Re: [Discuss-gnuradio] zero crossing detection. parallel inputs to USRP

[Phong Do]

>
>    - What is the maximum voltage can I feed the daughter-board through SMA
> ?
>   
Roughly 0dBm would be a safe bet.

Which translates to roughly 0.22V

There are several handy places on the web for doing conversions between
dBm and voltage:

http://www.raltron.com/cust/tools/voltage_to_dbm.asp

To pick one at random.

Assume 50 ohms impedance for all the daughtercards

In RF system design, it's usual to talk in terms of power levels rather
than voltages.  What you'll
  generally find is that for RF componentry, maximum input levels are
generally quoted in
  dBm (dB referenced to 1 milliwatt), and sometimes dbuV (dB referenced
to 1 microvolt).


-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
-----------------

Hello,

thank you for your reply.

I found this information in the forum, I think it is from Josh
"Input Full Scale on LFRX: +10dBm = 2Vpp = 1 Vpeak = 0.7 Vrms"
So I think I can feed the max voltage up to 2Vpp in LFRX, is this right ?

I want to know the max voltage just to be sure I will not kill the LFRX. The
more important thing is I want to feed the USRP exactly the frequency (about
50Hz) of the line (home) voltage ( 50 Hz, 230V in europe). Afterthat I want
to measure this frequency. 

- Do you have any ideas how can I transform the line voltage in lower
voltage of 2Vpp and get the same frequency out ?
  I think about schmitt trigger or comparator circuit can help. Do you know
some tutorial about this ?

- To measure the frequency comes USRP, I write a new block using
zero-crossing algorithm (base on howto-write-new-block). Please have a look
in my cpp code if it is wrong.

-------------
float zero[];
  int k;

  for (int i = 0; i < noutput_items; i++){
     if (in[i] = 0){
        zero[k] = i;
        k++;
     }
  }
  out = 2*(zero[k]-zero[k-1]);

  // Tell runtime system how many output items we produced.
  return noutput_items;
-----------------

http://old.nabble.com/file/p29415484/howto_frequency_ff.cc
howto_frequency_ff.cc 
http://old.nabble.com/file/p29415484/howto_frequency_ff.h
howto_frequency_ff.h 
http://old.nabble.com/file/p29415484/howto_frequency_ff.i
howto_frequency_ff.i 


I appreciate your help.
Phong

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