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What is a passive antenna or active antenna?

  • 01-10-2012 9:31am
    #1
    swoofer
    Registered Users, Registered Users 2 Posts: 5,707 ✭✭✭


    I am reading the manual for a combi set top box and got to the bit about settings for the aerial.

    It has me confused, it says " Enable antenna power if an external passive antenna is connected otherwise set to off if an active antenna is connected."

    What is the difference and how can I tell which aerial I have?

    gbc


Comments

  • #2
    MBSnr
    Registered Users, Registered Users 2 Posts: 2,224 ✭✭✭MBSnr


    My combi box has the same option to power an aerial. As far as I understand it a standard aerial requires no power. It's only those with amplifiers builtin that require a voltage from the box (a masthead may differ and need power from a separate supply). Someone should be along soon to put us both straight!

    Anyhow I stupidly changed the power option on mine (as I like to find out what all the options do) with a standard aerial and was greeted by the smell of smoke as something burnt out. Fairly sure it was a fuse protecting the power out. Luckily the box still worked afterwards.


  • #3
    Sam Russell
    Moderators, Science, Health & Environment Moderators Posts: 20,228 Mod ✭✭✭✭Sam Russell


    The TV can output 5V DC to the antenna input to power masthead amplifiers, but if a normal, non-amplified aerial is there, these look like a short-circuit at DC. Hence the smell. I would have thought they were protected against this.

    The in-line PSU used to power masthead amps does the same job.


  • #4
    swoofer
    Registered Users, Registered Users 2 Posts: 5,707 ✭✭✭swoofer


    ok and thanks but it still confuses me. I take it I set it to off. It looks as if in europe they use aerials with built in amplifiers where as here we use masthead amplifiers powered separately.

    Sam if I had an line masthead amplifier could I power it via the box and take away the psu near tv?

    gbc


  • #5
    Sam Russell
    Moderators, Science, Health & Environment Moderators Posts: 20,228 Mod ✭✭✭✭Sam Russell


    GBCULLEN wrote: »
    ok and thanks but it still confuses me. I take it I set it to off. It looks as if in europe they use aerials with built in amplifiers where as here we use masthead amplifiers powered separately.

    Sam if I had an line masthead amplifier could I power it via the box and take away the psu near tv?

    gbc

    Yes, but most PSU units provide 12V, but the TV/box supply 5V, but most amps will work with both. Make sure you have no DC short (use a multi meter to check the resitance os the aerial cable is not low. The 75 ohms relates to the impedance at UHF, not DC.

    The PSU near the TV will block DC from the TV side anyway.


  • #6
    Sam Russell
    Moderators, Science, Health & Environment Moderators Posts: 20,228 Mod ✭✭✭✭Sam Russell


    I would think so. Check first that the cable is not short circuit with the PSU taken out.


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