[Skimmertalk] Fwd: Re: Red Pitaya modifications

[Jeffrey Pawlan]

Skimmertalk list disallowed my previous emails because it was sent as 
HTML rich text rather than plain text.

Here it is again for all RP users:

It was I who wrote last Fall that putting a transformer on the input is 
a poor bandage at best.  I already have experience building and 
modifying SDR receivers to match to 50 ohms and also utilize the full 
dynamic range of the A/D converter.  The Germans are doing the same 
thing. It is published in all of the Linear Technology A/D converter 
datasheets. The ICs on the R.P. are from Linear._
___
Once the R.P. input circuit is replaced with the correct circuit, it 
will be close to 50 ohms impedance.  If the board designer is willing to 
make a proper PCB layout, it will save you considerable time and effort. 
Instead, you can do this by hand but it requires dexterity and patience. 
Make sure you use the correct transformers shown in the datasheet. You 
can wind your own on a core but it will not be as small and the 
frequency response will not be as good.

This circuit change has no important effect on the software or firmware. 
The displayed gain or signal level will be different but I doubt that 
you are using this receiver as a calibrated signal level measurement 
tool.  I do not have a R.P. nor have used one so I do not know if there 
was a way in software to change the gain of the input amplifier. If 
there was, then that is the only change to the software as the input 
amplifier will be removed so that function would do nothing.

The improvement will be between 20 and 30dB more dynamic range.

73,

Jeffrey Pawlan  WA6KBL