Mal,
There will be times when this may be true, but modes like WSPR and, I expect, JT4A will get through when signals are extremely weak when CW simply would not.
Here's an idea: why not turning your ERP down to 1mW for a few weeks and see how you get on?
73s
Roger G3XBM
On 23 January 2010 19:32, mal hamilton <[email protected]> wrote:
Obviously not reading recent postings about no
decodes from others although the signals are visible, like I said
these signals are not onljy visible with me but audible so why complicate
matters, just send qrs or cw in the first place.
Some one even mentioned DUMMIES, there are a lot of
these about. Dummies alias Appliance operators
The word is ill-informedtry
g3kev
----- Original Message -----
Sent: Saturday, January 23, 2010 7:17
PM
Subject: Re: LF: JT4A simple guide?
Mal informed.
On 23 January 2010 18:52, mal hamilton <[email protected]>
wrote:
I still see these data signals as a waste of
time since had the carrier been keyed I could read them 100% without having
to wait for the right circumstance to get a decode, no need for level 2
demodulation.
There are several traces now visible but only
an odd decode!!!!!!!!!!!!!!! Try a QRS or CW QSO if you need
an immdediate report. These signals are audible with me.
g3kev
-----
Original Message -----
Sent:
Saturday, January 23, 2010 4:52 PM
Subject:
Re: LF: JT4A simple guide?
Ok, fully understand Andy. Jim G7NKS is sending JT4A
but I'm not getting any decodes yet. Roger G3XBM
On 23 January 2010 16:38, Andy Talbot <[email protected]> wrote:
After posting that, I realised the JT4 PIC/DDS beacon code is
designed for 100% duty cycle operation, viz JT4, CW + carrier, which is
a bit antisocial (certainly the wide bandwidth CW bit). And more
importantly, as my PA is a low efficiency clas AB linear one - enough
said...
To adapt for low duty cycle would need the PIC code changing, so
will put the idea on hold unles there is a real demand. For
a beacon, WSPR has more to offer anyway.
Incidently, WSPR and JT4 are the same mode anyway, albeit with a
bandwidth change from 1.46 to 4.375Hz with a resulting 4.75dB
reduction in S/N. The coding and demodulation are all the same, so
this bandwidth difference should be
directly detectable between the two modes. The differing
message contents wont affect the efficiency, its the added error
correction , sync and modulation that matters - and they use the
same algorithm.
On 23 January 2010 14:43, Roger Lapthorn <[email protected]> wrote:
Thanks
for this help Andy.
I'd not like to derive others of your
valuable 500kHz WSPR beacon, but could you beacon in JT4A at certain
pre-arranged times or days perhaps? If JT4A looks like offering the
possibility of really weak signal QSOs to people like me running
flea-power then I'd like to explore the mode some more and having a
reliable signal to test with initially would be useful. I am sure
there will be others who would value this too.
73s
Roger
G3XBM
On 23 January 2010 14:26, Andy Talbot <[email protected]> wrote:
AFAIK The is no 'simple guide' JT4x was never
originally going to be one of Joe's supported modes, although after
our extensive use on uWaves it certainly is
now. JT65x was the more popular and documented code,
being heavily used for EME on 144 / 432 / 1296MHz,
with JT4x just one of those included in the WSJT suite to 'try
out' If you download and read the WSJT users guide
and other supporting files, there's all you need to know to get
it going is in there.
Its still debatable as to whether JT4 is better or worse than
JT65x, but at least it does have the options of being available in a
range of bandwidths / tone spacings making it usable from DC to red
light. (Although I think I've only ever come across A, D
and G being used respectively on LF, HF and
uWaves) There's probably only a fraction of a dB
in it and both are, as far as I can ascertain, only a dB or two away
from the Shannon limit. [Which knocks spots off CW or any
fuzzy mode, as well as straight PSKnn without error
correction]. Wolf has a similar signalling efficiency,
but unfortunately is wider, needs a linear TX to avoid being too
wide and seems less user friendly.
A year or so ago we (the microwave community) wanted something
for use on 1.3GHz and up to 10GHz or beyond. JT4G,
the widest spaced varient of them looked
suitable. After some prompting, Joe was persuaded
not to abandon that mode, and in fact he modified
the code to enhance the decoder routine so the wide spaced
version would be decoded with the same S/N as
JT4A. We discovered just how good the mode was,
even under severe rainscatter conditions where each tone was spread
out to 200Hz bandwidth (tone spacing in JT4G is 315Hz for 1kH zwide
overall, so this rain scattered signal still had discrete tone
energy).
There are now two microwave beacons that transmit JT4G
waveforms, the 10 and 2.3GHz ones in Dorset GB3SCX
and GB3SCS www.scrbg.org and now GB3CSB on
1.3GHz from central Scotland http://www.rayjames.biz/gm4cxm/id14.html
Other will follow before long as it is quite an easy mode to
generate from a simple PIC keyer provided accurate timing
information is available to keep it synched.
My beacon engine - the one that currently drives the
503.7/503.85 signals - can give JT4A immediately just by
reprogramming the PIC. Would there be any interest,
bearing in mind both the WSPR and "5MHz type" waveforms
will be lost for the duration?
Andy www.g4jnt.comThis email has been scanned
for damaging side-effects by the health and safety police, is
guaranteed to contain no substances hazardous to health, but may
contribute to dissolving the nether and polar
regions
On 23 January 2010 13:48, Roger Lapthorn
<[email protected]> wrote:
Having
looked on the WSJT website there is little (no?) reference
to JT4A in the help files. I assume it is similar to modes like
JT6M which I have managed to receive in the past on 50MHz but
never tried TXing.
Can someone point me in the direction of
a "JT4A for Dummies" guide, or something similar that I
might understand, please?
73s
Roger G3XBM
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