[hpsdr] about latency growth with HPSDR

[Steve Bunch]

Riho,

I can't answer your question exactly, but this can happen because of buffering somewhere in your sample chain, when the sampling rate of your system is slightly slower than realtime so the samples aren't being consumed as fast as they're generated.  The unread samples are saved up somewhere, and accumulate there.  I had this happening to me in an ALSA-based Linux system -- I would over time be listening several seconds behind realtime when using a USRP to listen to FM radio.  Restarting the chain will clear out the buffered data; when you restart it will grow again.  

I don't know if the Ozy/Mercury sample chain is capable of buffering this much data (someone familiar with it should be able to tell you exactly how much can be buffered there), but in my case it was in my audio system.  Unfortunately, I don't know the various Windows audio systems well enough to give you any help, but that is where I would look first.

Steve, K9SRB

On Sep 29, 2011, at 3:07 AM, Riho B., ES7AAZ wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi,
> 
> I have a program called Faros which is a beacon monitor.
> Faros gets his time sync from ntp GPS time servers.
> NCDXF network beacons have GPS dicsiplined controller
> which allows path delay calculation and Faros does it.
> 
> After 2h running I see 120ms latency growth (linear graph)
> and it's growing on. Which means that radio waves are traveling
> about one  more circle around the world. It can't be so. Restarting
> PowerSDR brings the latency back to its initial state. Exactly the same 
> effect with CWSkimmer console. It's almost same vith VAC and with
> analog audio cable.
> 
> The question is not even about latency itself or how much it is.
> The question is why's latency growing and how much it does?
>  Is it somewhere in USB connection ?  I'm Ozy user.
> 
> 
> 
> 73,
> Riho, ES7AAZ
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