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NooElec with small antenna ---> FA Pro Stick + FA 1090 Antenna = worse results?

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  • NooElec with small antenna ---> FA Pro Stick + FA 1090 Antenna = worse results?

    I had a cheapo nooelec DVBT stick with the antenna it comes with... little mag mount 6" antenna. Put it outside on my patio, stuck the antenna to the top of my bbq grill, and set up fr24feed. Didn't modify any settings.

    I was seeing 1200-1300 aircraft/day with some of them 70nm away.

    Interested in kicking it up a notch, I upgraded - I bought a "Flightaware Pro Stick USB ADS-B receiver dongle which includes an internal 1090 MHZ band pass filter" AND the FlightAware-branded 26" long 1090mhz antenna. Attached it to my patio up higher than the previous antenna's location. Connected to the Pro Stick with a short 16 inch cable.

    Booted up the pi and was disappointed to see I was only getting aircraft 40nm away and only ~700/day. I switched over to dump1090-mutability and ran the python script to figure out my ideal gain... ended up being 42.1dB (with 29dB being a close second)... I'm now seeing ~900 aircraft/day and a max distance of 54nm.... still not even close to the cheap stick, let alone better!

    Any ideas? Here's my monitor.txt:

    Code:
    ac_map_size="3072"
    build_arch="static_arm"
    build_flavour="generic"
    build_os="Linux"
    build_revision="T201704200925"
    build_timetamp="Apr 20 2017 09:25:30"
    build_version="1.0.18-9"
    cfg_baudrate=""
    cfg_bs="no"
    cfg_host="127.0.0.1:30005"
    cfg_mpx=""
    cfg_path=""
    cfg_raw="no"
    cfg_receiver="beast-tcp"
    cfg_windowmode="0"
    d11_map_size="18"
    feed_alias="T-KSJC45"
    feed_configured_mode="UDP"
    feed_current_mode="UDP"
    feed_current_server="83.140.21.87"
    feed_last_ac_sent_num="0"
    feed_last_ac_sent_time="1499971100"
    feed_last_attempt_time="1499797260"
    feed_last_config_attempt="1499797259"
    feed_last_config_info=""
    feed_last_config_result="success"
    feed_last_connected_time="1499797260"
    feed_num_ac_tracked="8"
    feed_status="connected"
    feed_status_message=""
    fr24key="XXXXXX"
    gps_tods="0"
    last_json_utc="1499971026"
    last_rx_connect_status="OK"
    last_rx_connect_time="1499948865"
    last_rx_connect_time_s="2017-07-13 12:27:45"
    last_rx_global_timeout="1499948860"
    local_tods="67075"
    mlat-mode="UDP"
    mlat-number-seen="7"
    mlat-ok="YES"
    mlat-started="YES"
    mlat-time-last-ping="1499971090"
    mlat-time-last-push="1499971030"
    mlat-time-last-push_count="1"
    mlat-time-last-seen="1499971105"
    mlat-time-stats="1499971105"
    mlat-uplink-stats="0"
    mlat_problem="no-config"
    msg_ring_full="0"
    msg_ring_length="0"
    num_global_timeouts="12"
    num_messages="841760"
    num_resyncs="0"
    offline-mode="no"
    rx_connected="1"
    shutdown="no"
    time_update_utc="1499971085"
    time_update_utc_s="2017-07-13 18:38:05"
    timing_is_valid="1"
    timing_last_drift="-0.0003"
    timing_last_offset="+0.0009"
    timing_last_result="success"
    timing_source="NTP"
    timing_time_last_attempt="1499971081"
    timing_time_last_success="1499971081"
    timing_time_since_last_success="626"

    For what it's worth, here are the dump1090 params I'm using:

    Code:
    /usr/bin/dump1090-mutability --net --gain 42.1 --ppm 0 --fix --lat xxx --lon -xxxx --max-range 300 --net-ri-port 30001 --net-ro-port 30002 --net-bi-port 30004,30104 --net-bo-port 30005 --net-sbs-port 30003 --net-heartbeat 60 --net-ro-size 500 --net-ro-interval 1 --net-buffer 2 --net-bind-address 127.0.0.1 --stats-every 3600 --write-json /run/dump1090-mutability --write-json-every 1 --json-location-accuracy 2 --quiet


    I am located in San Jose, CA about 4 miles from SJC.

  • #2
    Originally posted by klinquist View Post
    I switched over to dump1090-mutability and ran the python script to figure out my ideal gain... ended up being 42.1dB (with 29dB being a close second)... I'm now seeing ~900 aircraft/day and a max distance of 54nm.... still not even close to the cheap stick, let alone better!
    Usually, problems with FA ProSticks are related to too much gain but evidently, you've already seen to that. That said, 42 dB seems pretty high given there's (at least) a 20 dB LNA in there already, so your SNR's probably pretty rubbish.

    I wonder if your problem mightn't be intermodulation noise. I haven't been able to find any satisfactory indications as to whether the Pro+'s BP filter is before or after the LNA, but I suspect it's probably after. That being the case, if there's a strong RF signal on any frequency, it's probably going to clobber the weak ADS-B signal.

    Also, the Pro+'s BP filter isn't narrow enough to exclude GSM900 (worse, GSM950) signals, so if you have any cell base stations nearby then intermod is a likely candidate. I'm pretty sure I've got that problem because there's a cluster of base stations about 100 yards from me.

    There isn't really anything you can do about it except install a decent, 3rd party cavity (example) or SAW bandpass filter between your antenna and Pro+.
    Last edited by Strix technica; 2017-07-14, 18:07.

    Comment


    • #3
      What power supply are you using with your RPi? Rating in amps and volts? And is the Pro Stick connected directly to the RPi or are you using a USB cable and if so, what length?

      And is it the orange or blue Pro Stick?
      Mike


      www.radarspotting.com

      Radarspotting since 2005

      Comment


      • #4
        Originally posted by Anmer View Post
        What power supply are you using with your RPi? Rating in amps and volts? And is the Pro Stick connected directly to the RPi or are you using a USB cable and if so, what length?
        PSU problems won't account for reduced a/c count or range. If there were a PSU problem, something would have crashed or the USB link would have been broken.

        Originally posted by Anmer View Post
        And is it the orange or blue Pro Stick?
        OP said it was the blue Pro+.

        Comment


        • #5
          The Pro Stick Plus has an integral SAW filter, which is located between front-end rf amplifier chip and the tuner chip.

          In areas with lot of Cell phone signal, these un-filtered cell phone signals oveload the pre amplifier, as well as cause cross-modulation while passing through the pre amplifier chip.

          The solution to this problem is simple: add a filter between antenna and Pro Stick Plus. Flight aware filter is now available at Amazon.com at US $15.50

          https://www.amazon.com/gp/aw/d/B010GBQXK8

          Pro Stick Plus - With & Without Filter at my location
          My location has lot of Cell Phone & other interfering signals.

          Last edited by abcd567; 2017-07-14, 21:39.

          Comment


          • #6
            Originally posted by abcd567 View Post
            The Pro Stick Plus has an integral SAW filter, which is located between front-end rf amplifier chip and the tuner chip.
            I suspected as much (re placement).

            Originally posted by abcd567 View Post
            The solution to this problem is simple: add a filter between antenna and Pro Stick Plus. Flight aware filter is now available at Amazon.com at US $15.50

            https://www.amazon.com/gp/aw/d/B010GBQXK8
            Though it's "made" (likely re-wrapped) by the same company, that's no guarantee that the linked BP filter is equivalent to the BP filter in the Pro+ stick. That said, it's worth checking whether anybody has measured the actual knee-point and dB-per-decade properties of this before buying it if you suspect intermod noise.

            Even taken at face value, 980 MHz is uncomfortably close to the upper edge of the GSM900 band, so it probably isn't adequate for GSM950. I don't know what the actual bandwidth of ADS-B is, but it can't be much more than 1–2 MHz so something with 70 MHz bandwidth is absurdly broad for this application.
            Last edited by Strix technica; 2017-07-14, 22:43.

            Comment


            • #7
              Originally posted by Strix technica View Post
              I suspected as much (re placement).
              Two options:
              (1) Adding 2nd SAW filter between antenna input and rf pre-amplifier (extra cost)

              (2) Relocating existing SAW filter from current location (between rf pre-amp and tuner), to new location (antenna input connector and rf pre-amp).

              I have made these suggestions in Flight aware forums recently.

              http://discussions.flightaware.com/p...5.html#p207845


              http://discussions.flightaware.com/p...8.html#p208318

              .

              Comment


              • #8
                Or just buy a separate cavity or SAW filter, which you get to choose, that has narrower bandwidth and higher order to knock out adjacent GSM signals.

                And I'd say that FA's BP filter is a poor choice, even if it is a SAW filter. If you look at this frequency response plot (bottom of page), you'll see that it has a bandwidth of about 300 MHz beginning somewhere in the range of 930–950 MHz. That's going to pass a lot of GSM, so it's pretty useless.

                See also this analysis (scroll to bottom) and this test.

                In general, discrete filters cost a lot more, but you get what you pay for.

                Comment


                • #9
                  Originally posted by Strix technica View Post
                  OP said it was the blue Pro+.
                  Strange, all I can see is:

                  I bought a "Flightaware Pro Stick USB ADS-B receiver
                  Mike


                  www.radarspotting.com

                  Radarspotting since 2005

                  Comment


                  • #10
                    Originally posted by Anmer View Post
                    Strange, all I can see is:
                    Arg. I read what I expected to read, given the following:

                    Flightaware Pro Stick USB ADS-B receiver dongle which includes an internal 1090 MHZ band pass filter
                    If it has the bandpass filter, then it's the blue Pro+.

                    Comment


                    • #11
                      The Flightaware stand alone filter is an LC filter.
                      The Pro Stick + (Blue) has an integral SAW filter.

                      A Cavity filter will sure give precise and narrow band width, but cost $100 to $150(6 to 10 times the cost of LC or SAW filter).

                      In my case, Flightaware's $15.50 LC filter did the job well.
                      In few very severe noisy location, a costly cavity filter may needed. On ebay 1090 Mhz SAW filter are available for around $20, and may be good, but I did not try these.

                      Comment


                      • #12
                        Have you tried the Pro Stick with your previous antenna and vice versa? The existing DVB-T "dongle" with the FlightAware antenna?

                        You don't mention what coax cable you're using?
                        Mike


                        www.radarspotting.com

                        Radarspotting since 2005

                        Comment


                        • #13
                          LC FILTER SCHAMETICS

                          UNBALANCED LC LADDER



                          BALANCED LC LADDER



                          FLIGHTAWARE FILTER INSIDE




                          HUNGARIAN FILTER WITH TAI-SAW CHIP
                          US $19.99 http://www.ebay.com/itm/112472645896




                          CHINESE FILTER
                          US $28.95 http://www.ebay.com/itm/331993013752
                          Passband : 1086 ~ 1094 MHz (Not mentioned what type of filter is inside. Seems to be a TAI-SAW Chip, but not sure.)







                          TAI-SAW FILTER CHIP





                          Comment


                          • #14
                            Flightaware antenna is a high gain antenna (6 dBi), while mag mount whip antenna supplied with DVB-T is a low gain (1.5 ~ 2 dBi)

                            The Flightaware antenna therefore picks much more Cell Phone signals, and overloads the rf preamp chip if a filter between antenna and ProStick is not used.

                            TEST-1: Comparison of Cantenna (Gain ~2 dBi) vs Flightaware Antenna (Gain 6 dBi) WITHOUT FILTER and with Generic DVB-T

                            .







                            TEST-2: Comparison of a Spider Antenna (Gain ~2 dBi), and Flightaware antenna (Gain 6 dBi) With ProStick/ProStick Plus


                            Comment


                            • #15
                              TEST-3: Flightaware Antenna and Pro Stick/ProStick Plus with Attenuators
                              Gain Setting throghout the experiment = 38.6 dB










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