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I also mentioned QRS which you conveniently forgot
about. Why would I struggle with 1mW when I am permitted 10Watts
G3KEV
----- Original Message -----
Sent: Saturday, January 23, 2010 8:15
PM
Subject: Re: LF: JT4A simple guide?
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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