[RTTY] Information please

[Sean Waite]

There was a discussion on the topband list about JT9 vs JT65. Someone
emailed Joe Taylor and asked him, his response was this:

As you should expect, the correct answer is "it depends".  Depends on
conditions of propagation, QRM, etc.

On an ideal AWGN (additive white gaussian noise) channel JT9 has a 2 dB
advantage over JT65.  But the JT65 code has more redundancy than that in
JT9, and the 2 dB advantage tends to disappear on a fading channel.

JT65 is more robust than JT9 in the presence of QRM (and possibly QRN?).

Overlapping JT65 signals are readily decoded.  Not so much for JT9. Savvy
operators using JT9 often respond to a CQ or tail-end "up" or "down" by 20
Hz or so, thereby avoiding calling on top of another caller.




Hope that helps,
Sean WA1TE

On Fri, May 26, 2017 at 12:50 PM Joe Subich, W4TV <lists at subich.com> wrote:

>
> David,
>
> The JT modes are designed with spreading in mind - their derivation
> was VHF/UHF EME and scatter modes where Doppler is a significant
> issue.
>
> My results have been much like Don's ... with nothing more than [low]
> dipoles and/or an R5 vertical, I have over 150 DXCC entities, WAS on
> 80 - 10 (lacking only AK on 160 and 6 meters) and 130+ grids on 6M
> (of 400+ total).
>
> My only frustration is with a four to five minute QSO none of the
> really rare DX will ever show up on JT65 or JT9 which limits the
> absolute number of entities available on that mode.
>
> 73,
>
>     ... Joe, W4TV
>
>
> On 5/26/2017 10:47 AM, David G3YYD wrote:
> > How well do the JT modes cope with propagation that spreads the signal
> > spectrum? This can be over tens of Hz in the worse case.
> >
> > 73 David G3YYD
> >
> > -----Original Message-----
> > From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of Bill Turner
> > Sent: 26 May 2017 14:11
> > To: RTTY Reflector
> > Subject: Re: [RTTY] Information please
> >
> > ------------ ORIGINAL MESSAGE ------------(may be snipped)
> >
> > On Fri, 26 May 2017 09:20:25 +0100, you wrote:
> >
> >> You could think about using the other data modes. With low power and
> >> poor propagation, PSK can work a lot better than RTTY.
> >> The ultimate move across to the dark side is JT65. I started using JT65
> >> about 10 days ago and have 60+ countries in the log, operating just a
> >> couple of hours a day.
> >> Very low power is all you need, but it's a horrible slow process with
> >> no skill required. My only motivation is to get to 100 DXCC then back to
> > RTTY!
> >> John GW4SKA
> >
> > REPLY:
> >
> > Even better than JT65 is JT9.  A fraction of the bandwidth and according
> to
> > the author, about 2 dB better with weak signals. The protocol is the
> same.
> > Give it a try, you'll like it.
> >
> > 73, Bill W6WRT
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> >
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