[hpsdr] FFT latency

[Simon Brown]

Peter,

As you're interested in this side of things may I suggest
http://www.gamedev.net/page/index.html . These are IMO the very best
programmers today, interaction is a hot topic.

Simon Brown G4ELI
http://v2.sdr-radio.com

-----Original Message-----
From: Hpsdr [mailto:hpsdr-bounces at lists.openhpsdr.org] On Behalf Of G3XJP
Sent: 10 April 2015 10:55
To: hpsdr at lists.openhpsdr.org
Subject: Re: [hpsdr] FFT latency

***** High Performance Software Defined Radio Discussion List *****

FFT latency, inherent or not inherent? Who would have imagined such a simple
question would generate such a diversity of replies? Many thanks for all of
them. I conclude the answer is "YES, inherent in the use of an FFT". And so
I will continue to avoid lots of narrow FFT bins because although they might
make the Rx better, they would also make the Tx/Rx worse for what I want it
for.

Which is not CW contesting where the format, sequence and a significant part
of the content is predictable. Which is not "take it in turns to speak" QSOs
or worse, net controllers. On the complete opposite end of the spectrum
(pardon pun), a genuine conversational near-duplex VOX QSO often has more
than one person talking at the same time - but controlled and managed and
for very brief durations. Where the "brief duration" is as long as it takes
you to recognise it is happening.

This morning it took me 5 mins of DSP'ing to add a variable test delay line
in my Rx path. This is on top of what is there already. Anything more than
abt 30-40 msecs total Rx delay feels very uncomfortable - and leads to
definite and uncontrolled doubles. Maybe over time I could get used to it
because this is an operating style thing as much as anything else. But I
don't need to. For actual use purposes, you need to add in your MIC-to-ANT
Tx delay/latency as well.

BTW a barely controlled double is when somebody has to say "Sorry, I just
doubled with you. Say again." An uncontrolled (disaster) double is when they
did not even notice it happened - and you hear plenty of those on eg 40m SSB
nets. Horrible! Are the plethora of cheepo SDRs out there making it worse?
ANS = NO - because an inherent delay is not a function of how much you paid
for it. It applies to them all.

Peter G3XJP
_______________________________________________
HPSDR Discussion List
To post msg: hpsdr at openhpsdr.org
Subscription help:
http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org
HPSDR web page: http://openhpsdr.org
Archives: http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/


 1428660609.0