Re: Linrad Block Diagram

[VK2KU <clearmail.com.au; vk2ku@xxxxxxxxxxxxxxxx>]

Hi Leif,

> Try to change "Parport Address" to 888. This is a bug,
> a flag that says there is hardware on the system is not properly
> initiated. Cheating this way should help to get freq and gain
> controls for sdr-14 to work. (will be corrected for 02-41)

I tried that on v2.40. It didn't work for me.
I am happy to continue with v2.39 until v2.41 is out.

> In the A/D D/A setup you have not specified
> "Select direct input"

No, the SDR-IQ has no option for Direct Input, and that question
does not appear. My stuff is directed only at the SDR-IQ.

> The "RCF Output Shift" is very large....
> The signal level required to turn on the red LED for
> A/D overload is +5dBm. At +4 dBm, the amplitude
> margin on the Linrad input is 9.55 dB which means that
> the RCF Output shift is one bit too large. (At least.)

The SDR-IQ appears to be different!
At maximum gain (0dB set in Linrad), A/D overload occurs at a SigGen
input level of -23dBm, whereas -24dB is ok.
(Measurements at the end of about 20m of RG223 at 28.1MHz).

At -24dB in and max gain with RCF shift=6 bits,
signal peak is at 114dB on  main spectrum,
noise floor (SigGen still on) is 19dB,
A/D margin is 9.15dB (as you noted above),
and with SigGen off noise floor falls to 9dB, so there is SigGen
noise!

At -24dBm in and max gain with RCF shift changed to 5 bits,
signal peak is at 120dB on  main spectrum,
noise floor (SigGen still on) is 25dB,
A/D margin is down to 3.12dB,
and with SigGen off noise floor falls to 14dB.

With the whole receive system connected to the SDR-IQ,
RCF output shift at the lower value of 5 bits,
and gain set to my usual level of -9dB (attenuator not in),
noise floor from antenna is at 29dB,
preamp turned off reduces this to 13dB,
and disconnecting transverter from SDR-IQ input drops this to 9dB.

Note that if I reduce the "gain" to -10dB,
the -10dB attenuator kicks in and the internal preamp gain of the SDR-
IQ rises by 9dB,
the noise floors are then 27, 15, 14dB respectively.
So the -10dB attenuator in the SDR-IQ lowers the noise drop from 16 to
12dB
when the preamp is switched off.


> Use "I=Soundcard test mode" to see the digital input
> that Linrad receives. (use a normal mode to set
> frequency and gain first) With the '+' button you can
> increase the gain until you see the individual bits.

I tried this, but didn't really understand how to interpret the
display,
which said A/D Max ~4000, A/D Min ~-4000.

73  Guy


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LINRADDARNIL