Hello Steve,
I believe that the FDK/Wanjina system is an excellent tool for propagation
tests, where the only goal is to have an identication of a signal.
The main disadvantage I see is the need of a linear TX, but maybe this
could be solved by transmitting the 2 tones sequential. If the tones are
send sequential they get the double of the power but only during half the
time, so SNR will be the same.
But my primary interest goes to a mode that will allow us to have a proper
2-way QSO within a timeframe of 60-90 minutes.
Assuming that we set the same requirements to have a valid 2-way QSO as for
meteor-scatter or EME than we would need :
1. exchange of callsigns (official calls, no pseudo-calls)
2. exchange of some kind of report (T-M-O)
3. some kind of 'end of QSO' confirmation ('SK')
You are right when you state that FDK/Wanjina does not need absolute
frequency calibration, since each character already carries the reference.
If one would send the tones sequential it would mean that a reference tone
is sent, followed by a second tone with a shift unique for each character.
This is the advantage but at the same time the weakness of FDK, because it
means that you need about 40 different shifts what might become very
difficult to decode by eye and also requires a relative large bandwidth
compared to the proposed 7-tone system.
Regarding SQUID : it sounds rather tempting and might an be interesting
step between simple one-way identication of a beacon and a full 2-way QSO.
But I feel that making a QSO really involves the exchange of regular
callsigns.
73, Rik ON7YD
At 08:04 19/12/01 +1100, you wrote:
G'day All,
Having had some time to think about the 7-tone scheme (I travel 3 hours a
day to work), I must confess to having gone a little cold on the idea.
There are a number of things, but they basically arise from the observation
of conditions which exist at the bleeding edge of long haul efforts. Using
the example of the furthest positive "identification" (carefully
side-stepping the QSO minefield) of Bob Vernall's (ZL2CA) 136kHz
transmissions, the "opening" time available is well below the 60-80 minutes
needed for a QSO. There is simply no time to calibrate on a space as was
suggested. When I consider all the prerequisites and calibration
requirements of the 7-tone scheme, then I look at Wanjina (FDK), where
absolute calibration is not required and "bang", in one 60 second burst of
two simultaneous tone, you get the character, I remember why I have
persisted with my Wanjina system for so long. OK, so I am biassed :-)
However, having successfully had a 2mW EIRP signal decoded over a distance
of 15,000km using Wanjina in the noisy and QRM ridden ISM band
(13.555450Mhz) I think I am entitled to be biassed. The signal was only
known to be be in a range of +/-10Hz, no time synchronisation was used, no
super accurate calibration of the soundcard was required apart from ensuring
that the Wanjina signal was contained somewhere on the Argo screen.
I have a further suggestion to make. I preface this suggestion with Rik's
clarification. The suggestion is not a replacement for the tried and true
methods, but a tool to search out the limits of the medium we are playing
with. For those pioneering efforts (like Bob Vernall's (ZL2CA) crossing of
the Pacific on 136kHz) a super specialised scheme is justified. Here goes.
The first stage of laying the tracks down for others to follow in any
pioneering effort is not to lay down a highway, but simply to establish a
link, however tenuous. Explorers, to establish that they had indeed made
the journey often just left a marker (sometimes just a pile of stones) to
verify the feat.
Most of these pioneering efforts (but not all) have used beacons to
establish the parameters. The first stage of receiving a beacon is to
simply unequivocably identify it. This technique has long been used in
navigation. Lighthouses don't send morse code or a callsign, they send a
unique flash pattern which unambiguously identifies that "beacon".
I suggest that we adopt the same idea. I propose a three "dot" 3-tone
sequential protocol which does not attempt to transmit the alphabet, but
simply to identify the transmitting station plus the TMO reporting system.
Beacons would only transmit the the ID part, those calling for a QSO could
transmit the ID plus a CQ code, those engaged in a QSO could transmit the ID
part plus a TMO part. The sequences must be chosen such that when they are
run end to end (no spaces anywhere) they can be unambiguously identified.
This ambiguity should extend to both beaconing sequences and QSO sequences.
This would mean having to throw away some sequences. This may mean that a
three "dot" 3-tone protocol may not have enough unique sequences to cover
the expected number of participating stations plus TMO and CQ codes and
would have to be extended to either more "dots" or more tones. The
barest minimum should be aimed for to allow wider spacing of tones on a
given resolution Argo screen and to minimise elapsed time for the unique
identification of the station (to take advantage of the short opening times
on the long hauls). The codes should still be much easier to decode by
eye than a 7-tone system.
I haven't had time to do the necessary evaluation to see how many unique and
also sequentially unambiguous codes are available from a 3 "dot" 3-tone
system, but it would need to cover 4-info codes (TMO + CQ) and a limited
number of station IDs (5, 10, 15... ?). I will try and do this on the
weekend or before. I suspect a 3 "dot" 3-tone scheme will not have enough
unique sequences. However, even a 4 "dot" scheme would only take 8 minutes
to send the an ID plus TMO or CQ code using 60 second dots.
I will call this scheme "SQUID" for "Super QUick ID" :-)
Comments ?
Alberto - a question for you. How many lines can you set/reset reliably
from a serial port ? This would set the maximum number of tone
frequencies.
73s Steve Olney (VK2ZTO/AXSO - QF56IK : Lat -33 34 07, Long +150 44 40)
=============================================
HomePage URL: http://www.zeta.org.au/~ollaneg
Containing:-
ULF, ELF, VLF & LF Experimentation
MF 22m Experimentation
InfraSonic Experimentation
Laser Comms DX
=============================================
|
