Question regarding the Voltage Input Range

Allgemeine Themen
df5fh
Beiträge: 9
Registriert: 03 Jan 2017, 17:45

Question regarding the Voltage Input Range

Beitragvon df5fh » 02 Mai 2018, 14:54

Hello dear OMs,

I have a question regarding the input voltage of the Red Pitaya. I assume a Red Pitaya ADC input range of -1V to +1V, in other words 14 Bits for 2V.

16384 = 2000000 uV --> 1 = 122 uV

The antenna is directly connected to the ADC and a RF-Signal with S9 comes in with 50,15 uV ... In my view not enough to set Bit0 to H in the ADC-Output-Value ?
How is it possible to read weak signals in this environment ? Where is my fault ?

Vy73
Henning, DF5FH
pavel
Beiträge: 69
Registriert: 05 Mär 2016, 10:52

Re: Question regarding the Voltage Input Range

Beitragvon pavel » 02 Mai 2018, 17:37

Hello Henning,

How is it possible to read weak signals in this environment?


It depends on the bandwidth of the signal and on the presence of other signals and noises.

If you have a noiseless ADC in a noiseless environment with only one weak signal and the ADC constantly outputs zeroes, then indeed detecting the weak signal could be problematic.

If the weak signal is mixed with other signals and noises and if the bandwidth of the signal is much lower than 62.5 MHz, then some gain could be obtained from the signal averaging.

Best regards,

Pavel
df5fh
Beiträge: 9
Registriert: 03 Jan 2017, 17:45

Re: Question regarding the Voltage Input Range

Beitragvon df5fh » 03 Mai 2018, 10:53

Hello Pavel,

thank you very much for your response. This is near-miracle stuff for me and I have further questions. I heard people say that the Hermes-Board is better than the Red Pitaya because it owns a 16Bit ADC. Hmmm ... this requires that these more bits are really used. If I connect my 80m antenna with the Red Pitaya what could I expect at the digital output seen by the software? What is the maximum adc-output-value your software has to handle ? How many ADC-Bits are really toggling ? In my simple imagination I would expect that the Red-Pitaya works at maximum performance if the complete value range of the ADC is involved. I would expect that this goal can be achieved using a preamplifier ... in best case with an automatic control loop for leveling. But meanwhile I have doubts. I need enlightenment, please !

friendly regards
Henning
Uli DF5SF
Beiträge: 102
Registriert: 31 Mär 2016, 18:32

Re: Question regarding the Voltage Input Range

Beitragvon Uli DF5SF » 03 Mai 2018, 13:25

Hallo Henning,

es gibt grafierende Unterschiede zwischen SDR und Analogempfängern. Umdenken ist erforderlich.

Hierzu findest du sehr viel im Internet, z.B.:
http://www.ab4oj.com/sdr/apdxc16_sdr.pdf
http://mirror.thelifeofkenneth.com/lib/ ... dRadio.pdf

Viel Spass beim Lesen
73 de Uli, DF5SF
df5fh
Beiträge: 9
Registriert: 03 Jan 2017, 17:45

Re: Question regarding the Voltage Input Range

Beitragvon df5fh » 03 Mai 2018, 17:50

Hello Uli,
thank you for the links, I already tried those documents but while reading I feel my limits quickly :-) Think I have to try again ...
Do you have an idea about the number of bits which are used in the RP-ADC under "normal conditions" ? Actually this is of personal interest to me. What is your opinion about using a preamplifier to increase the RP-performance ?

Vy73
Henning
Uli DF5SF
Beiträge: 102
Registriert: 31 Mär 2016, 18:32

Re: Question regarding the Voltage Input Range

Beitragvon Uli DF5SF » 03 Mai 2018, 18:46

Hi Henning,

the RP uses 14 bit. The difference to 16 bit is minimal, see document from AB4OJ page 14.
At beginning I had a 1:9 unun at the input of RP. Infos here. This works fine from 80 to 20m.
Now I have a preamplifier from DC2PD, kit see here.
73 de Uli, DF5SF
df5fh
Beiträge: 9
Registriert: 03 Jan 2017, 17:45

Re: Question regarding the Voltage Input Range

Beitragvon df5fh » 04 Mai 2018, 10:18

Hello Uli,

thank you for your patience. Yesterday we had "OV-Abend" and we discussed this stuff endless. Keeping friendly and patient is very important when different opinions are expressed in a discussion :-) I made some basic faults regarding the size and influence of values.

friendly regards
Henning

Zurück zu „Allgemeines“

Wer ist online?

Mitglieder in diesem Forum: 0 Mitglieder und 1 Gast