Really low sample rates for gr_sig_source_x()

GNU Radio
1

It looks like when you set low sample rates (say below 1KHz), the NCO
code doesn’t seem to work right,
never putting out samples.

I haven’t done exhaustive testing.

This was prompted by Bill Pretty’s issue with his flow-graph that uses a
triangle or sawtooth generator,
at low sample rates (2Hz) and low Fc (a fraction of a Hz) to drive the
tuning variable going back into
the USRP.

I tested the graph he gave, and after making a few fixes, observed that
the signal source appeared to be
never producing any output. Hmmmm.

So, I did up my own flow-graph, consisting of a signal source, a
throttle, and a number sink and scope.
It only started to work when I cranked the sample rate up to about
1KHz on the signal source.

Any ideas?

–
Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

2

On Sat, May 08, 2010 at 06:13:15PM -0400, Marcus D. Leech wrote:

the USRP.
Any ideas?
Does it work without the throttle?

Eric

3

On Sun, May 9, 2010 at 11:33 PM, Eric B. [email protected] wrote:

tuning variable going back into

Any ideas?

Does it work without the throttle?

Eric

I just tested it in GR with sig_source → throttle → scope sink.

I set the sample rate to 10 and the frequency of the signal to 1. It
took a while, but it eventually plotted output. I then used the 10 as
the sample rate for the signal source and 10k for the rate of the
throttle and it worked with results coming in much faster.

I think it’s working as it should.

Tom

4

On Sun, May 9, 2010 at 11:33 PM, Eric B. [email protected] wrote:

I just tested it in GR with sig_source → throttle → scope sink. I
set the sample rate to 10 and the frequency of the signal to 1. It
took a while, but it eventually plotted output. I then used the 10 as
the sample rate for the signal source and 10k for the rate of the
throttle and it worked with results coming in much faster. I think
it’s working as it should. Tom
So perhaps I misunderstand two things:

o how throttle works
o how number sink works

Does number sink produce a new display on every sample?

How does throttle “do its thing” exactly?

–
Marcus L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium