[hpsdr] More Mercury

[Robert McGwier]

Phil:

Thanks for the shot (after I finally figured out the extension).  I 
managed to misname the file TWICE trying to add .jpg. 

You can definitely see the CIC shape.   I propose that you replace it 
with halfband filters for a much flatter response (after you get some 
rest!).

Bob



Phil Harman wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> I've been able to interface the LT2208 demo board to the Xylo and hence to 
> PowerSDR. The screen shot at
>
> http://www.hamsdr.com/dnld.aspx?id=328
>
> show a +10dBm signal at 25MHz directly into the LT2208.  With the image 
> amplitude and phase controls at 0 and 0 respectively there is no visible 
> image.
>
> The FPGA interface to the LT2208 is very crude at the moment. I've using a 
> fixed NCO at 25MHz followed by a CIC filter decimating by 2048 since this 
> gives ~48kHz from the 100MHz clock. You can see the sinx/x shape of the 
> noise floor, the CIC needs following with a compensating FIR to flatten 
> this.
>
> The CIC is also very simple, this is the design file from MatLab
>
> // Discrete-Time FIR Multirate Filter (real)
> // -----------------------------------------
> // Filter Structure        : Cascaded Integrator-Comb Decimator
> // Decimation Factor       : 2048
> // Differential Delay      : 1
> // Number of Sections      : 3
>
> I've chosen the input frequency on the screen shot to get rid of all of the 
> spurs - there are still lots of them but I guess a better CIC and FIR will 
> clean a lot of them up.  The bandscope vertical scale is wrong since I am 
> sending 16 bits from the LT2208 and PowerSDR is expecting 24. Still it 
> lools like we are getting the full 16 bits from the LT2208 since you can see 
> about 96dB of DR.  What is intersting is that with no signal input the 
> output from the LT2208 is 0, the LSB never moves, so the internal noise 
> looks very good.
>
> We are going to need a decent pre-amp for the high bands but even so the 
> initial results look quite good.
>
> Must sleep!!
>
> 73's Phil...VK6APH
>
>
>
>
>   


-- 
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity.  Guilty as charged!


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