[Hackrf-dev] feedback on lesson 1

[Michael Ossmann]

On Fri, Aug 22, 2014 at 06:08:01AM +0200, Joris wrote:
>
> Hopefully it's ok to post some feedback on the SDR lesson 1.  All in
> all I was very pleased. The format and teacher make it extremely
> accessible.

Thanks for the feedback, Joris.  I think this is a fine place for this
conversation.

> * If there are any good questions below or in the mailing list,
> perhaps they can be converted into a "FAQ" on the lesson page?

I'm making a private list of questions people are asking me, and I'll be
sure to address them in future lessons.  I do not intend to answer
questions in written form (at least until I finish the video series).

> * It might be worthwhile to refer in the same spot to the ("lesson
> 0"?) getting started documentation that exists already. I realise that
> is not strictly the point of the lesson, but it might save some people
> some frustration.

Is it not enough to link to that page in both the homework and resources
section of the lesson 1 page?

> * Low pass filter: I may have missed it, but you emphasise the effects
> for the CPU, but it's even more important for the listener (ie, no
> noise).

I'll talk a lot more about filtering in future lessons.

> * Low pass filter bis: why is the transition width 25? In playing
> around I found that 90/10, 75/25 and even 50/50 seem to work fine?

I'll talk a lot more about filtering in future lessons.  You could
probably go as low as 45/5 and have it still work.  If the cutoff is too
low, the audio will be degraded.  If the transition width is too low,
your CPU may have trouble keeping up.

> * Low pass filter vs rational resampler: It seems there is a huge cpu
> difference between doing the first decimation in the LPF vs doing
> everything in the rational resampler. (my system can fun the former
> just fine, the later is utterly unworkable). Is there no way to put
> the decimation in a separate block?

Nice observation!  I'll talk a lot more about decimation (with and
without filtering) in future lessons.

> * Perhaps it's a good idea to post a still screenshot of endpoint of
> lesson 1. Posting the GRC file might be a good idea also, although it
> might end up reducing tinkering.

There is a screenshot of the flowgraph in the homework section, and the
.grc file is posted in the resources section.

Mike