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Uputronics 1090Mhz ADS-B Filtered Preamp

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  • Uputronics 1090Mhz ADS-B Filtered Preamp

    Hi has anyone used Uputronics 1090Mhz ADS-B Filtered Preamp? looking for reviews ?

    Thanks
    Last edited by qc91; 2017-04-02, 23:45.

  • #2
    Hi.
    It seems expensive... 35=40€ur
    If you can, you try to buy two separate items :
    - one band-pass filter 1090MHz
    - one preamplier 50-2000MHz (7-12v).
    Price for these 2 items aren't more than 15€, so maybe 11 or 12€.

    See my assembly :
    radarvirtuel.flightradar24.lfpo64.002.jpg
    F4FFD - Dominique
    Station : T-LFPO64 / France
    Raspberry Pi3 + Dongle RTL/SDR + Preampli + Pass-band filter 1090MHz + Colinear Antenna 7dB + Battery 75A + Solar Panel 100W
    http://f4ffd.hamstation.eu

    Comment


    • #3
      @F4FFD,

      Why put the filter on the output?

      The purpose of a filter is to prevent other frequencies causing intermodulation noise in the band of interest, in active components such as amplifiers, and I can't see why the LNA preamp you've got there would be any exception.

      Sure, the filter has some insertion loss (more or less depending on the type of filter) and that will reduce SNR at 1090 MHz, but I would have thought that that the higher noise floor caused by intermod noise would be worse than the lower signal caused by the filter attached to the LNA input.

      Comment


      • #4
        Has anyone seen this DIY-gadget yet? Please do a google search for Barbouri
        Low Noise Amplifier for SDR Radio ADS-B
        , because I am not allowed to post URLs yet

        This device is combining LNA and filter on one PCB. It is featuring a CBP-1090C+ ceramic filter.

        I am thinking to build one for myself, though the filter costs quite a lot. Since I am residing in Germany, only shipping will be at about 20 Euros. Luckily I can get the PCB milled at the electronics laboratory at my workplace (and also the SMD soldering)

        One can also add the mentioned ceramic filter to the Uputronics 1090Mhz ADS-B Filtered Preamp, that will cost 48 currency units extra.

        Kind regards,
        Michael

        --if you want something done right do it yourself

        Comment


        • #5
          Originally posted by T-EDSB36 View Post
          One can also add the mentioned ceramic filter to the Uputronics 1090Mhz ADS-B Filtered Preamp, that will cost 48 currency units extra.

          --if you want something done right do it yourself
          Just as a general observation, RF, especially at microwave frequencies, is very much an art in its own right even when someone else has designed the PCB and you're just assembling a kit of components. If you don't know what you're doing, at best you might not get much benefit and, at worst, you might end up making things worse in terms of signal to noise ratio.

          Building colinear antennae is one thing, building a PCB is another. Even the material the PCB is made from matters: PCB track geometry is determined by proximity to ground plane and the dielectric constant of the PCB itself, so you can't necessarily just send PCB gerbers to a PCB fab company if you don't know what specifications to stipulate. Likewise, component selection is important: not all capacitors, for example, are created equal and in fact there are a variety of different types of capacitor and then different subtypes within each type each with their own particular characteristics which approach ideal in one axis or another only.

          Just to be clear: doing this yourself will probably work. But it might not work like it should. This kind of electronic engineering is all about margins, and trading one form of margin off another.

          So if you aren't an electronic engineer, or at least have a fairly decent working knowledge of electronics, my advice is not to skimp on the part of the rig where the signal is weakest and the margins are thinnest and buy a ready-made filter.

          Comment


          • #6
            Dear Strix technica,

            thank you for the quick response. I totally agree with your opinions towards HF engineering. All my knowledge is based on secondary school physics and the stuff I am learning for the amateur radio licence. Microwave is indeed a very tricky domain. In antenna construction, imprecisions in the dimension of millimeters mean a deviation of many megahertz. I have tested a self-made biquad with a network analyzer. I hit about 1070 MHz. A little too much wire. And every human presence in the closer range of the antenna produced significant detuning.

            Maybe buying a ready-made LNA/Filter-Combination isn't so bad after all, at least I could afford it (with ceramic filter, of course ).

            Comment


            • #7
              Originally posted by T-EDSB36 View Post
              I have tested a self-made biquad with a network analyzer. I hit about 1070 MHz.
              If you are fortunate enough to have access to a VNA then you are very lucky indeed and can test the performance of whatever it is that you build. However, a VNA doesn't tell you how to fix any problems you might find, it can only tell you what is. Of course, if you even know what a VNA is and how to use one, you probably know what to do anyway

              Either way, knowing what to do depends on a decent understanding of RF engineering and especially transmission line design. Worse, there is very little you can do about bad geometry on a PCB except have another one made, at which point any cost savings made by DIY would be lost and you may as well buy a commercially manufactured and tuned ceramic or cavity filter. Plus you get warranty and support should there be a problem.

              It's easy to obsess over the RF engineering involved more than is warranted. How important are impedance mismatches such as those caused by incorrect transmission line geometry? Well, impedance control is pretty crap with RTL-SDR solutions anyway because the receiver is designed for 75Ω antennae but SDRs, notably the FightAware ones which perform the best for this application, use 50Ω SMA. Then there's the impedance of your antenna and feeder which might be anywhere between 36Ω and 75Ω (or more, if you're unlucky) depending on which cable used and what type of antenna. If memory serves, 50-75Ω mismatch loss is somewhere in the order of -1 dB, so not worth worrying about. Also, every connector adds both insertion loss and impedance discontinuities, so each connector, adapter and impedance discontinuity adds up where SNR can already be pretty low.

              See what I mean about obsessing over perfect engineering?

              Fact is, there is no substitute for more S and less N. Height to clear nearby obstructions will give you far better results than tinkering with LNAs and filters. The only exception to that is if you have a strong RF source on another band, eg a GSM base station in which case a decent, high-Q bandpass filter is indispensible. After that, a decent gain antenna will give you the best return on investment.

              People forget that antennae are passive devices: 'gain' is commonly understood to mean amplification, but that's just not the case with antennae. Antenna gain is pattern, where the antenna is most sensitive. For this application, high gain antennae typically mean long and flat patterns, and this is a good thing even though there are a/c nearby at a relatively high angle. That just doesn't matter: an a/c directly overhead at FL400 is only 6.6 nm away, where we're typically concerned with a/c 150-300 nm away. A bit of basic trigonometry, not allowing for the curvature of the earth, will tell you that an a/c 100 nm away makes about a 3 angle with the normal (ie perpendicular to the axis of the antenna), so virtually everything of interest is on the horizon. Lateral gain, therefore, is where it's at for ADS-B radars. Most high angle a/c are close and powerful enough (relative to distant, low-angle a/c) that the weaker gain at that angle doesn't matter.

              After that, the type of coax you use makes a huge difference. Good quality RG6 (75Ω) has a loss of about -2 dB per 10 metres, where the best RG58 (50Ω which, unfortunately, is what most RF devices are designed for) has a loss somewhere around the -7–9 dB mark. So unless there is a masthead LNA with a bias T to feed it power and a weatherproofed masthead filter to limit intermod noise in the LNA, it's probably better to use mismatched cable and eat the reflection loss than use the right impedance coax and eat the dielectric loss on a long run of cable.

              See this article for an explanation of why rx-only gear (such as TV) is 75Ω where everything else is 50Ω.

              Filters, LNAs and such are last resorts when you've done everything to improve SNR that you can (with the exception of powerful nearby radio sources that cause intermodulation noise in any amplifier).

              (I expect you know all this, but it bears repeating for the benefit of other readers.)

              Originally posted by T-EDSB36 View Post
              And every human presence in the closer range of the antenna produced significant detuning.
              Which will happen regardless, including with commercially-bought equipment, because all antenna designs must make assumptions about what's in the near field. Resonance depends on so many factors anyway, so the best you can do is make your best attempt and live with the results.

              Originally posted by T-EDSB36 View Post
              Maybe buying a ready-made LNA/Filter-Combination isn't so bad after all, at least I could afford it (with ceramic filter, of course ).
              That's what I would do
              Last edited by Strix technica; 2017-06-14, 01:37.

              Comment


              • #8
                Originally posted by Strix technica View Post
                @F4FFD,

                Why put the filter on the output?

                The purpose of a filter is to prevent other frequencies causing intermodulation noise in the band of interest, in active components such as amplifiers, and I can't see why the LNA preamp you've got there would be any exception.
                Hi,
                I think like you, and I've try to insert this 1090MHz filter between the preampli and the antenna but infortunatly the best result in RX is to put this filter between preampli and SDR gongle. I don't know why but it works
                F4FFD - Dominique
                Station : T-LFPO64 / France
                Raspberry Pi3 + Dongle RTL/SDR + Preampli + Pass-band filter 1090MHz + Colinear Antenna 7dB + Battery 75A + Solar Panel 100W
                http://f4ffd.hamstation.eu

                Comment


                • #9
                  Originally posted by F4FFD View Post
                  Hi,
                  I think like you, and I've try to insert this 1090MHz filter between the preampli and the antenna but infortunatly the best result in RX is to put this filter between preampli and SDR gongle. I don't know why but it works
                  If you don't have an environment in which intermodulation noise is a significant problem, then it won't make any difference where you place the filter. You may or may not even benefit much from one in the first place, it all depends on ambient conditions.

                  But if you have a strong RF source nearby, it seems to me that the filter must present before the LNA. The filter will attenuate the signal of interest, but that is compensated for by the LNA and it will attenuate the intermod noise even more therefore SNR will be better than if the filter presents after the LNA.

                  Comment

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