+ Post New Thread
Results 1 to 3 of 3
  1. #1
    Newbie level 2
    Points: 22, Level: 1

    Join Date
    Oct 2019
    Posts
    2
    Helped
    0 / 0
    Points
    22
    Level
    1

    Ingress in coaxial at FM frequency

    Hello everyone,

    I am designing a receiver at 100MHz composed of :
    - LNA close to antenna
    - 100m of coaxial cable
    - ADC processing

    As the signal I want to capture is low (-120dBm) and the frequency plan lies into the FM range, I am worry about the ingress effect at the coax cable. So the power at the cable input (after the LNA) will be -70dBm. How can I calculate the power of an unwanted signal that the coax will capture by ingress effect ?

    My guess is to calculate the EIRP of an FM transmitter and then remove the attenuation cause by the outer insulator of the coax but I don't have the last information.

    I hope my problem is well explained.

    Thank you in advance.

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 5
    Points: 34,050, Level: 45

    Join Date
    Oct 2001
    Posts
    4,858
    Helped
    1445 / 1445
    Points
    34,050
    Level
    45

    Re: Ingress in coaxial at FM frequency

    I think your definition "ingress effect" can be given by the "shielding effectiveness" which is a characteristic mentioned in most of the (good) coax cables data sheets.
    For example the double shielded coax cable LMR400 has a shielding effectiveness of about 92dB at 500MHz.
    For comparison a standard single shielded coaxial cable has a shielding effectiveness in the range of 40dB.
    If you know the properties of the coax shielding, you can calculate somehow which is the minimum power of the unwanted signal that your system supports.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  3. #3
    Newbie level 2
    Points: 22, Level: 1

    Join Date
    Oct 2019
    Posts
    2
    Helped
    0 / 0
    Points
    22
    Level
    1

    Re: Ingress in coaxial at FM frequency

    Yes, the shielding effectiveness is the parameter I was looking for. As the coax I will use is double shielded, it will be fine.

    Thanks.



--[[ ]]--