Re: Softrock EMU Linrad

[Kenrad <cs.com; ke2n@xxxxxxxxxxxxxxxx>]

Well - a little more research shows that Alberto knows about this
delay, maybe you can communicate with him and put the same into a new
release of Linrad when you get around to it?

Here is what I just found over on weaksignals.com regarding Winrad 1.3
(build 13)

 - "One to four samples delay insertable on the left or on the right
channel, to accomodate for the EMU-1212M "

73

Ken


On Jan 1, 9:34 pm, Leif Asbrink <l...@xxxxxxxxxx> wrote:
> Hi Ken,
>
> > However, I understand that a direct-conversion receiver like Softrock
> > requires software to use the I and Q signals to cancel the unwanted
> > image frequency. Linrad has an option for this.
>
> > I read in another SDR forum that the EMU card has 2 or 4 clock cycles
> > of delay between the I and Q samples.
>
> I would guess that the EMU samples at something like 64*192kHz(=12.3 MHz)
> so a shift by 2 or 4 clock states would be a small phase shift on the
> decimated signal at 192 kHz.
>
> > I have found that Linrad has an IQ calibration routine that handles
> > phase/time delays in some way.
>
> > Does this take card of a card like the EMU?
>
> Yes. As far as I know, but I do not have such a card
> so I can not tell for sure. In case the time delay
> is in clock states at 192 kHz I would guess it does
> not work.
>
> > Looking at the calibration screen on Linrad I see that I am instructed
> > to connect a frequency generator - but there is no information about
> > what signal is required. More info please?
>
> http://www.sm5bsz.com/linuxdsp/iqbal/iqbal.htm
>
> You need a sine-wave that is reasonable staple. Feed it into
> your system and make it strong in the receive mode which
> you want to calibrate. Then go to the cal screen and you
> will see something similar plus messages whether it is too
> strong or too weak (or not stable enough)
>
>   73
>
>   Leif / SM5BSZ
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