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Re: questions about fundamentals

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  • bearlabsusa
    ... Yeah ok, I m only interested in a fancy IF strip where my IF freq is either 455kHz. or 500kHz. ... Right, but I m only at 455kHz or so... ... Are we
    Message 1 of 16 , Mar 30, 2008
      --- In softrock40@yahoogroups.com, Jack Smith <Jack.Smith@...> wrote:
      >
      >
      > >
      > > Thanks Jack for the rundown...
      > >
      > > I'm scratching my head a bit here... but at 455kHz. it doesn't seem on
      > > the surface that all that much is required to buffer the signal going
      > > into the SRL??
      > >

      >
      > Depends. It's a lot easier to do it at 455 KHz than 73 MHz, and the
      > Z10000 is designed to work between 50 KHz and 100 MHz.

      Yeah ok, I'm only interested in a fancy "IF strip" where my IF freq is
      either 455kHz. or 500kHz.


      > > Is 70db really that good a figure?
      > >

      >
      > I think so, but I stand to be corrected. More recent measurements show
      > it's closer to 90 dB.
      > >
      > >
      > > Would not a fairly standard opamp or buffer that has the requisite
      > > bandwidth do as good a job, or nearly as good a job?
      > >

      >
      > At 455 KHz probably. Not at 73 MHz.

      Right, but I'm only at 455kHz or so...


      > > How about just a FET run as a follower - no feedback connection back
      > > to the input? That any good?
      > >

      >
      > FET source followers have issues with output impedance for most small
      > JFETs. A bipolar transistor is a better choice from this prospective.

      Are we driving something with a very low input impedance in the SRL?
      I don't know. I suppose if it is 50 ohms then yeah, a single FET will
      probably not cut the mustard.

      > > A simple resistive divider, or capacitive divider won't drop ur
      gain 6dB.?
      > >

      >
      > A capacitive or resistive divider provides no isolation to speak of.
      You
      > might be OK with a -40 dBm leakage signal being fed backwards into your
      > receiver's IF, but I'm not. It's a matter of what precautions one wants
      > to take to prevent degradation of receiver performance. I don't like
      the
      > thought of strong signals hanging around just outside the IF filter
      > bandpass. In many cases, it will be OK, but in other cases, I strongly
      > suspect it is not going to be OK.

      I meant after a buffer...
      I was wondering about the need for a special buffer that can do
      negative gains... that was my context. Sorry I wasn't clear on this point.

      >
      > >
      > > Honestly, I don't know the answers, so I ask the questions.
      > >
      > > _-_-WBear2GCR
      > >

      > I have 50 Z10000 buffer amplifiers in the hands of owners for about a
      > year and half now and so far all owners are happy with the results.
      >
      >
      > Jack K8ZOA
      > www.cliftonlaboratories.com

      Well fine Jack! :_)
      No doubt they work ok!
      But I guess it depends on your application, as to the need and/or
      appropriateness?

      As I said at the top, I'm trying to take the express lane to figure
      out how to use these things - once I get one. ;_)

      _-_-WBear2GCR
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