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  • Originally posted by joni1101 View Post
    You kept the dielectric on the center conductor. What correction coefficient did you use?
    I applied no correction factor.

    The electromagnetic field of coax is totally enclosed inside the space between core & shield, and this space is totally filled with insulation. The speed of propagation along coax is therefore determined solely by elocity factor of the dielectric material in the coax.

    The antenna wire's electromagnetic field is un-enclosed, and is in a space of which the wire insulation constitutes negligible part (thickness wise). Its Velocity Factor is therefore:

    VFeff = (VF1 x t1 + VF2 x t2) / (t1+t2)
    where
    VF1 is velocity fctor of insulation, say 0.66
    t1 is thickness of insulation say, 2 mm
    VF2 is velocity fctor of air = 1
    t2 is thickness of air say 10 km **

    **The thickness of air in which electromagnetic field of antenna wire exists is the distance between transmitting antenna and the receiving antenna, hence it is in tens or hundreds of kilometers.

    Hence VFeff = (0.66 x 0.000002 km + 1 x 10 km)/(0.000002 km+10 km) = 10.00000132 / 10.000002 = 1

    Electromagnetic field of Antenna
    Occupies space between transmitting and receiving antennas





    Electromagnetic field of a Coax cable
    Totally confined in the space between core and shield i.e. totally inside the core insulation

    Comment


    • No correction factor required for insulation on Whip
      To verify above statement, I ran analyzer with insulated and bare whips, both 67 mm.

      The test proved that correction factor for insulation is not required.
      Both gave same VSWR (1.4) and both were resonant at same frequency (1090 Mhz).
      Please see photos below:

      Whips
      67mm bare, 67mm insulated, 72mm insulated




      Insulated Whip 67 mm
      VSWR, R, X, Z, S11 at 1090 MHz





      Bare Whip 67 mm
      VSWR, R, X, Z, S11 at 1090 MHz




      Bare Whip 67 mm
      VSWR vs. Frequency sweep, marker at 1090 MHz

      Comment


      • Thank you. Brilliant explanation and great tool you got to analyze antennas. Remember in the stackexhange forum the question on how long to make the sides of the can, whether you subtract the radius of the ground plane from the length of the cab to equal quarter wavelength. BTW in the ham stackexhange forum they wanted reputation score of 15 before you could post because they want to prevent that question from being spammed.

        Sent from my Pixel using Tapatalk

        Comment


        • Do you have some cans with bigger ground plane? Could you try cutting slots into the side of the can to electrically insulate the vertical shield? It's great you have this tool!!

          Sent from my Pixel using Tapatalk

          Comment


          • This type of tools are priced several hundred to several thousand dollars. I found this model for around $180 to $220 on ebay, and then found one seller for $140 on Banggod.com on special offer, so I purchased it from Banggood special offer seller.
            Last edited by abcd567; 2017-01-25, 17:38.

            Comment


            • Originally posted by abcd567 View Post
              There is no easy way to find RF noise except by using costly test equipment.

              Best option is to buy an Orange ProStick and an external Filter.

              First set the gain at 38 dB, and try Orange ProStick alone. Next at same gain setting add the external Filter and try again.

              Compare the two results. It will give you an indication if adding a filter is benefitial or not.

              After finding which is better (with or without filter) adopt that setup. Now set gain at 49.6 dB, then drop down in steps of 3 dB and watching where you get maximum message rate. Generally people get best between 30 dB and 45 dB.
              I have only been online since 11/19/2016. I now use an RPi Jessie with an orange Prostick. I have several questions but my first is how do I set the LNA gain of the Prosick using FR24 software? Under PiAware, rtlsdr-gain is available. Is there a way to install rtlsdr-gain under FR24.

              Thanks
              T-KCLT3 - Raspberry Pi3 Jessie, 8 element collinear indoor antenna

              Comment


              • Originally posted by rederikus View Post
                I have only been online since 11/19/2016. I now use an RPi Jessie with an orange Prostick. I have several questions but my first is how do I set the LNA gain of the Prosick using FR24 software? Under PiAware, rtlsdr-gain is available. Is there a way to install rtlsdr-gain under FR24.

                Thanks
                If you want a quick and correct answer, ask this question in software thread, not in antenna thread.

                Gain of ProStick's LNA is NOT adjustable.
                In ProStick as well as in generic (black/blue) DVB-T dongles, it is the gain of Tuner chip RTL2832U which is adjusted.


                Gain of dongle is controlled and adjusted by dump1090. There are different ways to pass gain setting to dump1090, depending on which software you have installed.
                First you have tell exactly what software you have installed on your RPi:
                (1)Which image you wrote to your microSD card? Raspbian Jessie img, Piaware img or Flightradar24 img (Pi24 img)?
                (2) Did you install dump1090 separately or using the built-in dump1090 of FR24 feeder, or built-in dump1090 of Piaware img?
                (2) In which order you installed data feeders?
                Last edited by abcd567; 2017-02-05, 22:42.

                Comment


                • Originally posted by abcd567 View Post
                  If you want a quick and correct answer, ask this question in software thread, not in antenna thread.

                  Gain of ProStick's LNA is NOT adjustable.
                  In ProStick as well as in generic (black/blue) DVB-T dongles, it is the gain of Tuner chip RTL2832U which is adjusted.


                  Gain of dongle is controlled and adjusted by dump1090. There are different ways to pass gain setting to dump1090, depending on which software you have installed.
                  First you have tell exactly what software you have installed on your RPi:
                  (1)Which image you wrote to your microSD card? Raspbian Jessie img, Piaware img or Flightradar24 img (Pi24 img)?
                  (2) Did you install dump1090 separately or using the built-in dump1090 of FR24 feeder, or built-in dump1090 of Piaware img?
                  (2) In which order you installed data feeders?
                  Sorry I put this in the wrong place. I kinda thought that the LNA was part of the antenna. I guess that comes from years of working up radio masts...

                  To provide answers:
                  1.
                  a).I am running the latest released and updated version of Raspian Jessie running on an RPi3 and having rpi-update run within the last week.
                  b).I am using the standard FlightRadar24 installation. This is the version you get by typing bash -c "$(wget, etc. from root login. //not enough post to give the full command line. It thinks it's a link. Duh.

                  2. No, I did not. It came with the install.

                  3. I just followed the standard install procedure. Everything is stock software and installation -- so far.

                  I run two systems T-KCLT3 which is my main system and T-KCLT19 which is for playing with. Both use indoor attic mounted antennas. I cannot use external Antennas, HOA rules. T-KCLT uses an 8 element collinear antenna made from RG6 that I had lying around. This has a downfeed of about 25 feet and is also RG6 (sorry). I see a daily max range of 138 nm which is okay-ish, I guess. This system has the ProStick.

                  T-KCLT19 is the exact same software but a system that I can take out of service immediately. It uses a 16 element collinear antenna made from RG6 and does not work so well as the 8 element one. I'll have another go at this antenna later on. It uses a USB stick from jetvision.de. This is not a very good device and, tomorrow (Thursday) it will get an upgrade to a ProStick - Yay!

                  That's what I got, now, how may I change the LNA gain please. I realize this may not be possible with the software I currently have.

                  On the way to this I have installed dump1090-mutability and removed it (re-format microSD card), FlaightAware (hated their web pages and reporting.) and any number of other LInux mods. Now, I'm back to stock but have learned a tiny bit more.

                  I have other questions mainly related to antenna construction but for now, let's stick to LNA gain. I need this because I have a Hungarian LNA and 1090 Mhz filter en route as well as a 10dB SMA pad. I am also about to replace my downfeed with a 25 foot RG58U feed with SMA connectors (thanks ebay).

                  So I guess my question should be, how do I adjust the gain of the RTL2832U tuner chip? Is this possible with my installation?

                  That's me and where I am. Thanks for your help.
                  Last edited by rederikus; 2017-02-09, 02:13.
                  T-KCLT3 - Raspberry Pi3 Jessie, 8 element collinear indoor antenna

                  Comment


                  • Originally posted by rederikus View Post
                    .................................
                    ..................................
                    a).I am running the latest released and updated version of Raspian Jessie running on an RPi3 and having rpi-update run within the last week.
                    b).I am using the standard FlightRadar24 installation. This is the version you get by typing bash -c "$(wget, etc. from root login. //not enough post to give the full command line. It thinks it's a link. Duh.
                    ............................
                    ............................
                    So I guess my question should be, how do I adjust the gain of the RTL2832U tuner chip? Is this possible with my installation?
                    I have never used FR24 feeder with its built-in dump1090. Initially I used dump1090 (Malcom Robb), then for a long time I am using dump1090-mutability v1.15~dev. I was therefore not sure of the answer.

                    In order to reproduce your install, I formated my spare microSD card, installed Raspbian Jessie Lite (2017-01-11-raspbian-jessie-lite.img), then installed FR24 feeder by following command:
                    sudo bash -c "$(wget -O - http://repo.feed.flightradar24.com/install_fr24_rpi.sh)"

                    I then tried following commands, but did not succeed:
                    cd /usr/lib/fr24/
                    sudo ./dump1090 --gain 32.8

                    sudo fr24feed --gain 32.8

                    I then tried following method and it worked:


                    FR24Feeder-gain settings.png FR24Feeder-map.png

                    Code:
                    In your browser, go to page: http://<IP of Pi on LAN>:8754/settings.html
                    
                    In settings field "Process arguments", enter --gain <db> as shown below.
                    Process arguments: --net --net-http-port 8080 --gain 32.8
                    
                    Click "Save" button, then click "Restart" button.
                    
                    
                    
                    Now SSH to your RPi and give following commands:
                    
                    #First restart fr24feed for new gain setting to take effect.
                    pi@raspberrypi:~ $ sudo service fr24feed restart
                    
                    #Now check what is the Gain actually set.
                    pi@raspberrypi:~ $ service fr24feed status -l
                    ● fr24feed.service - LSB: Flightradar24 Decoder & Feeder
                       Loaded: loaded (/etc/init.d/fr24feed)
                       Active: active (running) since Sun 2017-02-12 00:20:00 UTC; 57s ago
                      Process: 2045 ExecStop=/etc/init.d/fr24feed stop (code=exited, status=0/SUCCESS)
                      Process: 2102 ExecStart=/etc/init.d/fr24feed start (code=exited, status=0/SUCCESS)
                       CGroup: /system.slice/fr24feed.service
                               ├─2115 /usr/bin/fr24feed -- --monitor-file=/dev/shm/fr24feed.txt --write-pid=/var/run/fr24feed.pid --quie...
                               └─2135 /usr/lib/fr24/dump1090 --net --net-http-port 8080 --gain 32.8 --raw --mlat
                    Last edited by abcd567; 2017-02-12, 12:32.

                    Comment


                    • Wow! Thank you abcd567. This is much appreciated. I cannot yet post code quotes or links but I did what you said and, naturally, it worked. I had been Googling for dump1090 command line parameters aand I found the "gain" argument myself. I had used it a couple of times and have so far seen little or no difference in minor gain adjustments. What I did not have and, you provided was a metric for seeing if the command had actually worked. Using "service fr24feed status" gave me the confirmation that gain changes were happening.

                      Thank you again. That was a lot of work on my behalf. I have played with custom installations my spare setup and have used dump1090-mutability by following your own guide. However I felt that when asking noob questions it would be better to have a standard baseline install from which to start.
                      T-KCLT3 - Raspberry Pi3 Jessie, 8 element collinear indoor antenna

                      Comment


                      • Okay, here is a question that is on topic for this thread. I am confused by the use of 75 Ohm RG6 cable and F-connectors when making collinear and other antennas and using RG6 as the downfeed to a 50 Ohm (SMA) input connector. I note that the balarad site uses a 75 to 50 Ohm transformer to convert from the antenna to the input. Most other designs I have seen do not do this. Can you explain, please.

                        I was practically weaned on 0.775 volts into 600 Ohms = 0dB. I have always taken great care to match the impedance of cables / connectors / inputs and outputs correctly. Power loss (via return loss) and extraneous noise have always been the penalty for not observing the rule.
                        T-KCLT3 - Raspberry Pi3 Jessie, 8 element collinear indoor antenna

                        Comment


                        • your right about impedance matching, but we are not transmitting. So the effects of the impedance miss match are there but they are basically very small, you would probably lose as much if not more through the insertion losses of a convertor.
                          T-EGLF8

                          Comment


                          • A good point. Thinking about this, it is pretty clear that dB losses due to a 75 to 50 Ohm mismatch are very small. Without doing the math, it will probably be less than 0.5dB. A not-so-good F-Connector termination will do more damage than that. I shall cease to worry about it.

                            You are right. I am more used to transmitter antennas than receivers.

                            I am working my was through all 264 pages of this thread. It is at turns inspiring, innovative, frustrating and fun. There's a lot of good information in here too.
                            T-KCLT3 - Raspberry Pi3 Jessie, 8 element collinear indoor antenna

                            Comment


                            • I have been testing several antennas with exact same setup so here is a polar distribution comparison.
                              The only difference is that colinear was fixed on different pole which is about 40cm higher and therefore I believe the range looks a bit better.
                              My current setup is in my signature...

                              antenna-comparison.gif
                              ======
                              T-EBCI32 (Raspberry PI 3 + RTL2832U/R820T2 USB dongle + Axing SVS 2-01 inline amp + TA1090EC filter)

                              Comment


                              • When 50 ohm is mixed with 75 ohm,
                                Reflection Coefficient Γ = (75-50)/(75+50) = 0.2
                                SWR = (1+Γ)/(1-Γ) = (1+0.2)/(1-0.2) = 1.2 / 0.8 = 1.5
                                Mismatch Loss in dB = -10 log (1 - Γ) = -10 log (1 - 0.2) = -10 log 0.96 = 0.177 dB
                                .

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