RF output control

Discussion in 'Wireless & RF Design' started by Synaps3, Oct 30, 2013.

  1. Synaps3

    Thread Starter Member

    Jun 5, 2013
    So I have a 1W RF exciter that is fed into an amplifier. I want to be able to vary the RF power into the amplifier so I don't have to vary the voltage to the amplifier. The problem is, my exciter is fixed 1W. I think what I might need is an attenuator, but I'm not sure. What I want to do is build a 1W dummy load and somehow variably switch the power so that at full power it is all sent to the amp and at no power it is all sent to the dummy load. Can you tell me what I need to accomplish this? (I'm hoping it will be cheaper than this variable power supply I thought about hooking up to the amplifier.)
  2. Danm1


    Jul 19, 2010
    do you have a schematic you could post?
  3. vk6zgo

    Active Member

    Jul 21, 2012
    The easiest way to do this is with an RF switched attenuator.
    It needs to be rated to handle the full 1W continuously.
    You may find one on EBay,or build one--just Google for "RF variable attenuator".

    At say,20dB attenuation,virtually all the 1W will be dissipated in the attenuator.
  4. gootee

    Senior Member

    Apr 24, 2007
    1 Watt is 30 dBm (0 dBm being 1 milliwatt). Attenuating by 20 dB would leave 10 dBm, which is 10 milliwatts, or 1% of the original power level.

    Here are some RF step-attenuators:


  5. vk6zgo

    Active Member

    Jul 21, 2012
    Yes,I could have phrased that better.
    I was looking at it as being a negligible level,but re-reading it he wants to wind it down to "no power at all".
    He will never get to zero,but he will get close enough!:D

    I was more concerned with the fact that the first few steps of the attenuator were going to dissipate almost all of the power.
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
    if the output stage of that exciter has a seperate power lead, just drop the voltage, the power will reduce. I have used this on a Hamtronix uhf repeater transmitter to reduce the 10 watt outputto 2 watts for an available amplifier.