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Thread: LNA Issue

  1. #1
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    LNA Issue

    Hi all,
    In order to improve my range, I bought this week a Low Noise Amplifier SPF5189Z.
    It's a 5V amplifier and I connected it to pin n2 and 14 of my GPIO raspberry pi. Pins n 4 and 6 are dedicated to the Fan.
    When I try this following configuration, I have no signal:
    Antenna - 5m SMA Cable - LNA - SMA to MCX adapter - DVB T dongle - Raspberry Pi.
    Without the LNA, everything is fine with 250 messages per second.
    Do you have any idea of what may be the issue ?
    Thanks.

  2. #2
    Captain
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    Apr 2018
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    Have you tried lowering the gain?

    Also unfiltered amplifiers can amplify noise which can lead to the dongle not receiving anything anymore.
    Last edited by wiedehopf; 2019-05-30 at 22:44.

  3. #3
    First officer
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    The SPF5189Z device is a broadband amplifier reportedly covering the range 50 to 4000MHz, which also leads me to suggest overloading of the receiver with a range of nearby sources.

  4. #4
    Purser
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    reportedly covering the range 50 to 4000MHz
    In my early radio days, this would have qualified as .. dc to daylight

  5. #5
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    Quote Originally Posted by ylis View Post
    In my early radio days, this would have qualified as .. dc to daylight
    Or as wide as a five bar gate.

  6. #6
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    Quote Originally Posted by Stealth View Post
    Or as wide as a five bar gate.


    Thanks for your quick answers guys. I was not expecting a negative effect of the amplifier but it is true that around Paris I may be exposed to a lot a sources causing noise in my case.
    I will try to have a look at raw signals with and without to confirm that and check the health of the component, waiting for my filter.
    I will of course share the results.

  7. #7
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    Quote Originally Posted by flyghost View Post


    Thanks for your quick answers guys. I was not expecting a negative effect of the amplifier but it is true that around Paris I may be exposed to a lot a sources causing noise in my case.
    I will try to have a look at raw signals with and without to confirm that and check the health of the component, waiting for my filter.
    I will of course share the results.
    To give a practical example. The Flightaware stick that I used to use had both an amplifier and a filter built in, but if I didn't add in a SAW band-pass filter I received only aircraft that were very nearby, due to overloading of the stick by cellphone and other signals. With the filter in place I was receiving in some directions to 400+ km.

  8. #8
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    I performed some test with the help of GQRX.
    I used a 15m SMA cable for this test. Instead, I cruise with a 5m SMA cable.

    Below is the illustration of the initial topic :
    FR24 Feed without LNA FR24 Feed with LNA
    2019-05-31_1518.jpg 2019-05-31_1521.jpg

    I looked at a typical radio frequency, and I can directly see the effect of the amplifier. Amplitude gains 20db as specified by this LNA. It makes me conclude that this LNA is working properly:
    Radio Fr. without LNA Radio Fr. with LNA
    2019-05-31_1651.jpg 2019-05-31_1653.jpg

    However, I looked at the 1090MHz frequency and I have the same signal with LNA, without LNA and without Antenna.
    2019-05-31_1728.jpg

    I will then wait for the filter and performed the complementary tests.

  9. #9
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    Hey everyone,
    I just received my filter. Plugged in and here is the result :
    2019-06-11_1952.jpg
    Thanks for your help.

  10. #10
    Captain abcd567's Avatar
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    Glad to know your problem is solved.

    By the way, your map without filter was dark with water marks "for development purposes only".
    With filter it became bright, and no water marks.
    Seems adding the filter has improved the map display also

    Quote Originally Posted by flyghost View Post
    Below is the illustration of the initial topic :
    FR24 Feed without LNA FR24 Feed with LNA
    2019-05-31_1518.jpg 2019-05-31_1521.jpg
    Quote Originally Posted by flyghost View Post
    Hey everyone,
    I just received my filter. Plugged in and here is the result :
    2019-06-11_1952.jpg
    Thanks for your help.

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