From: Rik Strobbe <rik.strobbe@kuleuven.be>
To: "rsgb-lf-group@groups.io" <rsgb-lf-group@groups.io>
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Thread-Topic: [rsgb-lf-group] FW: JT9-5 Drift
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Date: Mon, 7 Jan 2019 13:34:15 +0000
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Hello Andy,


the drift is given as Hz/min, so for JT9-5 the drift can be as high as 1Hz =
over the (almost) 5 minute TX cycle.

The decoder must somehow be able to correct the drift within certain limits=
.


73, Rik  ON7YD - OR7T



________________________________
Van: rsgb-lf-group@groups.io <rsgb-lf-group@groups.io> namens Andy TALBOT <=
andy.g4jnt@gmail.com>
Verzonden: maandag 7 januari 2019 14:13
Aan: rsgb-lf-group@groups.io
CC: rsgb_lf_group@blacksheep.org
Onderwerp: Re: [rsgb-lf-group] FW: JT9-5 Drift

The JT9-5 tone spacing is 0.29Hz, so those drift figures correspond roughly=
 to a bit less than one complete tone spacing in the transmission period.  =
Which makes intuitive sense.  The error correction allows it to "lose" the =
few symbols at the end where it has drifted too far, while those at the sta=
rt are near enough to work normally.

(Pure speculation) The soft decision process in the decoder algorithm will =
base its metric on how far the received signal is away from where it ought =
to be, so a tone  that has drifted into an adjacent bin may still have a qu=
ite strong weighting applied.

BTW Rik, you still appear to be copying these posts to the now-dead Yahoo G=
roup

Andy
www.g4jnt.com<http://www.g4jnt.com>



On Sun, 6 Jan 2019 at 10:48, Rik Strobbe <rik.strobbe@kuleuven.be<mailto:ri=
k.strobbe@kuleuven.be>> wrote:

Dear all,


Roger, VK4YB, asked me about JT9-5 frequency stability requirement.

As this might be interesting for others too, my answer below.


73 & HNY


Rik  ON7YD - OR7T


________________________________
Van: Rik Strobbe
Verzonden: zondag 6 januari 2019 11:43
Aan: Roger Crofts
Onderwerp: Re: JT9-5 Drift


Hello Roger,


as JT9-2 and JT9-5 signals are resampled to JT9-1 to be decoded by WSJT dec=
oder engine it all depends on the drift tolerance of that decoder.

For JT9-2 the frequency stability must be 2.222 times better than for JT9-1=
.

For JT9-5 it must even be 5.926 be better.

As I couldn't find any information about the required JT9-1 stability I did=
 some brief tests with JT9-5:

- At -5 dB level a drift up to 0.35 Hz/min seems acceptable.

- At -15 dB level it is 0.26 Hz/min.

- At -25 dB level it is 0.24 Hz/min

- At -30 dB level it is 0.22 Hz/min

- At -34 dB level (more or less the JT95 limit) it is 0.20 Hz/min

But as said this was just a brief test, these numbers should be handled wit=
h some caution.

Also keep in mind that this numbers represent the combined TX and RX drift =
(according to Murphy TX and RX drift will always be opposite).

If using a transverter the TX drift is the combined drift of the driver TX =
and the transverter.

Furthermore I assumed that the drift was linear over time, for frequency ju=
mps it might be different.

Another frequency instability source will be the ionosphere, but there is l=
ittle we can do about that (but the more stable TX and RX the more room for=
 ionospheric instabilities).

Based on the above I would suggest to aim for a LO stability of no worse th=
an 0.1 Hz/min, 0.05 Hz/min would be even better for weak signal DX (and tha=
t is what JT9-5 is all about).


Tests over the past weeks have shown that JT9-5 works very well for 136 kHz=
 DX (N1BUG was copied by numberous EU stations).

On 472 kHz K3MF has been reported in Europe (as far as I know by G0LUJ and =
myself).


73, Rik  ON7YD - OR7T

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1">
<style type=3D"text/css" style=3D"display:none"><!-- p { margin-top: 0px; m=
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<p>Hello Andy,<br>
</p>
<p><br>
</p>
<p>the drift is given as Hz/min, so for JT9-5 the drift can be as high as 1=
Hz over the (almost) 5 minute TX cycle.<br>
</p>
<p>The decoder must&nbsp;somehow be able to correct the drift within certai=
n limits.<br>
</p>
<p><br>
</p>
<p>73, Rik&nbsp; ON7YD - OR7T<br>
</p>
<p><br>
</p>
<p><br>
</p>
<div style=3D"color: rgb(33, 33, 33);">
<hr tabindex=3D"-1" style=3D"display:inline-block; width:98%">
<div id=3D"divRplyFwdMsg" dir=3D"ltr"><font face=3D"Calibri, sans-serif" co=
lor=3D"#000000" style=3D"font-size:11pt"><b>Van:</b> rsgb-lf-group@groups.i=
o &lt;rsgb-lf-group@groups.io&gt; namens Andy TALBOT &lt;andy.g4jnt@gmail.c=
om&gt;<br>
<b>Verzonden:</b> maandag 7 januari 2019 14:13<br>
<b>Aan:</b> rsgb-lf-group@groups.io<br>
<b>CC:</b> rsgb_lf_group@blacksheep.org<br>
<b>Onderwerp:</b> Re: [rsgb-lf-group] FW: JT9-5 Drift</font>
<div>&nbsp;</div>
</div>
<div>
<div dir=3D"ltr">
<div dir=3D"ltr">
<div class=3D"gmail_default" style=3D"font-family:tahoma,sans-serif; font-s=
ize:small">
The JT9-5 tone spacing is 0.29Hz, so those drift figures correspond roughly=
 to a bit less than one complete tone spacing in the transmission period.&n=
bsp; Which makes intuitive sense.&nbsp; The error correction allows it to &=
quot;lose&quot; the few symbols at the end where it
 has drifted too far, while those at the start are near enough to work norm=
ally.</div>
<div class=3D"gmail_default" style=3D"font-family:tahoma,sans-serif; font-s=
ize:small">
<br>
</div>
<div class=3D"gmail_default" style=3D"font-family:tahoma,sans-serif; font-s=
ize:small">
(Pure speculation) The soft decision process in the decoder algorithm will =
base its metric on how far the received signal is away from where it ought =
to be, so a tone&nbsp; that has drifted into an adjacent bin may still have=
 a quite strong weighting applied.&nbsp;<br>
</div>
<div class=3D"gmail_default" style=3D"font-family:tahoma,sans-serif; font-s=
ize:small">
<br>
</div>
<div class=3D"gmail_default" style=3D"font-family:tahoma,sans-serif; font-s=
ize:small">
BTW Rik, you still appear to be copying these posts to the now-dead Yahoo G=
roup</div>
<div class=3D"gmail_default" style=3D"font-family:tahoma,sans-serif; font-s=
ize:small">
<br>
</div>
<div class=3D"gmail_default" style=3D"font-family:tahoma,sans-serif; font-s=
ize:small">
<span class=3D"gmail_default"></span><span style=3D"font-family:Arial,Helve=
tica,sans-serif">Andy</span><br>
</div>
<div>
<div dir=3D"ltr" class=3D"gmail_signature">
<div dir=3D"ltr">
<div dir=3D"ltr">
<div dir=3D"ltr">
<div dir=3D"ltr">
<div dir=3D"ltr">
<div><span style=3D"font-size:12.8px"><a href=3D"http://www.g4jnt.com" targ=
et=3D"_blank">www.g4jnt.com</a></span><br>
</div>
<div><br>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<br>
</div>
<br>
<div class=3D"gmail_quote">
<div dir=3D"ltr">On Sun, 6 Jan 2019 at 10:48, Rik Strobbe &lt;<a href=3D"ma=
ilto:rik.strobbe@kuleuven.be">rik.strobbe@kuleuven.be</a>&gt; wrote:<br>
</div>
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex; border=
-left:1px solid rgb(204,204,204); padding-left:1ex">
<div dir=3D"ltr" style=3D"font-size:10pt; color:rgb(0,0,0); background-colo=
r:rgb(255,255,255); font-family:Tahoma,Geneva,sans-serif">
<p>Dear all,<br>
</p>
<p><br>
</p>
<p>Roger, VK4YB, asked me about JT9-5 frequency stability requirement.<br>
</p>
<p>As this might be interesting for others too, my answer below.<br>
</p>
<p><br>
</p>
<p>73 &amp; HNY<br>
</p>
<p><br>
</p>
<p>Rik&nbsp; ON7YD - OR7T<br>
</p>
<p><br>
</p>
<div dir=3D"ltr" style=3D"font-size:10pt; color:rgb(0,0,0); background-colo=
r:rgb(255,255,255); font-family:Tahoma,Geneva,sans-serif">
<hr style=3D"display:inline-block; width:98%">
<div id=3D"gmail-m_-3596027944874736319divRplyFwdMsg" dir=3D"ltr"><font fac=
e=3D"Calibri, sans-serif" color=3D"#000000" style=3D"font-size:11pt"><b>Van=
:</b> Rik Strobbe<br>
<b>Verzonden:</b> zondag 6 januari 2019 11:43<br>
<b>Aan:</b> Roger Crofts<br>
<b>Onderwerp:</b> Re: JT9-5 Drift</font>
<div>&nbsp;</div>
</div>
<div>
<p>Hello Roger,<br>
</p>
<p><br>
</p>
<p>as JT9-2 and JT9-5 signals are resampled to JT9-1 to be decoded by WSJT =
decoder&nbsp;engine it all depends on the drift tolerance of that decoder.<=
br>
</p>
<p>For JT9-2 the frequency stability must be 2.222 times better than for JT=
9-1.<br>
</p>
<p>For JT9-5 it must even be 5.926 be better.<br>
</p>
<p>As I couldn't find any information about the required&nbsp;JT9-1 stabili=
ty I did some brief&nbsp;tests with JT9-5:<br>
</p>
<p>- At -5&nbsp;dB level a drift up to 0.35&nbsp;Hz/min seems&nbsp;acceptab=
le.<br>
</p>
<p>- At -15&nbsp;dB level it is 0.26 Hz/min.<br>
</p>
<p>- At -25 dB level it is 0.24&nbsp;Hz/min<br>
</p>
<p>- At -30&nbsp;dB level it is 0.22 Hz/min<br>
</p>
<p>- At -34 dB level (more or less the JT95 limit) it is 0.20 Hz/min<br>
</p>
<p>But as said this was just a brief test, these numbers should be handled =
with some caution.<br>
</p>
<p>Also keep in mind that this numbers represent the combined TX and RX dri=
ft (according to Murphy TX and RX drift&nbsp;will always be opposite).<br>
</p>
<p>If using a transverter the TX drift is the combined drift of the driver =
TX and the transverter.<br>
</p>
<p>Furthermore I assumed that the drift was linear over time, for frequency=
 jumps it might be different.<br>
</p>
<p>Another frequency instability source will be the ionosphere, but there i=
s little we can do about that (but the more stable TX and RX the more room =
for ionospheric instabilities).<br>
</p>
<p>Based on the above I would suggest to aim for a LO stability of no worse=
 than 0.1 Hz/min, 0.05 Hz/min would be even better for weak signal DX (and =
that is what JT9-5 is all about).<br>
</p>
<p><br>
</p>
<p>Tests over the past weeks have shown that JT9-5 works very well for 136&=
nbsp;kHz DX (N1BUG was copied by numberous EU stations).<br>
</p>
<p>On 472 kHz K3MF has&nbsp;been reported in Europe (as far as I know by G0=
LUJ and myself).<br>
</p>
<p><br>
</p>
<p>73, Rik&nbsp; ON7YD - OR7T<br>
</p>
</div>
</div>
</div>
<p></p>
<p></p>
</blockquote>
</div>
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