[hpsdr] MW DXpedition Ozy/Janus/Atlas Comments

[Ahti Aintila]

Hi Phil, Ramakrishnan and Guy,

First of all, thanks to Phil for the great design success of the Janus
board, to Guy the welcome report from the field and valuable private
comments from Ramakrishnan when estimating the noise levels.

My measurements of Janus with balanced inputs and bypassed INA163 are
not necessarily correct due to some common mode interference of the
power supply I have in my shack. In any case they indicate too low
gain before the Janus ADC, perhaps some 10 dB of more gain would be
needed for upper HF bands, quiet environment and low noise/weak signal
ionospheric conditions.

Based on the specified 123 dB dynamic (blocking) range of AK5394A, we
may calculate 20 ENOB for the ADC. That translates roughly to 20 dB
noise figure as referred to 50 ohm input and zero gain before the ADC.
Is that about right, Phil? Or did I miss something?

I have to agree with Guy that at least in my test arrangement and
layout I got very high spurious level that disturbed the MW listening.

Guy's question:
"Ahti or anyone else-- if you have suggestions on improving the signal
levels with the *balanced* connection, I would love to hear your ideas"

What to do? Perhaps slightly improved QSD (including less phase noise
of the DDS output), more preamplifier gain, less switching noise of
power supplies and careful shielding of the balanced I/Q lines. Hard
work in any case!

73, Ahti OH2RZ


On 22/09/2007, Phil Harman <phil at pharman.org> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> > What were your JP1, JP4, JP3 and JP6 status? Were the jumpers set or
> > were they open? They should be open for balanced input. Input is
> > applied at J2. (Phil, correct me if I am wrong).
> >
> Hi Ramakrishnan,
>
> Your jumper settings and input are correct.
>
> 73's Phil...VK6APH
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