Re: psk characters speed


Craig AC4M
 

Some of it is due to no education about QPSK other reason could be due to hams resist change in general, it hard to know the difference by the sound and look (which I can hear the difference and see the difference), BPSK31 is usually the default mode, Not a huge difference in actually performance due to phase noise, QPSK is side band dependent some people on BPSK might be in LSB or USB.

Another side note I think QPSK modulation technique is a little more behaved compared to BPSK (meaning not as wide banded like BPSK can be maybe that is due to the energy being spread out more in the phases instead of just two phases which there is slight penalty compared to BPSK, but the soft decision brings it back up near BPSK levels for sensitivity)

--- In 070@..., David Westbrook wrote:

thanks steve!

If the rate is the same, and QPSK provides FEC (forward error correctrion)
for robust decodes, why isn't it used more?

Is is because of the latency? (from wiki) "To successfully decode an
input bit requires a large number of phase shift sequences to be received,
causing a 20 bit, 640 millisecond latency (delay) in the output of the
decoder"
Or because we just d_n't r_a_ly n__d 10_% cp_ to un_ers__d th_ m___age?
Or other (historical/etc) reasons?

--david
kj4izw



On Mon, Jan 7, 2013 at 10:00 AM, melachri wrote:

**



===> I'm looking for someone more knowledgeable than me about the inner
workings of the BPSK31 mode to verify the calculations...
I based it one the varicode length (from Wikipedia) plus '00' between
characters, and 32ms per bit.
I didn't check your lookup table, but the 00 delimiter and 32 ms per bit
parameters are correct.

And FWIW, it's the same for QPSK31. Although QPSK encodes two bits per
modulation symbol, the rate-1/2 convolutional code exactly compensates,
making the character rate identical.

Steve
W3HF



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