The best answer is NO linears at all. Not gonna happen. But, in those
countries whee no linears are allowed, things seem to work quite smoothly
and operators get out and work DX better than most people here do.
Danny Douglas N7DC
ex WN5QMX ET2US WA5UKR ET3USA
SV0WPP VS6DD N7DC/YV5 G5CTB all
DX 2-6 years each
.
QSL LOTW-buro- direct
As courtesy I upload to eQSL but if you
use that - also pls upload to LOTW
or hard card.
moderator [EMAIL PROTECTED]
moderator http://groups.yahoo.com/group/DXandTalk
----- Original Message -----
From: "Robert Meuser" <[EMAIL PROTECTED]>
To: <digitalradio@yahoogroups.com>
Sent: Saturday, March 17, 2007 10:30 AM
Subject: Re: [digitalradio] Re: MPSK vs OFDM vs MFSK for HF High Speed Data
>
> A bigger amplifier is the solution to that. It might bring some other
> amplifier technologies to the ham bands. Even with existing equipment,
> if you have a 1 KW linear, that translates to 125 watts of digital which
> is not bad at all. The actual addition of carriers is also phase
dependent.
>
> R
>
>
> Patrick Lindecker wrote:
>
> >Hello to all,
> >
> >For me, the main problem, for Hams, of the multi-carriers modulation
(OFDM...) is that the power is drastically limited (if you want to,
legitimally, keep linear):
> >
> >If you have two carriers in parallel, the mean power/max power ratio is
equal to 1/2
> >If you have three carriers in parallel, the mean power/max power ratio
is equal to 1/3
> >............................
> >when n becomes big, the ratio tends to 1/square(n) (the carriers phases
being independant, with application of the "big numbers law")
> >For example, for MT63 where you have 64 carriers in parallel, the ratio
is 1/8. You transmit only 12.5 watts with a 100 watts maximum XCVR.
> >
> >73
> >Patrick
> >
> >
> > ----- Original Message -----
> > From: Bill McLaughlin
> > To: digitalradio@yahoogroups.com
> > Sent: Saturday, March 17, 2007 3:26 AM
> > Subject: [digitalradio] Re: MPSK vs OFDM vs MFSK for HF High Speed Data
> >
> >
> > Hi Bonnie,
> >
> > Thanks for initiating this discussion:
> >
> > Throw the prospect of incremental frequency shift keying into the mix
> > for discussion; know a few are working on this mode(s)also.
> >
> > The OFDM (AM-QPSK)+6dB better SNR may or may not be an issue...it
> > depends on usage....the usual HF near LUF versus nearer MUF or
> > VHF/UHF question.
> >
> > The key may well be your comment later, "all other factors being
> > equal". Greater raw throughput seems very dependant upon S/N (we all
> > know this intuatively). You are correct, PSK overall is a known
> > quantity...QPSK abit less so.
> >
> > In a sense you have hit upon the crux of the issue....am simple so
> > bear with me. If the SNR is high enough, then higher raw throughput
> > is available. Question (well one of them) for discussion; where is
> > the threshold? Also some mitigating factors such as "robustness"
> > (never sure that has been defined) and the ever-lovable "bandwidth".
> >
> > 73,
> >
> > Bill N9DSJ
> >
> > --- In digitalradio@yahoogroups.com, "expeditionradio"
> > <[EMAIL PROTECTED]> wrote:
> > >
> > > Since there is work presently being done to advance HF data
> > > communications, I thought it would be good to start a dialogue
> > > here about the advantages of PSK signals on HF, over some of
> > > the other choices. I'm not a world expert on these particular
> > > systems, however, I have used them and have an understanding. I
> > > have also been involved in design engineering of commercial
> > > radio communications using high speed data OFDM, AM-QPSK, and
> > > MPSK on DSP platforms. I hope that some of the individuals who
> > > are working on new HF data systems and data modes will engage
> > > in this discussion.
> > >
> > > Background.
> > >
> > > PSK signals have been long proven for HF communications.
> > > The MIL STD 188-110 type PSK signals have been in constant use by
> > > government and other entities for HF data and email, and they are
> > > now being adopted by hams.
> > >
> > > The standard 188-110 "serial tone" modem is an example of a
> > > Multi-Phase PSK signal (8PSK) running at a phase shift symbol rate
> > of
> > > 2400 symbols per second. That means it shifts a constant carrier's
> > > phase between 8 different polar degree positions 2400 times per
> > > second. This raw bit speed is modified by software to get a "data
> > > channel" at various selectable levels from 75 baud to 4800 baud.
> > >
> > > The lower baud rates such as 75 baud, provide more robust comms,
> > > capable of low SNR, and operation in weak signal conditions.
> > > The highest baud rates such as 2400 baud provide faster data
> > > throughput but require a somewhat better quality channel, not
> > > weak signals.
> > >
> > > This -110 "MIL Standard" 8PSK signal is about 3kHz wide.
> > > It has an audio baseband signal approximately 300Hz to 3300Hz
> > > with a center frequency of 1800Hz. Some of the newer ham radios
> > > have adequate passband width for this signal.
> > >
> > > Since most ham radio and commercial SSB transceivers have a more
> > > narrow passband (~2.5kHz), at least 2 modified non-standard
> > > versions of the -110 PSK signal were independently developed
> > > (MARS-ALE and RFSM2400) to fit within the narrower SSB passband
> > > of ham transceivers.
> > >
> > > The RFSM2400 uses a 6PSK signal at 2000 symbols per second for its
> > > narrow non-MIL-standard mode rather than the 8PSK MIL-standard
> > signal.
> > > It is centered on 1500Hz, and provides an audio baseband signal
> > > that is approximately 300Hz to 2700Hz. It also uses a short burst
> > > of BPSK signal for sync/control.
> > >
> > > Why Multi-Phase PSK?
> > > Phase detection is inherently faster than tone frequency detection
> > > such as used with FSK or MFSK signals. In the present state of the
> > art
> > > for Frequency Shift Keying demodulation, the tone is present for
> > > several cycles to be detected reliably at audio baseband, so this
> > > makes rapid shifts having fewer cycles less reliable, thus limiting
> > > the data speed.
> > >
> > > Phase detection, on the other hand, is reliably detected within a
> > > a cycle. With a 6-phase (6PSK) signal or 8-phase (8PSK)
> > > signal, a greater number of raw symbol bits provides more throughput
> > > than the more common 2-phase (BPSK) or 4-phase (QPSK) signal.
> > >
> > > How the raw symbols are used, and how they are coded for redundancy
> > > and FEC at the software level, can be balanced for optimization of
> > > robustness and throughput for given conditions.
> > >
> > > Why not OFDM or AM-PSK?
> > > The use of full power "constant amplitude", with 8 phase shift or 6
> > > phase shift also makes the -110 PSK type signals more robust for HF
> > > than signals that depend upon amplitude level, such as OFDM (AM-QPSK
> > > or AM-MPSK).
> > >
> > > Perhaps an OFDM (AM-QPSK) signal with 2-level amplitude shift and 4
> > > position phase shift, could achieve similar robustness to a 6PSK
> > > signal. Such an OFDM signal potentially has more throughput because
> > > the number of raw symbols, and thus number of bits per second,
> > > are higher.
> > >
> > > In weak signal conditions, however, the advantage of PSK
> > > over OFDM (AM-QPSK, AM-BPSK, AM-MPSK) becomes apparent...
> > >
> > > Since this OFDM (AM-QPSK) signal requires amplitude modulation,
> > there
> > > is an inherent sacrifice of raw link margin threshold above noise
> > > for the receiver demodulator to resolve the lower amplitude symbols
> > > that are not at full transmit power. The lower amplitude symbols
> > > of the constellation are resting in the noise, although the higher
> > > amplitude symbols are still above the noise.
> > >
> > > If the OFDM modulation level shift is -6dB for the lower amplitude
> > > symbols, then the OFDM (AM-QPSK) will require a +6dB better SNR
> > > threshold than a PSK signal, all other factors being equal.
> > > However, once that relative threshold as been reached, the OFDM
> > > (AM-QPSK) signal has greater raw throughput potential.
> > >
> > > Comments and discussion are invited.
> > >
> > > Bonnie Crystal
> > > KQ6XA
> > >
> >
> >
> >
> >
> >
> >
>
>
>
>
>
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