[hpsdr] CW operation

[Jeremy McDermond]

On Jan 7, 2011, at 4:28 AM, Luke Steele wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi Murray,
> I have connected the paddle to Magister's DB-9 connector, so I don't think
> serial port drivers feature here.

Remember that there's a low limit on the responsiveness of the paddle connected to the DB-9 based on the sample rate.  The PTT/DOT/DASH bits are sent in the header of the packet coming in over USB.  How fast those packets come in depends on the sample rate you are using, because they're fixed at 63 samples per packet.  My back of the envelope calculations are:

48000 samples/sec:   1.2msec
96000 samples/sec:   0.66 msec
192000 samples/sec: 0.33 msec

I'm not saying that those are unacceptable, or that they're causing your problem, but it's something to consider when we're talking about latency.

Also consider on the other end of things that Penelope is always at a 48000 samples/sec rate.  You have to queue up 63 samples before you even get to send the packet across the USB.  So you could potentially have another 1.2 msec before the first sample of your CW signal gets across the USB to Magister.

I'm not sure what you're meaning by "low tens" of milliseconds latency.  If you're meaning "between 10-15", then consider that 20-25% of that latency is merely USB protocol overhead both ways.  You'll encounter the same overhead if you use Mercury's audio output because those samples get back in the same packet that the Penelope transmit samples do.  You could try to push the audio out the system speakers, but there's not telling how much latency there is in that audio device.

If you're meaning in the 10-50 range, there may be some things that could be done.  I'm not the PowerSDR guy, and in fact I'm the evil Mac guy who hasn't even bothered to write the CW oscillator in Heterodyne yet because he isn't a CW operator.  I just wanted to point out the latency inherent in the system so that you could get an idea about lower bounds.

> 73,
> Luke

--
Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj at xenotropic.com




 1294404939.0