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  • @abcd567

    Maybe I didn't convey in that post that I'm on top of the basics.

    The point of the post was to relate how dramatic the effect of signal overload can be. It wasn't just a reduction in displayed aircraft or range, it was a drop from seeing numerous aircraft, some beyond 175nm to seeing virtually nothing. Virtually nothing was just one aircraft within about 15nm. It was way more dramatic an effect than I would have imagined.

    Some additional learning points from this scenario were:

    + Don't assume an antenna is going to work well solely based on reflected power reading i.e. VSWR, however its a good sign that it will work to some degree
    + Range should not be used as the sole indication of antenna effectiveness, look at message rate and the number of 'hits' over a significant period of time
    + Finally, don't ever take something at face value, check it out

    My 'fall back' and the 3 element co-linear I mentioned previously are shown below (original graphics as downloaded, not my actual versions).

    150_x_150 colinear.jpg

    5-8th.jpg

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    • Went and bit the bullet and ordered an FA antenna and set it up last weekend replacing the old 8-element CoCo;

      Antenna.png

      It's now running 'naked' (ie no amp which was in that piece of pipe you can see on the fence) into a FA Prostick+. I'm now getting regular hits 200Nm+ and yesterday set a new bench-mark of 224Nm to the NE out over the Coral Sea.

      The mast consists of a 1.8m J-bracket (designed for mounting TV antennas) sitting 1.7m above the ground to which I've added an old pool cleaner pole which adds another 3.8m on with the antenna clearing the house roof-line.

      During the week I ran the 'do I need a filter' test and there's large spikes from the not-too-far distance GSM tower (about 1km away slightly to the right of that tree)
      1090Mhz waterfall and spectrum.jpg
      so I've ordered a filter from Hungary via eBay and it should be here in a week or so.
      https://www.ebay.com.au/itm/ADSB-Fil...53.m1438.l2649
      I'll test it locating it up top of the antenna and also just before the Prostick to see if there's any discernible difference.
      Last edited by petercr; 2018-05-19, 10:46.

      Comment


      • Originally posted by petercr View Post
        Went and bit the bullet and ordered an FA antenna and set it up last weekend replacing the old 8-element CoCo;

        [ATTACH=CONFIG]9463[/ATTACH]

        It's now running 'naked' (ie no amp which was in that piece of pipe you can see on the fence) into a FA Prostick+. I'm now getting regular hits 200Nm+ and yesterday set a new bench-mark of 224Nm to the NE out over the Coral Sea.

        The mast consists of a 1.8m J-bracket (designed for mounting TV antennas) sitting 1.7m above the ground to which I've added an old pool cleaner pole which adds another 3.8m on with the antenna clearing the house roof-line.

        During the week I ran the 'do I need a filter' test and there's spikes from the not-too-far distance GSM tower
        [ATTACH=CONFIG]9465[/ATTACH]
        so I've ordered a filter from Hungary via eBay and it should be here in a week or so. I'll test it locating it up top of the antenna and also just before the Prostick to see if there's any discernible difference.
        Good to hear its worked well for you. It still leaves some room to experiment, so win-win!

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        • About DC blocker: Or you could open up the amp, the lid is often just a very thin metal plate with press fit, and remove the power pass coil that are easily spotted as it goes from input to output and are usually the only component that are placed on the circuit board on the lid side.

          Remember that those sat amplifiers could have a noise figure of 5dB and the generic 50-3000MHz $25 amplifiers from Ebay have 0.8dB or even less. You can dig up more signals 4dB down in the noise with those low noise amplifiers. It's like you had doubled the gain of your antenna.
          Last edited by Ubbe; 2018-05-19, 20:23.

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          • Originally posted by petercr View Post
            During the week I ran the 'do I need a filter' test .....
            In October & November 2017, I created two identical threads describing method for RF Scan as listed below:

            28 October 2017 - FlightRadar24 forum, Titled: Find Out Existing RF Signals (Cell/Mobile/Pager etc) In Your Area

            09 November 2017 - FlightAware forum, Titled : Do I Need A Filter?

            Immediately after creation of FR24 thread, I realized that its title is too long, and wanted to modify it to the shorter name "Do I Need A Filter?", but the FR24 forum does not allow to change thread title once it is created.

            Few days later when I created the same thread in FlightAware forum, I used the short and handy name "Do I Need A Filter?"
            Last edited by abcd567; 2018-05-19, 22:33.

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            • Originally posted by abcd567 View Post
              Immediately after creation of FR24 thread, I realized that its title is too long, and wanted to modify it to the shorter name "Do I Need A Filter?", but the FR24 forum does not allow to change thread title once it is created.
              ... https://forum.flightradar24.com/thre...ignals-In-Area
              Posts not to be taken as official support representation - Just a helpful uploader who tinkers

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              • @Oblivian
                Thank you so much for using your Super Moderator authority to change/shorten the thread title.
                The title now sounds much better.

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                • I am using two spiders, one which just uses the coax with the legs pushed into the shield and the other is using a S0-239,PI-259 setup. Both are as effective as the other. The cantenna was great as well but a little less range the the spiders.

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                  • Ok, I looked at the design of several Coaxial co-linears and decided I'd have a go at building my own. Based on my knowledge of Satellite systems and knowing the larger the area of the dish the more sensitive it is to weaker signals, I thought I'd try something with a little more surface area. Secondly because of the 'skin effect' at 1090 Mhz, I'm not convinced coax is an ideal medium for the Job.
                    After some calculations I arrived at using 18 guage Tinned copper wire for an inner and 15mm copper water pipe as the outer. Whilst pottering around in the garden I hit upon the idea of using bamboo cane as the dielectric, after all it's a very dry, and has a rather convenient hollowness about it. - Here are pictures of the prototype, which is working rather well and outperforming a Jetvision antenna mounted some 7 feet higher up!CIMG3757.jpgCIMG3758.jpgCIMG3759.jpgCIMG3760.jpg Characteristic Impedance 45.7ohms - feeder 50ohms, next step to build the filter and dongle inside with the antenna, I have tested a 10metre proprietary USB2 extension lead (with built in buffer) and it works fine with a respberry PI - looking at using 1" copper pipe and a more efficient spacer for the Mkii!.
                    Last edited by mem0tap; 2018-07-16, 22:52. Reason: further data appended,

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                    • Makes an interesting alternative to electrical conduit that I had my previous CoCo installed in...

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                      • Originally posted by petercr View Post
                        Makes an interesting alternative to electrical conduit that I had my previous CoCo installed in...
                        So pleased with it, I've designed a prototype using 8.5mm water pipe as a core and 22mm as a shield, 51.3 ohm 66pf/metre 175 nH/Metre, I'll be using 100% air dielectric so propagation will be a shade under 100% with 137mm sections - working on the jigs to build it (as you can see below BUT the soldering Iron is not up to it) and there are other problems I foresee, - no more pipe for one thing!!! and i can only buy it 3m lengths The original prototype seems to be happy to receive echoes from 160nm against the original Jetvision 109nm based only on 24 hours of data. CIMG3761.jpg IF anyone is interested I'll keep posting pictures and progress otherwise I'll save myself some time.
                        Last edited by mem0tap; 2018-07-17, 17:54.

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                        • A couple of questions being no expert in this subjects.
                          -Can be two different type antennas be plugged at the same time (A spider and a Coco for example)?
                          -Using a Coaxial antenna can bring much improvement compare to a spider antenna? If so, what type of improvement? An increase in the distance of the planes registered or an increase in the hits/position catched within the same distance?

                          Comment


                          • Originally posted by goku1976 View Post
                            A couple of questions being no expert in this subjects.
                            -Can be two different type antennas be plugged at the same time (A spider and a Coco for example)?
                            -Using a Coaxial antenna can bring much improvement compare to a spider antenna? If so, what type of improvement? An increase in the distance of the planes registered or an increase in the hits/position catched within the same distance?
                            There are multiple antenna installations (Yagis e.g) - but different types of antenna? - if you did manage to couple them so that all impedances lived well with each other, you would find 'phasing errors' which means the signal would mostly arrive at each antenna at different times sometimes adding sometimes cancelling. I would suggest you either use an antenna switching unit (but there will be losses this way) or have separate receivers. - Despite designing my own antennas I'm not an antenna expert, nobody is, it's a black art, guided by experience and a few rule of thumb calculations. I reckon for every successful antenna there's a few dozen in the bin!

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                            • Originally posted by goku1976 View Post
                              A couple of questions being no expert in this subjects.
                              -Can be two different type antennas be plugged at the same time (A spider and a Coco for example)?
                              -Using a Coaxial antenna can bring much improvement compare to a spider antenna? If so, what type of improvement? An increase in the distance of the planes registered or an increase in the hits/position catched within the same distance?
                              You cannot connect two at the same time (technically you can, but theres no advantage +its VERY difficult to do correctly)

                              The spider is a simple "half wave dipole" and as simple as antennae get - the coco (colinear) adds more elements , and so more "gain" ie you can receive further away signals.

                              The crux of the matter is accuracy... and we are talking fractions of a millimetre at these frequencies - the spider is only critical at the centre element, so you have a good chance of getting "near" - and near enough is usually good enough !!!!

                              When making multi element antennae, the errors in cutting mount up... and its easy to create an antenna that is far worse than a simple dipole.

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                              • Rooster:
                                thumb-single.jpg thumb-single.jpg thumb-single.jpg
                                Fully agree with you.

                                Glad to see you after a long gap. Welcome back.

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