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Thread: New 1090MHz Bandpass filter from Flightaware (abcd567 is a star! :)

  1. #1
    Flight attendant
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    New 1090MHz Bandpass filter from Flightaware (abcd567 is a star! :)

    I just noticed FlightAware have released a new 1090MHz Bandpass filter with a smaller passband (here), so I wondered if I need one as I already have one of the original filters.

    A bit of searching and of course abcd567 has already highlighted the exact steps needed to work it out...

    These are a couple of sections from my result (with the original filter in place), so given how much brighter 925-960MHz is than 1090MHz it looks like I'd benefit from the smaller frequency range of the new filter.

    original-filter.png

    Thanks, abcd567.

  2. #2
    Captain abcd567's Avatar
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    Quote Originally Posted by elljay View Post
    (abcd567 is a star! : )
    Thanks, abcd567.
    Thanks for the compliments. You’re welcome bro. It’s my pleasure.


    This new filter is particularly useful for countries where mobile/cell phones use GSM900.
    The original FA Filter could not eliminate signals in this band, but the new version has a narrower pass-band, and can eliminate signals in this band also.


    GSM-900:
    This band of frequencies is used for mobile/cell phones in most parts of the world (ITU-Regions 1 and 3): Africa, Europe, Middle East, Asia (apart from Japan and South Korea where GSM has never been introduced) and Oceania.

    GSM-850 (also known as GSM-800):
    This band of frequencies is used for mobile/cell phones in most of North, South and Central America (ITU-Region 2)

    Here is scan in North America (Toronto, Canada) which I did yesterday, showing very little signal (pager??) in 900 Mhz band (GSM900) and a lot in 800 Mhz band (GSM800/GSM850)

    Scan ProStic-No Filter-800-850Mhz.png

    Scan ProStic-No Filter-850-900Mhz.png

    Scan ProStic-No Filter-900-950Mhz.png

    Above scan done by method given here:
    Do I need a Filter? - Find RF Signals In Area

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    Last edited by abcd567; 2019-02-04 at 17:27.

  3. #3
    Flight attendant
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    Well, the new filter arrived yesterday. It has definitely made a difference to the signal!

    filters.png

    ...but I can't spot any change to the data reported by Dump1090 so far...

  4. #4
    Purser
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    It's hard to estimate from these frequency scans if the noise will actually interfere with reception.

    What antenna/dongle/gain are you using?
    Last edited by wiedehopf; 2019-02-08 at 13:13.

  5. #5
    Flight attendant
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    I've got a Jetvision SCO-1090-MCX antenna mounted on the roof with a Flightaware Orange dongle. The gain changes based on a script that runs a couple of times a day (midnight and 8am) - see the graph in the bottom middle here. The gain "goodness" is the average of the percentage of each gain of the highest gain of that test of each of the measures equally weighed: # aircraft, # positions, #usable messages, max distance and average distance as reported by dump1090. e.g. this morning's 8am run:

    Code:
    ===Overall Totals From Log File===
    Gain A/c Posn UsbMsg MaxD  AvgD
    37.2 259 2264  39093 147.0 52.4
    38.6 260 2169  39054 146.3 54.4
    40.2 258 2175  39192 138.8 52.4
    42.1 265 2211  39653 140.0 50.1
    43.4 268 2218  39356 139.9 49.2
    43.9 277 2218  39544 143.7 55.2
    44.5 274 2208  39122 142.9 51.5
    48.0 267 2151  38898 138.6 51.4
    49.6 275 2188  39114 141.7 47.8
     max 278 2154  39611 147.5 51.8
    
    ===Percentage cf Max From Log File===
    Gain Aircrf Postns usblMs maXdst aVgdst Goodness(1A+1P+1M+1X+1V/5)
    37.2  93.17 100.00  98.59  99.63  94.95  97.27
    38.6  93.53  95.80  98.49  99.17  98.54  97.11
    40.2  92.81  96.07  98.84  94.06  95.07  95.37
    42.1  95.32  97.66 100.00  94.87  90.80  95.73
    43.4  96.40  97.97  99.25  94.85  89.28  95.55
    43.9  99.64  97.97  99.73  97.38 100.00  98.94
    44.5  98.56  97.53  98.66  96.86  93.35  96.99
    48.0  96.04  95.01  98.10  93.95  93.20  95.26
    49.6  98.92  96.64  98.64  96.01  86.71  95.39
     max 100.00  95.14  99.89 100.00  93.96  97.80
    
    Best Log File Goodness: 98.94
    Restarting with best gain: 43.9
    
    Previously running with gain: max

  6. #6
    Purser
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    With a quality antenna the need for filtering is reduced anyway as it is designed to primarily receive 1090 MHz.

    Maybe the mentioned antenna is even better at that than the Flightaware antenna for example.

    I would think your weak point is the cable that is weakening the signal. (How long is your cable run?)
    If you don't have a strong signal to begin with, there is less chance for noise to be a problem at all.

    Or you are just limited by terrain which could very well be the case.

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