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Re: [softrock40] Re: softrock oscillator

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  • Tony Parks
    Hi Joe, The QSD circuit in a SoftRock will respond to signals that are either 3 times the clock in frequency or 1/3 the clocking frequency. (Response at other
    Message 1 of 7 , Apr 24 7:39 PM
      Hi Joe,

      The QSD circuit in a SoftRock will respond to signals that are either 3
      times the clock in frequency or 1/3 the clocking frequency. (Response at
      other odd harmonics/sub-harmonics also.) It sounds like the 1/3 clocking
      frequency was what you were getting with the CHU on 3.330 MHz. A BPF is
      always needed between a QSD and the antenna to reduce the response to such
      signals.

      73,
      Tony KB9YIG

      ----- Original Message -----
      From: "Joe (K9HDE)" <k9hde@...>
      To: <softrock40@yahoogroups.com>
      Sent: Monday, April 24, 2006 9:22 PM
      Subject: RE: [softrock40] Re: softrock oscillator


      > Another observation Re: fundamental and/or overtone
      >
      > Following up on Richard's observation, I was using a 40 MHz xtal in a SR40
      > with a stock input bandpass filter to listen to 10 MHz several weeks ago.
      > later that evening only WWVH is audible on 10 MHz so I was surprised when
      > another nearby, and stronger, signal turned out to be CHU on 3.330 MHz.
      >
      > As I recall, I was able to hear the SR40 osc on 13.3 MHz on another
      > receiver. 13.3 MHz divided by 4 yields a SR40 LO frequency which
      > apparently
      > allows hearing CHU at the same time.
      >
      > Is this a feature or a flaw? What is going on?
      >
      > When I get a chance, I will attempt to replicate the simultaneous WWVH-CHU
      > reception using a DDS-60 to replace to 40 MHz rock.
      >
      > Joe, K9HDE, in Chicago's Southern suburbs
      >
      > PS As an aside, has anyone noticed the audio harmonics on WWV during the
      > 1000 Hz tics?
      >
      >
      >
      >
      >> -----Original Message-----
      >> From: softrock40@yahoogroups.com
      >> [mailto:softrock40@yahoogroups.com] On Behalf Of ah6nm
      >> Sent: Monday, April 24, 2006 4:51 PM
      >> To: softrock40@yahoogroups.com
      >> Subject: [softrock40] Re: softrock oscillator
      >>
      >>
      >> Thanks Alberto - well I thought the fundamental and second harmonic
      >> would be absent, but I am sitting here with a crystal marked 30.250
      >> MHz in a softrock oscillator circuit and measureing strong output
      >> signals (both with a spectrum analyzer and a receiver) at 10.083 and
      >> 20.166 MHz. It is a "surplus" crystal - so maybe the marking of
      >> 30.250MHz doesnt tell the whole story.
      >> 73 Richard AH6NM
      >>
      >>
      >> --- In softrock40@yahoogroups.com, Alberto I2PHD <i2phd@...> wrote:
      >> >
      >> > A crystal that oscillates on its third overtone does that by
      >> subdividing its mechanical thickness in three shears, each
      >> > moving in the opposite direction wrt the adjacent ones.
      >> Electrically only the third overtone is generated, the
      >> > fundamental and the second harmonic are absent.
      >> >
      >> > 73 Alberto I2PHD
      >> > ------------------------------
      >> >
      >> > ah6nm wrote:
      >> > > I apologize if this question has come up before. It seems to me
      >> that
      >> > > the simple untuned crystal oscillator circuit in the SR40 uses
      >> what is
      >> > > probably a 3rd overtone crystal. Doesn't this mean that the
      >> > > oscillator will produce practically equal amplitude signals at
      >> the 3rd
      >> > > overtone (28.224 MHz), and also 9.408MHz and 18.816MHz. It
      >> seems like
      >> > > these additional signals present at the input to the dividers
      >> (as well
      >> > > as even higher harmonics of 9.408 MHz) would be detrimental. Is
      >> there
      >> > > any advantage to bandpass filtering the oscillator output before
      >> it is
      >> > > divided?
      >> > > Thanks
      >> > > Richard
      >> >
      >>
      >>
      >>
      >>
      >>
      >>
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