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Re: off topic wanted

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  • Giancarlo
    Hi Joe, thanks for your replies ... performance ... The balun core transformer is no more part of the input filter The balance will also be reflected by stable
    Message 1 of 5 , Nov 1, 2006
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      Hi Joe,

      thanks for your replies

      --- In softrock40@yahoogroups.com, "joe price" <joeprice@...> wrote:
      >
      > --- In softrock40@yahoogroups.com, Bill Dumke <billd@> wrote:
      > >
      > > Gian,
      > >
      > > How much did using the balun core transformer improve the
      performance
      > of
      > > the SoftRocks?

      The balun core transformer is no more part of the input filter

      The balance will also be reflected by stable QSD output load(s).

      > >
      > > Bill WA9PWR
      > >
      >
      > Gian,
      >
      > I'm also interested in your findings, i've tried several circuits
      > and input transformers (baluns)and notice balance is effected by the
      > input transformer.

      Nothing is perfect. Everything is a compromise ... for HF coverage
      the #43 material should be OK to maintain a balanced transformer
      configuration, particularly core #43-202
      The not twisted windings wires will reduce inductive and capacitive
      couplings and this will be in favor of balance on a wide bw.

      I'm using Flex software it relies on balance
      > (phase and amplitude) holding over over a wide range.

      I believe all the SDR softwares relies on balanced phase and
      amplitude as Flex. These software are designed (I hope) to adjust a
      larger phase and amplitude unbalance versus the one permitted by the
      hardware (see DC RX).

      A number of
      > things come into play, DDS phase error, type of QSD cicruit ect.
      > If you read the info for the SDR ZERO receiver they have done some
      > work trying to reduce these errors by using matched capacitors and
      > a Guanella transformer on the input. Since I don't have any way of
      > measuring transformer phase and amplitude balance I was looking
      > for a known commodity.

      The problems with balance are not only associated to the transformer,
      as you know.
      The most important aspect is the exact quadrature LO phasing that
      will drive the QDS (or a mixer).
      Another problem that will facilitate phasing error is the not weel
      defined and stable impedance (change of R and reactive values) that
      will unbalance the transformer.
      A third phasing error will be the not well terminated QSD output(s),
      this will have influence on the input rf bandpass filter... that will
      reflect on phasing unbalance.
      These phasing problems will be reflected also in amplitude unbalance.
      We are in a condition of a dog biting his tail ... hi

      Again have to find the best compromise. I.E: To stabilize the BPF
      output and input of transformer you may add a low gain and noise
      amplifier.
      A DDS is driving a counter or digital quadrature generator giving the
      I & Q LO signals to the QSD. If these two signals have a time
      difference of 1nS (it looks a small value, maybe) the LO phase error
      will be 0.7 degrees at 2MHz but at 30MHz the error will be of 11
      degrees that the software will have to null !
      If you have wide band scope (BW =or> 100MHz) you can check the
      transformer two secondary windings phasing. Input generator 50 ohm
      and each secondary winding Terminated on 100 ohm (T1 4T: 6T : 6T)
      On the scope you should be able to measure the time difference
      between each output RF sinewave (2 to 30MHz) and also any eventual
      amplitude difference.

      Well, these are the ideas I have ... hi

      I hope this long chat is understandable.

      73

      Gian
      I7SWX

      >
      > Joe wa9cgz
      >
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