RX and TX with a big dish (1.8m) without kill the lnb !!!

  • Good evening,

    I have a question , I want to use this setup :

    - Dual band feed DJ7GP with lnb octagon

    - PA 4W

    on a 1.8m dish. But I wonder about the insulation of the lnb when I transmit. Does the high power of 2.4 Ghz can create fatal harmonics for the 10Ghz lnb and kill it ?


    Chris, F4FLU

    • Official Post

    Obviously, the 2.4 GHz itself cannot enter the LNB due to waveguide cutoff. 4x2.4 GHz = 9.6 GHz, which is a theoretical possibility.

    But assuming you stick to the legal power limit on 13cm and drive the final amplifier not too recklessly, the harmonics should be far below any danger limits for the LNB. You want to use a 4 W amplifier presumably for SSB so you would need to back off a bit anyways. And then, I don't think harmonics are a problem.

    Have fun!

  • fifth harmonic is 12ghz (5x2.4) and can desense (with lower power) or kill the lnbs first transistor stage

    and 12 ghz is easy travvelling inside the waveguide (its build for 11 to 12ghz .. not?!)

    an overdriven and clipping amp produces higher fifth overtone

    so stay low in power and stay linear (plus a lowpass filter inside or behind amp)

    that lowers the signal on 12ghz that otherwise... see above