Topband: DSP and Latency

[Jim Brown]

On Wed,3/18/2015 11:06 AM, Richard (Rick) Karlquist wrote:
> There is a very straightforward fix for this latency.
> Simply use a POTS telephone line with a phone patch.
> Receive audio comes in, and CW tones go out.  At
> the remote site, a tone decoder generates key closures.
> I measured 50 ms latency on a 100 mile phone connection.
> And you never get audio glitches. 

Good system, BUT -- don't count on that 50 msec being a constant. 
Telco's routing may change at any time. And I suspect it may be digital 
in their system. Why do I say this? Roughly 25 years ago, I had a part 
time gig doing remotes for WGN Radio for their farm show, which included 
a live jazz combo. The location rotated around their rather large 
listening area (50kW on 720 kHz). We did the gig on two dialup POTS 
lines using  Dutch system that did bandsplitting to put something like 
100 - 2700 Hz on one line and 2700-5400 on the other.  It was not 
unusual for these lines to have slightly different latencies, and the 
system had the ability to delay one channel to put them in sync.

73, Jim K9YC