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

[Nico Palermo]

> ***** High Performance Software Defined Radio Discussion List *****

> The IP3 number is probably related to the use of the TI THS4509 ADC
> driver.  It also has a rated NF of 17.1 dB.
>
> I also wonder why he chose the LTC2206-14 over the 16 bit part...  The
> LTC2206-16 is $96 in single quantity and the LTC2206-14 is $30 less...
> maybe that's it?
>
> 73 Phil N8VB

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.

>> Price is about $1072  (799 EUR)

Unfortunately for us in the European Community we have to pay a tax which
is called VAT (value added tax) and amounts to 20 % of the total. When we
export good outside Europe this tax don't apply, so the receiver price
outside EC is 666 Euros or about 892 USD.
I will make this more clear on the Perseus home page.
Sorry for the misunderstanding.

> 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

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