[Moon-net] Experimental Digital Modes

[Lance Collister]

Joe Taylor wrote:
 > To:      Users of WSJT
 > From:    Joe Taylor, K1JT
 > Subject: Experimental Modes JT2 and JT4
 > Date:    October 11, 2007
 >
 > Thanks to all who have tested the experimental modes JT2 and JT4 in WSJT 5.9.8 
r558 ... and special thanks if you reported your observations to me or on one of 
the relevant reflectors, or sent me representative wave files.  I can report that 
over the past few days QSOs have now been made with both JT2 and JT4 on amateur 
bands and propagation modes ranging from trans-Atlantic nighttime DX on 1.8 MHz to 
144 MHz EME.  In addition, JT4 has been used to send and receive messages on 10 
GHz EME.
 >
 > If you have not sent comments or a report, it's not too late!  Please note that 
some of the most useful wave files are those containing received signals that you 
think "should" have decoded, but did not.  I am interested in reports of all types 
of on-the-air tests, from HF to microwaves.
 >
 > As described in the announcement posted several days ago at 
http://physics.princeton.edu/pulsar/K1JT/JT2_JT4.TXT , the new modes are basically 
functional but do not yet have certain amenities that JT65 users are accustomed 
to.  The new modes show considerable promise, but for a number of reasons they are 
not yet ready for general use:
 >
 > 1. Decoding performance is overly dependent on the average audio level at the 
sound card input, and perhaps other factors.
 >
 > 2. Software AFC should be included, to correct small frequency drifts.
 >
 > 3. Options for message averaging and matched filtering should be included in 
the decoders.
 >
 > These improvements should not be very difficult to make, but my own schedule is 
such that they will probably take at least some weeks to complete.
 >
 >
 > I have not heard much from others about the appearance of JT2 and JT4 signals 
on the SpecJT waterfall, or the perceived operational importance of the narrow 
bandwidths of these modes compared to JT65.  Some relevant facts are these:
 >
 > 1. JT65B, the dominant mode for 144 MHz EME, has bandwidth B=355 Hz.  JT65A, 
mostly used on HF and 50 MHz, had B=177 Hz.  These modes have a narrow "sync tone" 
only 2.7 Hz wide, which is easy to recognize on a waterfall display.
 >
 > 2. JT2 has bandwidth B=8.75 Hz and JT4A B=17.5 Hz.  In these modes sync 
information is embedded in the data stream. Waterfall traces of JT2 and JT4 
signals are therefore much narrower than the full extent of JT65 signals, but 
appear "fuzzy" compared to the JT65 sync tone.
 >
 > 3. Many JT2 or JT4A signals can fit into the bandpass of a standard SSB 
transceiver without interfering.  This means that random digital EME operation 
could become easy if, for example, JT2 activity were concentrated in a relatively 
small (5 or 10 kHz?) portion of each band.  It would then be possible for WSJT to 
acquire many of the advantages of the MAP65 software, which at present are 
available only to those with wide-band receiving systems like Linrad.
 >
 > 4. The probability for collisions between JT65 signals or between a JT65 signal 
and a birdie is much larger than that for the much narrower JT2 or JT4A signals. 
On the other hand, the JT65 decoder is relatively mature and has been made 
remarkably immune to QRM.  The performance of JT2 and JT4 in comparable situations 
is not yet known.
 >
 > Community input on these matters is needed!  Assuming that the present 
deficiencies of JT2/JT4 can be corrected, so that S/N performance is essentially 
equal to that of JT65, do you consider the narrow bandwidth of JT2/JT4 to be a 
significant advantage?  Or should we forget about JT2/JT4 (at least on bands where 
JT65 is now widely used), and stick with JT65?  Please share your views on these 
and any other questions you think relevant.
 >
 >       -- 73, Joe, K1JT
 >


Hello Joe,

I have not had the opportunity to try JT4A yet (the only reason being
that I am still in the hospital), but I am very excited about the
possibility that it presents for 6m EME.  I look forward to trying it at home on 
6m EME after the EME contest this weekend is over ;-)

The reasons I am so excited about it for 6m EME include the following:

1) Many locations outside Region 2 are subject to intense interference
from "channel 1" TV transmitters, which tend to create spurious
"birdies" spaced about 50 Hz apart.  The fact that JT4A could fit
between such "birdies" could afford great new possibilities for weak
signal work at such locations.

2) Already on DXpeditions it has been demonstrated that there have been QRM 
problems with stations calling on the same exact frequencies as sked stations, 
without regard for keeping a couple hundred Hz spacing.  This should really help 
solve the QRM problem ;-)   Sure, we have the bandwidth up on 6m to accommodate 
more QSO's without QRM, but when people just jump on the same frequency and start 
calling the DX station, it is still a major problem for the DX station to separate 
the stations...the narrower bandwidth should help reduce the possibility of such 
QRM.  I am sure it also will be more popular on the HF bands for similar reasons.

One suggestion I have (from only downloading the software and turning it on with 
out any rig attached):  Please seriously consider making an option for SpecJT to 
look at a narrower bandwidth.  It will be much easier to spot the weaker tones and 
to choose among them if the waterfall display can be made much narrower.

So, in answer to your request for input, please do NOT give up on the new modes! 
Many thanks for your continued dedication to moving weak signal communications 
forward :-)     VY 73, Lance

-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728   URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11, 6m DXCC #815


-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728   URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11, 6m DXCC #815