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When do I use my PreAmps

Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin
edited May 2020 in New Ideas
Tim reminded me about how critical the use of the PreAmp is.  When to use it and how much to use.  

We have it well written up in our knowledge base.  I highly recommend taking the time to read it and re-read it if you haven't looked at it in a few years.

73, Mike va3mw


1 votes

Open for Comments · Last Updated


  • KD0RC
    KD0RC Member, Super Elmer Moderator
    edited May 2020
    Hi Mike, I have been using this technique with a small simplification. I find that I don't need to set to 500 Hz CW and I don't need to worry about the rx settings like eq. When I start up, I just click to an open ant and adjust for the 8 - 10 dB. As propagation changes during the course of the day, I check and adjust accordingly. I also leave the WNB engaged, as that often reduces my noise floor several dB (as much as 10dB on 40 in the evening). 73, Len, KD0RC
  • Mark_WS7M
    Mark_WS7M Member ✭✭✭
    edited May 2020
    I find I've been doing this somewhat instinctively without knowing the science behind it.  I've been observing the average noise level and playing with the preamp until I find something I like.

    The part I did not do was the disconnected antenna stuff.

    Very interesting and thanks for pointing to the article.

  • Michael - N5TGL
    Michael - N5TGL Member ✭✭
    edited May 2020
    This is good stuff.  Currently I'm using my 160m inv-L as a RX antenna.  I've been having fun digging around for weak signals...not much in the way of pileups as it seems most people can't hear them.  Picking up signals on 20m at -130 is pretty awesome, and I've worked some good DX as a result.  Separate RX antennas are awesome, and the variety of Preamp gain to pick from is also fantastic.

    This also works great on the lower bands too.  Even with a rather low 80m dipole, I worked DX over the pond, just because I could hear 'em and I don't think anyone else could.  Been great fun when the QRN is low, which it was last night.
  • Brian Denley  KB1VBF
    Brian Denley KB1VBF Member ✭✭
    edited May 2020
    8-10 db measured where?
  • KD0RC
    KD0RC Member, Super Elmer Moderator
    edited May 2020
    Hi Brian, I just eyeball it using the gridlines on the spectrum display.  The right hand scale shows dBm.  I have mine zoomed so that the gridlines are 5 dB apart.  Because the preamp/attenuator is in 8 dB increments, you can't set this too finely, but close enough is good enough.

    Len, KD0RC
  • Brian Denley  KB1VBF
    Brian Denley KB1VBF Member ✭✭
    edited May 2020
    Thanks Len !
  • KD0RC
    KD0RC Member, Super Elmer Moderator
    edited May 2020
    You're welcome!
  • Alan
    Alan Member ✭✭✭✭
    edited May 2020
    Mike and All:

    OK, good read how to set the Flex RF gain on the HF bands.

    Now, what about on 70 CM (436 MHZ), with a pre-amp at the antenna, adjustable gain on the transverter, and then the Flex RF gain?

    The pre-amp at the antenna is switchable on/off and is meant to add dB at the antenna to compensate for losses in the feedline coax at 436 MHZ.

    The Transverter has an adjustable potentiometer meant for a one-time setup of the RF gain added.

    How do others use and adjust these three RF gain settings for optimum signal to noise ratio?

    Does the antenna off / on; 10db rise technique apply?  With or without the antenna pre-amp?  How is the RF gain within the transverter set?

  • Russ Ravella
    Russ Ravella Member ✭✭
    edited May 2020
    And .... Tim does it again !  Thanks Tim !

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