I can completely identify
with your problem.? Before I retired from teaching 6 years ago,
I was faced with admin people who believed the sales critters
more than the professors they were working for.
After succinctly specifying
stereo input for the laptops, I got the 'they are stereo'
feedback from admin and faculty laptops, together with the min
spec for students, came with mono - but they had a handy numeric
keypad for data entry - one of which I am still using having
bought it off-lease.
My Communications systems 1
course was then equipped with a no-name USB sound card which
worked well with a class set of Softrock 40s until I handed it
over to another professor - one day I got an urgent call to go
to the lab because the experiment was not working.
After explaining what the
'RIAA Equalisation' switch was for to the young professor who
had taken over the course, I went back to experimenting with my
Behringer UFO202 at my desk, which I still use to play with such
stuff.
I have also had some
results with their Line 2 USB for a compact box, but haven;t
been able to get rid of the mountain at the zero beat point part
of the spectrum while using it on a raspberry pi - I suspect
that is a driver problem contoured for audiophiles and for which
I have no access to support!
regards,
Nigel
Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
Skype: TILBURY2591
On 2023-12-18 18:26, Rob Frohne (KL7NA)
wrote:
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Hi Jim, et. al.,
I
am working on the software for my Electronics II class project
for next quarter.? In the past, my students designed QSD based
software defined receivers that we used to connect to Quisk
via soundcard.? The problem is lately laptops do not come with
stereo sound inputs and so a USB soundcard is needed.? Those
are always a pain to purchase, because what was available last
year is not this, or they have changed the specs to be mono
input, or something so they don't work as well as the old ones
we used to be able to get.? Every time you buy a USB
soundcard, you take a risk.? I have lost that bet in the
past.? This year I want to have the students grab the analog
signals from for I and Q with their own ADC and send them to
the host using the USB UART.? I will still have them add a 3.5
mm jack, but hopefully only for debugging.? We will be having
JLCPCB build their boards and JLCPCB has a couple interesting
audio ADCs that are a lot less expensive than a sound card.?
The 24-bit one I'm using (PCM1808) is only fifty cents and the
specs are better than the cheap soundcards I used before.? It
will be nice to get rid of the 3.5 mm audio cable between the
laptop and the SDR.? In the future, I might want to use an MCU
with WIFI like the Raspberry Pi Pico W and send the same data
over UDP so the SDR could be more remote to the host PC.? ?I
think using the USB UART is a good first step in that
direction, so at this point I am first pursuing that first.?
?I have done tests and can get 5.9 Mbps pretty easily over the?to a Linux host.? I want a 48 kHz sample rate and
for this the bandwidth I need 3. Mbps to send 64 bits for each
IQ pair (only 48 are needed, but we can use the extra 16 bits
for each pair to send acknowledgements of commands or
synchronizing data ).? I might even be able to get a 96 kHz
sample rate in the 5.9 Mbps available.?
oThe
thing I would very much like to know is where in Quisk I
should inject this I/Q sound data that is not coming from a
soundcard.? I
have the hardware.py file figured out for controlling the SDR,
but I'm looking for how the I/Q data connects to Quisk.? It
almost looked like Hermes Lite data went directly into
quisk.c, but I'm hoping there is something easier to interface
to, than the main c program, which is daunting just to read.?
??
I
have one other puzzling issue.? The actual sample rate (due to
the Raspberry Pi Pico limitations)? is 48.0460 kHz, so I will
need to discard samples or something to get the data rate to
match the more accurate soundcard sample rate.? How close do I
need to get it for Quisk to work properly?? You have a lot
more experience with sample rate matching than I do, so any
tips you have there would be appreciated.? I have some
theoretical ideas that first reconstruct the analog signals
from the sampled ones, then resample them at the correct rate,
but I suspect that is not the best option and suspect just
randomly discarding samples at the right rate might be
better.?
The
first sentence of the Quisk Docs says,? "This
is Quisk, a Software Defined Radio (SDR). You supply an
antenna and a complex (I/Q) mixer to convert the radio
spectrum to a low IF. Then send that IF to your computer using
the sound card, Ethernet or USB."?
That is exactly what I want my students to do, and I need to
minimize the software they have to worry about, because their
learning objectives are more hardware oriented, though these
days, you cannot skip the software altogether. ?
TNX & 73,
Rob
Nigel Johnson MIEEE