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  • FlightAware 1090Mhz Bandpass Filter

    Last week my FlightAware bandpass filter arrived Well after having to go to the Sorting office as customs duty had to be paid.

    I made a big mistake, I bought on Ebay and it was shipped from the US, $24.99 + $12.00 Postage = 26.52 GBP, then add nearly 4.00 customs duty and 8.00 handling charge by the Royal Mall, totalling 38 pounds.

    The big mistake was I found out after ordering it Icould have bought it from Amazon in the UK for 15.54 and got it a lot quicker.

    Reason for purchase is I have two mobile phone masts nearby and suspected some overload of the dongles front end.

    So I put it in circuit between the Antenna feed and the short SMA-M to MCX lead, OK that was Monday last week, almost immediately found a sharp drop in performance, it was left in circuit for two full days (removed last Thursday).

    Taking the averages for Tue/Wed & Fri/Sat/Sun/Mon/Tue with no other changes to the system these are the figures:
    Date Aircraft positions Distance nm UpTime%
    Sun 8 May 16 1463 86416 158 100
    Mon 9 May 16 1269 73979 140 100 fitted filter 10am
    Tue 10 May 16 1040 67947 109 100
    Wed 11 May 16 1023 61873 111 100

    Thu 12 May 16 1446 93183 147 100 removed filter 11am
    Fri 13 May 16 1532 114127 347 100
    Sat 14 May 16 1337 97393 155 100
    Sun 15 May 16 1496 116442 165 100
    Mon 16 May 16 1580 120134 159 100
    Tue 17 May 16 1579 106502 153 100


    10-11 May 1031.5 64910 110 100
    13-17 May 1504.8 110919.6 195.8 100
    Filter/
    Performance 68.55% 58.52% 56.18%


    OK so I do not have a issue Mobile phone transmissions and the figures are in line with the quoted insertion loss of <2.5Db

    All not lost as I intend to add an aerial Amp next 0-2000Mhz with up to 30Db gain, I may need some attenuation...
    Last edited by G8VXY; 2016-05-18, 08:53.
    """Learning is a treasure which accompanies us everywhere"""

  • #2
    Hi,

    Having had very varying results with the FA filter in different RF environments I started to wonder what was going on.
    In some RF-dense areas it more or less doubled the range, but in others where we had GSM towers close it hardly helped at all.

    After checking it's actual specs on a VNA, it makes more sense, see below.

    1. At least the one we tested had an insertion loss of around 3 dB. That is worse than their claimed spec and quite a lot for this application. Maybe a production variation/ QA problem

    2. The filter is almost wide-open down to 925 MHz. At 960 MHz the attenuation was only 3.5 dB ! That means that this filter is not sharp enough to provide protection from GSM900 Downlink !!

    3. At 862 MHz it attenuated almost 60 dB, so it provides great protection from GSM850 as used in USA, and all DVBT transmitters in the UHF range.

    4. Of course, if you don't have any RF interference, the filter is just a 3dB attenuator, and we see that clearly testing on rural sites.


    It's a very cheap filter, it is as always a compromise but can still help a lot UNLESS your problem is GSM900 cell towers.

    A very good filter was tested as well, a commercial 1100 MHz 7-cavity Chebyshev BPF. It had 0.8 dB insertion loss, and -80 dB attenuation at 960 MHz, as well as on 1230 MHz. But when sold new, this filter was surely more than 10 times the price of the FA filter....

    Photos of VNA measurements: https://www.dropbox.com/sc/vpwjancn9...jWnAQK9RkQ16Ga

    FA-filter -3dB @1090 MHz:
    https://www.dropbox.com/s/j9ljc8zn5p...0FA1.jpeg?dl=0

    FA-filter -3.4dB @960 MHz:
    https://www.dropbox.com/s/mtreqswx2v...0FA2.jpeg?dl=0

    FA-filter -59dB @862 MHz:
    https://www.dropbox.com/s/5gaxyb33j2...0FA3.jpeg?dl=0

    7-cavity BPF, -81dB @965 MHz:
    https://www.dropbox.com/s/z8cr476pg5...RCT3.jpeg?dl=0


    BR

    /M
    Last edited by MrMac; 2016-05-19, 23:07.
    F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESNV3 F-ESSL4, F-LFMN3
    P-ESGR, P-ESIA, P-ESIB, P-ESGF
    mrmac (a) fastest.cc

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    • #3
      I have a 1/4 wavelength groundplane antenna (Cantenna), DVB-T dongle black $9, 12 ft / 4 m RG6 coax between antenna and dvb-t, which is plugged into Ras Pi model 2.

      I tried by replacing one item at a time
      1) Generic DVB-T (black) replaced by FlightAware's ProStick (dvb-t with built-in rf amplifier).
      2) Cantenna replaced by FlightAware 1090 Mhz antenna

      I did not find any improvement.

      However when I replaced Black DVB-T + Cantenna by ProStick + Flightaware Filter + FlightAware 1090 mhz antenna my figures of message and plane count both increased by 30%

      Seems ProStick + FA Filter + FA antenna make a "matched set"
      Last edited by abcd567; 2016-06-15, 23:27.

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      • #4
        got it[emoji1]


        Sent from my iPhone using Tapatalk

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        • #5
          I am not still fully convinced that a higher power front end receiver has much advantage if it requires a lossy antenna filter.
          My personal opinion is that any receiver that is marketed with an "extra antenna filter" that is passive and lossy is unusual to say the least and is not very credible.

          Comment


          • #6
            Originally posted by Sam26K View Post
            I am not still fully convinced that a higher power front end receiver has much advantage if it requires a lossy antenna filter.
            My personal opinion is that any receiver that is marketed with an "extra antenna filter" that is passive and lossy is unusual to say the least and is not very credible.
            The FA Antenna+FA Filter+ProStic is the best option I have used up to now.

            I have 2 setups. My stats show the FA combo gives much better performance: Message rate 182%, Plane count 114%

            System-1: Cantenna + 12 ft RG6 Coax + 12 inch RG316 pigtail + Black DVB-T (No Amplifier) >> plugged directly into Orange Pi PC
            System-2: FA Antenna + 4 ft RG6 Coax + 4 inch RG316 pigtail + FA Filter + ProStick >> plugged directly into RPi Model2

            Note:
            (1) Both antennas are at same location in same vertical line. Horizontal distance = 0, Vertical distance = 1 m / 3 ft
            (2) There is NO AMPLIFIER with Cantenna + Generic DVB-T, while ProStick has a built-in RF amplifier.




            Comment


            • #7
              Have to agree that the FA Dongle with the Filter is the best setup so far but comparing the difference can be difficult when I can only run one at a time and atmospheric and even participation do seem to muddy the water in comparison tests.
              """Learning is a treasure which accompanies us everywhere"""

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