[hpsdr] A new entry in the direct-sampling SDR field

[Philip Covington]

Hi Nico,

On 6/20/07, Nico Palermo <nicopal at microtelecom.it> wrote:

> Hello Phil, nice to meet you.
>
> The Perseus' IP3 is referred to the recever's input and is a number which
> comes from real tests.
> The THS4509 has a rated NF of 17.1 dB only when you use it in a 50 Ohm
> system but when you work on another impedance level it improves a lot
> (and I have also been kindly thanked by TI guys when I make them note that
> their datasheet was not clear reporting the figure).
> If you examine the model of a differential op-amp with its noise sources
> you will certainly note that working with an input impedance of, let me
> say 200 Ohm, the NF is much less for the usually required gain.
> In the Perseus receveir I use a 1:2 balanced transformer to drive the
> THS4509. This trick render the THS4509 noise almost negligible and has the
> advantage that you don't need passive input networks to balance the
> amplifier. A -131 dBm measured sensivity in CW (500 Hz) with a -6dBm full
> scale would have otherwise impossible to obtain.

Very interesting... Do you know what noise figure you are getting in
this configuration?

> > I also wonder why he chose the LTC2206-14 over the 16 bit part...
>
> Because I found less convenient to pay three times more something which
> hardly would have granted a larger BDR.
> Perseus BDR is 125 dB, say one dB less with dithering enabled. I feel it
> is a good result obtained at a good cost.
>
> 73 Nico Palermo - iv3nwv

That is close to like 1/3 more I think ($96 vs $66 going by Digi-Key
prices).  Do you compare the LTC2206 16 bit part to the 14 bit part?

Looks like a nice receiver.

73 Phil N8VB

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