Re: LF: LF EbNaut test from JN80 on 137370

[Andy Talbot <andy.g4jnt@gmail.com>]

Hit send too soon on the last one

On 12 December 2015 at 12:06, Andy Talbot <andy.g4jnt@gmail.com> wrote:

I've just added a fine tune to the PC prog to shift teh input frequeny by any amount specified in a text box

           

 

  {  ipI& and ipQ& are the input samples from the receiver  }

 

            LOtheta = Val(Tuning.Text) / Fsample  

            LocalOsc = LocalOsc + LOtheta             'Both are normalised frequencies (Fsample = 1)

            LocalOsc = LocalOsc - Int(LocalOsc)      'Fractional part only

            theta = 2 * pi * LocalOsc

  

            IPData(DataPointer&, 0) = ipI& * Cos(theta) - ipQ& * Sin(theta)       '    I

            IPData(DataPointer&, 1) = ipQ& * Cos(theta) + ipI& * Sin(theta)      '   Q

The effect of that is for any positive freqeuncy in Hz intereed into Tuning.text , the spectrum plot shift positive, and conversely the display shifts wown for any -ve value entered

Andy  G4JNT

On 10 December 2015 at 20:34, Paul Nicholson <vlf0403@abelian.org> wrote:

In vlfrx-tools I use

 I = s(t) * cos( 2pi * Fo * t);

 Q = s(t) * sin( 2pi * Fo * t);

where s(t) is the incoming signal and Fo is the
local oscillator frequency.   Is that right, or
should there be a minus sign in there somewhere?

If s(t) is VO1NA at 137370.00000 and I set Fo to
137369.9, then when I put I and Q into EbNaut, it
needs an offset of +0.1 Hz to decode as you would
expect with the LO being 0.1Hz on the low side.

For more general mixing and frequency shift,
to select the upper sideband of the mixer output
I use

   I - j * Q

is that the right way round?   When I take I/Q data
from an RTL2832 I find I have to invert Q to get the
correct sideband, ie I + j * Q.   That's the only
independent source of I/Q signal that I have available
to try.

--
Paul Nicholson
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