Message-ID: <000401c1b96e$e5ac4ce0$1700a8c0@home>
From: "Dave Pick" <g3yxm@wireless.org.uk>
To: rsgb_lf_group@blacksheep.org
References: <5.1.0.14.0.20020218184622.00aafa88@gemini.herts.ac.uk> <5.1.0.14.0.20020219140019.00ac1d70@gemini.herts.ac.uk> <001901c1b962$0e9eb460$6a01a8c0@cianciolo>
Subject: LF: Re: Re: Re: Vectorscope display
Date: Tue, 19 Feb 2002 17:57:28 -0000
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It's now at http://www.wireless.org.uk/XY.htm

Dave G3YXM.


> Hello Jim,
>
> I did not receive an email with the circuit attached and was not able to
> locate it.
>
> Could I bother you to resend
>
> Thank you
>
> W1VLF
> ----- Original Message -----
> From: "James Moritz" <j.r.moritz@herts.ac.uk>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Tuesday, February 19, 2002 10:07 AM
> Subject: LF: Re: Vectorscope display
>
>
> > Dear LF Group,
> >
> > I had the usual crop of bouncing e-mails, but I hope I have now sent the
> > vectorscope circuit to all who have requested it. Thanks to G3YXM for
> > putting it on his web pages - so hopefully it will also be available
there
> > shortly. Correction - I don't seem to be able to send it to
> > sm6lkm.jbeab@swipnet.se, Johan, so perhaps you can get it from Dave's
site
> > later, or is there something else I can do?
> >
> > Re: Andy's comment:
> > ...how about
> > the next version, a direct conversion receiver generating quadrature
> signals
> > at 137kHz then having masses of low frequency gain before the X/Y plot ?
> >
> > A low noise, high gain version of the circuit would certainly be
possible,
> > but there are a number of problems to be overcome here:
> >
> > The signal spectrum at the mixer output extends to DC, so any DC offsets
> > will be amplified as well as the wanted signals. This would saturate the
> > output unless offsets could be kept down to a few uV. Even then, the
> > remaining offset would effectively be an unwanted 0Hz "carrier" in the
> > demodulated output spectrum. A related problem is that the noise figure
of
> > amplifers, etc. increases drastically at very low frequencies due to
> > flicker noise. Both these problems could be avoided by having AC
coupling,
> > but this would put a hole in the received signal spectrum around the LO
> > frequency.
> >
> > Also, if we low pass filter the I and Q channels in order to define the
> > bandwidth, any mismatches between the filters in the two channels would
> > result in errors in the phase quadrature between the 2 channels, which
> > would be a problem if good image rejection between the sidebands were
> > required in subsequent demodulation of the signal.
> >
> > I think it would probably be possible to achieve a useable result for a
> > dedicated 136kHz RX - a fairly simple bandpass filter before the mixers
> > could restrict the bandwidth to a few kHz, and some pre-mixer gain could
> be
> > applied, reducing the post mixer gain required and reducing the effects
of
> > offsets.
> >
> > Cheers, Jim Moritz
> > 73 de M0BMU
> >
> >
> >
>
>
>