, VF, SWR, Gain dB calculations :-D
                        DSC02173R.jpg
                        Last edited by abcd567; 2014-05-21, 14:39.

                        Comment


                        • Originally posted by abcd567 View Post
                          When I got my first DVB-T dongle last year, I installed driver, rtl1090 & adsbScope on my laptop, put laptop near window and inserted DVB-T dongle, connected stock antenna and was amazed to see planes popup, though hardly up to 50 kms. While I tried to adjust the position of stock antenna, the thin coax got pulled out from antenna base! They did not solder it properly. I could not put back the coax as antenna base was sealed! At the peak of success an anti climax. I did not give up. I stood near window and held the center wire of pigtail between my thumb & forefinger. Bingo! Planes started popping up again, this time over 100 kms! My body made a better antenna than the stock antenna, and without any maths, VF, SWR, Gain dB calculations :-D
                          Great !

                          Continue holding on to that antenna coaxial cable for as long as you can. LOL !
                          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


                          • Originally posted by Birdie View Post
                            Great !

                            Continue holding on to that antenna coaxial cable for as long as you can. LOL !
                            I dont have to, as I believe in Darwin's theory of evolution, so my antennas have evolved. Here are the evolutionary steps
                            1. Stock antenna
                            2. My body
                            3. A piece of wire taped to window glass
                            4. 1/2 wavelength dipole, 75ohms swr=1 gain=2.1 dB
                            5. Four-element Franklin without impedance matching stub.
                            6. Added an in-line amplifier.
                            7. 3.5 element CoCo
                            8. Four element Franklin with Impedance Matching Stub

                            Comment


                            • Good to hear that. Keep it up ! LOL
                              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


                              • GOOD NEWS
                                Couple of months ago I have made 4 CoCos (3.5-elements each) from same reel of coaxial cable. The reason was that I did not know the VF of cable. The element lengths were 11.0cm (VF=80%), 11.3cm (VF=82%), 11.6cm (VF=84%) and 11.9cm (VF=86%). I put them on trial run one by one, each for 48 hours. I found the best result was given by 11.6 cm, indicating that the cable I used has a VF of 84%.

                                Although there was difference in maximum range for these 4 cocos, the difference was never so crazy as my yesterday's simulation of 8-element coco showed. This sharp conflict between simulation & field test kept pinching me, till I decided to re check my simulation thoroughly for any bugs. I checked all geometry & variable entries one by one (like debugging a computer programming code), and finally found a bug. After removing the bug, I ran simulation, and found that the CoCo is not at all so intolerant to errors. I am now posting the screen shots of debugged simulations which show that varying the element length from 134mm to 139mm has moderate effect on both the Gain & SWR.

                                CoCo 8 elements - Dimension Tolerance 1B.jpg . CoCo 8 elements - Dimension Tolerance 2B.png
                                Last edited by abcd567; 2014-05-21, 07:05.

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