----- Original Message -----
Sent: Wednesday, September 12, 2012 4:39
PM
Subject: Re: LF: RE: [rsgb_lf_group] Re:
LF: slow WSPR?
Hi Graham,
LF,
wow such a flood of incoming mails...
> Well yes Joe (K) is right, BPSK is better, but needs a linear system
to transmit .... Joe (EA) has stated, he could extract another 6 dB if the
modulation system was changed ......
BPSK vs. ASK? Unfiltered PSK _can_ be sent by a nonlinear transmitter,
it's only very unfriendly to others due to the spectral sidebands from the
sharp transitions. But so is unshaped ASK!
In simple words, ASK steps from 1 to 0 wheras BPSK transitions go from +1
to -1. So with BPSK you get twice the sensitivity, along with twice the
keyclicks. If you compare ASK at a given peak power to BPSK sent at -6 dB, you
end up at same sensitivity and same clicks. Only average power for PSK would
be half (25% instead of 50%).
Phase-continuous FSK as used in WSPR is much more gentle in that respect.
There are no steps in the waveform, thus the click spectrum falls off much
more rapidly.
> WLOF is already coded and makes use of multi pass to gain s/n, but
is psk and needs a liner system ...and is not a one-pass decode system , when
the s/n is low .but at -41 dB, by what ever scale, OP32 is well into the noise
in single pass
The advantage of such a "multipass" system is that it can be adaptive to
SNR, ie. a strong signal decodes fast, and only for a weak one you have to
wait longer.
> We didn't set out to produce a low level beacon mode, it was
supposed to be a replacement for the CW key ..
Apparently Opera is functioning as a beaconing system, and nothing else.
You basically transmit one information ("I'm there"), and you get a reply by
the internet ("I see you"). Am I missing something here?
Sooner or later, someone here will surely ask that question: On the other
hand, if you are aiming for two way communication, and there is no SNR
advantage, then why would you want to replace the Morse key in the first
place?
> The Op structure allows for up to 50% loss of signal randomly along
the time line, ie first 50%, last 50% or randomly distributed
Yes with Opera's distributed and redundant coding you can chop off half
of the signal time. WSPR can do the very same stunt. Both will need more SNR
during the remaining half, at least 3 dB, probably a bit more. Even DFCW could
do it if you had sent two repetitions at double speed ;-)
> and over a real path , the Op system is able to make use of deep
variations in fading and is immure to phase and Doppler distortion.
Yes of course, on the air there are other factors than "AWGN" white
noise. Spherics and impulsive QRM have to be dealt by appropriate (preferably
wide-band) noise blanking strategies. Fading and Doppler (which is only
milliHz on LF) may have to be dealt with. But it remains to be proven that
under these conditions Op is so much superior that it can make up for the 6 dB
shortfall under lab conditions.
> But, 'the eating of the pudding is in the proof of the making'?
Stefan, last night reaching ua0aet over land, with 7 dB left in the system,
taking some big bites out of the distance records on 136
Yes, a very nice result! I can state without envy that Stefan has a good
signal, and it is going further than others. But does that really make a point
for Opera, versus any other mode?
Graham, I'm in no way against Opera mode per se. But I have to say that I
dislike the bragging.
> The best thing about the Op system is 'The number of reason's it
cannot work' :)
Hey, that's what all those perpetuum mobile inventors keep claiming
;-)
Best 73,
Markus (DF6NM)
Re: LF: RE: [rsgb_lf_group] Re: LF: slow WSPR?
Von:
Graham <
[email protected]>
Datum: Mi, 12 Sept 2012 12:24 pm
Re: LF: Fwd: Re: Ideas for a slower WSPR for the 137 khz band
Sent:
Wednesday, September 12, 2012 1:08 PM
Re: LF: RE: [rsgb_lf_group] Re: LF: slow WSPR?
Datum: Mi, 12 Sept
2012 4:16 pm
Re: LF: Fw: LOST TRACK
Datum: Mi, 12 Sept 2012 5:18 pm
...
-----Ursprüngliche Mitteilung-----
Von: Graham
<[email protected]>
An: rsgb_lf_group
<[email protected]>
Verschickt: Mi, 12 Sept 2012 4:16
pm
Betreff: Re: LF: RE: [rsgb_lf_group] Re: LF: slow WSPR?
Well its mostly a silly argument as the systems are totally different
, in terms of data processing and the operation of the decoder and the
technical level of the equipment needed to tx/rx the mode
We didn't set out to produce a low level beacon mode , it was supposed
to be a replacement for the CW key .. the longer times where as a
result of studying the various EU/VK qrsss plots and reasoning that
over 50% of the 32 min cycle could be above the decode level ... the
rest (will be) history :)
DSP and associated 'Numeric Processing' facts and fictions are very
difficult to separate , not helped by the ongoing pie fight out to
'our' west , however... so far so good !
The best thing about the Op system is 'The number of reason's it
cannot work' :)
G..
