[Linrad] Re: Giving up on SDR-IQ and Moving to Sound Card

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Thomas,

> I am sort of giving up on the SDR-IQ.
Why?

From what you wrote before it works ok.
I do think you will get better dynamic performance with a soundcard,
but most probably you do not need a high dynamic range and then it 
does not matter.

> I plan to connect an amplifier to the loop in to my sound card.
Or into the SDR-IQ:-)

> I have searched for the spec for the sound built into the motherboard,
> but, the results are too big for me to find it, yet.  I am still
> looking.
> 
> I have never played with audio on any computer system. I understand the
> hardware in a general sense. However, I see two audio devices,
> 
> > lspci | grep -i audio
Oooh! You are a Linux Guru:-)
Never seen this way of getting sound info before...
 
> 00:1b.0 Audio device: Intel Corporation 82801JI (ICH10 Family) HD Audio
> Controller
> 01:00.1 Audio device: ATI Technologies Inc RV620 Audio device [Radeon HD
> 34xx
> Series]
> 
> > lshw -class multimedia
This command is not available on my Linux system...

> *-multimedia
> description: Audio device
> product: RV620 Audio device [Radeon HD 34xx Series]
> vendor: ATI Technologies Inc
> physical id: 0.1
> bus info: pci@xxxx:01:00.1
> version: 00
> width: 64 bits
> clock: 33MHz
> capabilities: pm pciexpress msi bus_master cap_list
> configuration: driver=HDA Intel latency=0 module=snd_hda_intel
> *-multimedia
> description: Audio device
> product: 82801JI (ICH10 Family) HD Audio Controller
> vendor: Intel Corporation
> physical id: 1b
> bus info: pci@xxxx:00:1b.0
> version: 00
> width: 64 bits
> clock: 33MHz
> capabilities: pm msi pciexpress bus_master cap_list
> configuration: driver=HDA Intel latency=0 module=snd_hda_intel
> 
> Looks like these are the same device?
I have no idea, but yes, that seems likely.

> > xlinrad
> U
> A
> And, I see
> Dev device sample-rate channels bytes modes
> no file min/max
> ---- ------- ----------- ------- ---- ----------------
> 63 /dev/dsp 1000/192000 1 2 4 1 2 RDONLY WRONLY RDWR
> 
> Is the max sampling rate really 192KHz???
That is what the ALSA-oss answers when Linrad asks for device
capabilities. Unfortunately ALSA-oss does not tell the truth, 
the device is probably fixed at 48 kHz, but ALSA-oss will convert
to any speed between 1000 and 192000 if you ask for that (which
would be silly) When using ALSA-oss as well as when using Microsoft
Windows one has to know the native capabilities of the hardware
used because the operating system pretends that it has hardware
that can do any speed you ask for. You might use native ALSA or
4Front OSS to see what hardware capabilities you actually have.

> I select this (only) device
> 
> Not RDWR
Yes.

> If I select sampling speed as 192000, I get an error later, stating the
> sampling speed is > 190078
> So, I enter sampling speed 190078
Press 'T' to get timing info. Maybe the error is just happening once
in the start up phase and that 192000 is available afterwards.

> Then, I have a choice of 4 items
> 1 One rx channel (normal audio)
> 2 One rx channel I/Q
> 3 Two rx channels (adaptive polarization/phasing)
> 4 Two rx channels I/Q (adaptive polarization/phasing)
> 
> I choose 1. But, I would like to get I/Q. What do I need for this?
You wrote you want to look at 0.1 to 48 kHz. Your builtin soundcard is
probably sampling at 48 kHz so you would not see more than 0.001 to 
about 22 kHz. The signals you see above would be corrupted by aliases.

To get I and Q you would have to build an analog mixer with two channels.
One fed with an LO of e.g 22 kHz, the other with the same LO but twisted 
90 degrees. The output of the two mixers would go to two soundcard
inputs to give you twice the bandwidth (centered at the LO frewquency.)

I am quite a bit behind in my processing of E-mails because it has taken
some time to correct various things in Linrad that became visible with
the unforseen parameters that you selected. Linrad-03.06 will print
"overrun error" rather than an error message when there is an USB problem
(hopefully) The F1 help/mouse problem is fixed, but I have not yet looked 
at the clear_baseb bug, it is the next thing on my priority list.

The next version, linrad-03.06 will be available as soon as I found 
a solution (or decided that I can not find one now.) I would appreciate
if you could try it the same way as you did with 03-05b. You proveded
mure useful feedback in a a couple of days than I usually get in many
months.....

> In general, how much gain do I need in front of the sound card?
I guess that depends on your antenna. The soundcard is a high
impedance input and your antenna is presumably not matching it at all.
Perhaps you could use a transformer - but an amplifier is probably
easier.

  Regards

  Leif / SM5BSZ


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