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PA2AGA > HDDIG 17.06.00 20:35l 167 Lines 7095 Bytes #-9440 (0) @ EU
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Sent: 000617/1432Z @:PI8HGL.#ZH1.NLD.EU #:52095 [Den Haag] FBB $:HD_2000_166C
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Sat, 17 Jun 00 14:34:36 MET
Message-Id: <hd_2000_166C>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
>the dxcluster.
I don't think Rob is talking about the gamers. They generally aren't
interested in *weak* signals anyway. He is right that the Hell modes
will work when the auroral flutter makes a hash of PSK31, or when
the intense multipath on short skip 80m does likewise. On a pure
gaussian channel, they're about a wash. But we rarely see a pure
gaussian channel on HF.
>> But I still prefer Pactor 1 with its ERROR FREE copy. (I even prefer AMTOR
>> over PSK31 with its almost error free copy)
>>
>> Rob
>
>Rob, you're not making any sense. PSK31 is a minimum bandwidth mode
>(more power per BW/Hz). AMTOR and PACTOR are not even in the same
>class. They are ultra-wide shift FSK (in comparison).
And that's often a good thing when faced with skywave multipath. A wider
shift would be even better, which is why the best designed HF protocols
use wide shifts. It offers frequency diversity when the proper sort of
demodulator
is used. That can sharply improve performance in the presence of skywave
multipath. PSK31's very narrow shift offers virtually no frequency diversity
gain.
The thing about HF signals is not that they're very weak, hell you can hear
most of them with your ears, and a matched filter is just as effective for
separating a wide shift signal from the noise as it is for separating a narrow
signal (it is the baud that ultimately determines the Eb/No you'll have).
The extreme example of that is spread spectrum.
The key thing about HF signals is skywave multipath. To get good solid
copy, you need a mode that's very resistant to it (or lots of brute force
power to punch through regardless). Three ways to do that are wide shift,
which gives frequency diversity, multiple transmission symbols per bit,
which makes the signal more immune to multipath and interference, and
a strong FEC, which recovers damaged symbols.
PSK31 is a nice RTTY replacement for casual chatting between amateurs,
but it isn't the best choice for getting the message through under harsh
conditions. As Rob notes, under some conditions AMTOR or a Hell mode
are better (but wider multitone methods employing strong FEC are better
still, see Clover II, PACTOR II, or especially MT63 for current amateur
examples, or check out the work done by KA9Q and N4HY for less well
known but even better methods).
The big advantages of PSK31 are that it is very cheap to implement (free
for most of us), and that the programs which do it are very user friendly.
Those are the primary reasons it has become popular. The fact that it
also coexists well with other modes has allowed it to gain ready acceptance
by the users of other modes. That's a factor that can't be ignored on HF
with the current mix of modes.
PSK31 is becoming the CW equivalent for the new age. It is not the best
when a message has got to get through correctly under harsh conditions,
but it is adequate for lots of things that amateurs want to do.
Gary
Gary Coffman KE4ZV | You make it |mail to ke4zv@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
------------------------------
Date: Wed, 14 Jun 2000 14:34:27 -0400
From: "Rob" <Pse@NoEmail.Com>
Subject: PacComm Pactor I Controller. Opinions?
Hi Gary,
Many thanks for your comments.
I agree that PSK31 is terrible when there is any polar flutter. At this
QTH, I have NOT been able to make any QSO's with JAPAN on PSK31 even with
strong signals due to the adverse effects of polar flutter.
But I can make QSO's with Japan on AMTOR, PACTOR or Hell despite the
presence of polar flutter. I am sure the wider shift is a factor. I have
noticed that when using RTTY, AMTOR or PACTOR copy can be significantly
improved under poor conditions when using a shift wider than the typical 170
Hz or 200 Hz shift.
I have used 500 Hz shift AMTOR and PACTOR on the less crowded H.F. bands
with great results. Most modems can operate wide shift AMTOR and PACTOR but
it is rarely used. Wide Shift RTTY also works well under poor HF
conditions. I still remember the days when 850 Hz RTTY was popular.
MT63 is also a great mode but the default mode uses 1000 Hz which partly
explains its good performance in dealing with polar flutter. But I suspect
that MT63's use of strong FEC is another big factor.
But most HAM's seem to forget about the Feld Hell modes including all the
great NEW designer Feld Hell modes like PSK Hell. In my view the Hell modes
are great for keyboard QSO's. Some HAM's call the Hell modes FUZZY modes
since each character is sent as an image. Under really bad conditions, your
brain makes the final decision on what character was actually sent. As
every HAM knows, the human brain is better at copying weak CW signals than
any computer modem. Hell is no different.
Since you are actually sending images in Hell, you can also send small icons
such as an icon for a rig etc. Lots of fun.
I have also found that the new designer Hell mode -- PSKHell -- is more
sensitive than PSK31. In addition, polar flutter does not affect PSKHell as
much as PSK31.
There is great FREE windows software by IZ8BLY for Feld Hell including the
designer Hell modes like PSKHell. For more information see
www.qsl.net/zl1bpu
There only has been ONE article written in QST on Hell. Compare that with
the multiple articles published in QST on PSK31. Unfortunately, the article
on Hell was submitted to QST before the development of PSKHell. Too bad. I
wish more Hams knew about PSKHell.
73's
Rob
"Gary Coffman" <ke4zv@bellsouth.net> wrote in message
news:ddafkssh4la1h9qs4d71l9b1ov9qj5849v@4ax.com...
> On Wed, 14 Jun 2000 06:56:36 -0500, "Steve Sampson"
<ssampson@usa-site.net> wrote:
> >"Rob" <Pse@NoEmail.Com> wrote
> >> Yes, more Hams seem to be using PSK31 (or even PSKHELL) modes for
keyboard
> >> to keyboard QSO's. I suspect that since you can get on PSK31 or
PSKHELL by
> >> simply using your computer with a sound card and FREE software may be
the
> >> reason.
> >
> >Gee, do you think so? I think the second reason, is that you can crank
down
> >the power (5 watts instead of 50).
> >
> >>(By the way, PSKHELL is a better mode than PSK31 for really weak DX
> >> QSO's!).
> >
> >Give me a break! Do you make this stuff up as you go along? A DX'er
> >wouldn't be caught dead without a digital voice player and computer
> >generated CW. "CQ DX, CQ CONTEST", "YOU'RE 59". Three
> >buttons, that's all you need. DX'ers never heard of packet, other than
> >the dxcluster.
>
> I don't think Rob is talking about the gamers. They generally aren't
> interested in *weak* signals anyway. He is right that the Hell modes
> will work when the auroral flutter makes a hash of PSK31, or when
> the intense multipath on short skip 80m does likewise. On a pure
> gaussian channel, they're about a wash. But we rarely see a pure
> gaussian channel on HF.
To be continued in digest: hd_2000_166D
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