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Re: BPF coils

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  • ve3poa
    Thanks Bob for the answer. When I wound the coils there were only a couple that I took some windings off in order to bring the inductance closer to the
    Message 1 of 26 , Oct 27, 2009
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      Thanks Bob for the answer. When I wound the coils there were only a couple that I took some windings off in order to bring the inductance closer to the required value. In the practical sense, your right, who would have noticed the difference. However in the theoretical world it became a curiosity.

      73, Peter
      ve3poa

      --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@...> wrote:
      >
      > Hi Peter,
      >
      > Sorry, I realised I did not actually answer your question.
      >
      > People get too hung up worried about the measurement frequency and the effect that it will have on the inductance measured. Yes it does, but does it really matter?
      >
      > Lifes as complicated as you want to make it!
      >
      > All I can say is, I wound the inductors as per the drawings, and then measured them, and they were well within what I would personally think is acceptable given all the variables involved.
      >
      > Anything better than 10% is not worth worrying about, particularly as the capacitors used in the tuned circuits I believe are at best only 10%.
      >
      > 73, Bob G8VOI
      >
      >
      > --- In softrock40@yahoogroups.com, "ve3poa" <ve3poa@> wrote:
      > >
      > > So after all this discussion, what is the short answer?
      > >
      > > When is the LC meter accurate and where might you have to take into account inaccuracies? In other words, it's accurate below xx mhz. and off by so much above. Or is to complex to be able to make such a simple rule of thumb?
      > >
      > > 73, Peter
      > > ve3poa
      > >
      > > --- In softrock40@yahoogroups.com, "g8voip" <g8voi.reeves59@> wrote:
      > > >
      > > > Hi,
      > > >
      > > > I do not really want to get involved, but...
      > > >
      > > > The L/C meter being talked about works on the principal of an oscillator where the frequency is dependant on the value of a known internal fixed value inductor and precision capacitor.
      > > >
      > > > A calibration is performed with the input leads shorted, so the oscillator runs at a particular frequency which can be measured, and takes into account inductance contributed by the test leads.
      > > >
      > > > You then insert your 'unknown' inductor in series with the reference inductor and measure the new oscillator frequency.
      > > >
      > > > Knowing the two oscillator frequencies, and the value of the reference inductor, you can calculate the 'unknown' inductor value.
      > > >
      > > > The meter I use is a varient of that design, via a VK website, and a 'dual range' version by Cristi Morariu.
      > > >
      > > > As part of the calibration and checking process, I measured a very large number of inductors (100+), and averaged out the errors.
      > > >
      > > > With all of the SoftRock inductors I have wound, the vast majority have been within 10% of the nominal started value when winding just by the number of turns recommended. Worse cases have only needed one or two turns adding or removing to get them spot on.
      > > >
      > > > Hope that clarifies it :)
      > > >
      > > > 73, Bob G8VOI
      > > >
      > >
      >
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