[hpsdr] Janus frequency response ?

[Ahti Aintila]

David,

That was an easy solution. I shorted the resistors, too. When going to
the differentian input, you need to move jumpers J1 and J4 to the
lower position.

If you now want to increase the dynamic range and lower the
amplification, you might take the I/Q signals out from the SDR-1000 in
differential form directly from the sampling capacitors. Look at the
HPSDR Archives (May and June) for my messages (author Ahti Aintila)
having subjects including "JanOz-163" and "NOISE and Janus".

Be careful though with the soldering of the cable. Check also that you
never let the signal go more than 2.5 Vpp to the input of the AK5394A.

I do not recommend any shorter time constant for the QSD. If you need
a flat frequency response for any broadband applications with 192 kHz
sampling, software correction might be the better way.

73, Ahti OH2RZ


On 05/06/07, David Woodhead <dwoodhead at bms-inc.com> wrote:
> Ahti,
>
> I figured out the problem. The Janus board input has series resistors
> (39K) to lower the signal level from the SDR1000. These are followed by
> emi filters which = 1000pF to ground. The combination is a nice LPF!
> Shorting the series resistors fixed the problem and resulted in a nice
> flat noise spectrum with just a few dB roll off on the edges (same as
> Delta 44). Ofcourse the gain is too high now so I must come up with a
> better solution. I plan to drive the A/D with a differential signal
> (presently I'm only driving it on one side) which should improve the
> dynamic range a little. I'm not sure this is new information - I just
> didn't pay attention to it first time around.
>
> I wonder if anybody has experimented with different LPF values on the
> QSD for 192KHz sampling?
>
> 73's
>
> David.
> KM5TZ
>
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