Message-ID: <003d01c1b971$bb884ec0$6a01a8c0@cianciolo>
From: "PC" <paulc@snet.net>
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$6a01a8c0@cianciolo> <000401c1b96e$e5ac4ce0$1700a8c0@home>
Subject: LF: Re: Re: Re: Re: Vectorscope display
Date: Tue, 19 Feb 2002 13:17:46 -0500
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Thank you Dave!!

Paul W1VLF


----- Original Message -----
From: "Dave Pick" <g3yxm@wireless.org.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, February 19, 2002 12:57 PM
Subject: LF: Re: Re: Re: Vectorscope display


>
> 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
> > >
> > >
> > >
> >
> >
> >
>
>
>