On Fri, 14 Jul 2000 [EMAIL PROTECTED] wrote:
> Before I go into a longish talk about transforms, I's, and Q's, is there
> anyone out there that regularly runs newqpsk? I'm loopback testing the
> modem on vhf fm and I get a 50% error rate.
I run it somewhat regularly... :)
Sorry that I didn't answer to your direct email, but I'm currently on a
summer cottage 200km away from home and using GSM dada is a bit
expensive. I'll reply later.
That error rate is probably due to a somewhat ugly feature of the
original modem desing. You see, after the symbol sync is acquired and the
modem switches to data mode it just starts to feed the symbols through the
(self synchronising) de-interleaver. However there is no way of knowing
when avctually the sync sequence is over and valid data starts so there is
bound to be several symbols worth of garbage at the beginning of every
transmission. There is no way of counting the _real_ FEC errors... I've
been thinking about reimplementing part of that but it'll mean that
compatibility with the original modem is broken.
> I've used the afsk1200 baud modem in the linux kernel, I've also written a
> packet modem that works with the 'newqpsk' userspace soundmodem code.
> Both the modulator and the demodulator work on the air, but they're mainly
> a learning tool.
Tom has already written modems for all the modes that the kernel driver
handles. But as you said, writing them is good way of learning.
--
Tomi Manninen Internet: [EMAIL PROTECTED]
OH2BNS AX.25: [EMAIL PROTECTED]
KP20ME04 Amprnet: [EMAIL PROTECTED]
