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Re: [Xylo-SDR] Janus board block diagram



Phil,

Completely agreed! My final target is the stand-alone ADC, DDC, DSP
combination for the RX and ADC, DUC, DAC for the TX. Still I want to see
how far the SDR-1000 concept can be pushed with better QSD, lower
spurious DDS, and higher dynamic range ADC. This means that the work of
both Phils will be necessary for me.

Both of you, continue with your great innovations. You know best what
you want and go ahead. Don't let us "lurkers" frustrate yourself with
our excessive desires.

73, Ahti OH2RZ


----- Original Message ----- From: "Phil Harman" <pvharman@arach.net.au>
To: "Xylo-SDR Discussion" <xylo-sdr@lists.ae5k.us>
Sent: Wednesday, January 25, 2006 2:31 PM
Subject: Re: [Xylo-SDR] Janus board block diagram


Hi Ahti,

Initially the Janus board will simply act as a USB sound card that you
can
connect the outputs of the SDR1000 INA163's to.

I intend to keep the inputs to the WM8785 (or PCM2402) at high level
to
maintain the S/N ratio at their input so had not intended connecting
the QSD
capacitors directly to it.  I'm not sure that would work without
additional
gain anyway but if not we could always use a higher performance
amplifier
(with differential outputs) than the INA163.

In fact at the moment I don't intend to use a QSD at all. We still
have not
found a way to overcome the serious noise figure problem of the QSD
above
about 18MHz and the  current theory says its not fixable.

I have breadboarded a new bus switch based mixer designed by I7SWX and
that
works up to 70MHz without any NF problems.  It does have a conversion
loss
of ~6dB so we will need to follow it with a low noise audio pre-amp
ahead of
the A/D converter.

It seems to me that we need to feed these pre-amps at a much higher
impedance than 50 ohms in order to achieve the NF they are specified
at. My
idea at the moment is to follow the mixer with a step-up audio
transformer
and fix any phase shift issues with software.  My previous experience
with
such transformers is they tend to pick up all sorts of hum and noise
so some
experimentation is required.

I really hope Phil C's idea of using a LTC2208 high  speed A/D
converter
works and we can then ignore these mixers altogether. Plenty to do and
lots
of fun to be had!

73's  Phil....VK6APH


----- Original Message ----- From: "Ahti Aintila" <ahti@attocon.com>
To: "Xylo-SDR Discussion" <xylo-sdr@lists.ae5k.us>
Sent: Wednesday, January 25, 2006 3:03 PM
Subject: Re: [Xylo-SDR] Janus board block diagram


Phil,

Thanks! Looks good.
Do you intend to connect WM8785 directly to the QSD capacitors
without
any buffer opamps in between? (I hate the INA163.)

73, Ahti OH2RZ

----- Original Message ----- From: <pvharman@arach.net.au>
To: "Xylo-SDR Discussion" <xylo-sdr@lists.ae5k.us>
Sent: Wednesday, January 25, 2006 8:28 AM
Subject: Re: [Xylo-SDR] Janus board block diagram


OK - the Janus block diagram is on www.hamsdr.com in the public
folders area
in the directory Janus. Is in both Visio and GIF forms.

Let the feedback begin!

Phil...VK6APH