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<DIV><FONT face=Arial color=#000000 size=2>Hi Alberto, </FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>Let me see if I can shed some light
on what is happening. If you use Mercury and Penelope you need a way to
phase lock the 122.88MHz clocks on each board. There are a number of ways
you can do this:</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>1. Use the 10MHz TCXO on Mercury
</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2>2. Use the 10MHz TCXO on
Penelope</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2>3. Use an external 10MHz reference on
Atlas C16 e.g. Excalibur</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>The TCXO's on Mercury and Penelope
are not intended to be highly accurate - just good enough to lock the two
122.88MHz clocks together. If you would like higher accuracy then use an
external reference. </FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>The 122.88MHz clocks on Mercury and
Penelope are divided down to 80kHz as is the 10MHz reference from Penelope or
Mercury or Atlas. The two 80kHz signals are presented to an OR gate which
is used as a phase detector in a PLL. </FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>So if you select Atlas as your 10MHz
source, and there is no 10MHz signal on it, then the output of the OR gate phase
detector will be a 80kHz square wave. After this passes through the PLL
filter the output is a DC voltage at 3.3/2 volts. This voltage is
fed to the 122.88MHz VCXO which sets it to the mid point of its frequency
range.</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>If you are lucky, and have a good
122.88MHz clock, then this could be very close to 122.88MHz - closer than if you
phase lock it to the relatively low accuracy 10MHz TCXOs. </FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>Hence you may find your frequency
accuracy is actually better with no 10MHz clock on Atlas rather than using the
10MHz TCXO on Mercury/Penelope.</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>If you want higher accuracy then use
an external 10MHz reference. If you use Penelope and Mercury,
and select Atlas as your 10MHz reference, then you MUST have an actual signal on
it or - depending on how good you luck is - you will have a
frequency difference between Tx and Rx. </FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>No mystery - just simple
electronics!</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2>73's Phil...VK6APH</FONT></DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<DIV><FONT face=Arial color=#000000 size=2></FONT> </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=i2phd@weaksignals.com href="mailto:i2phd@weaksignals.com">Alberto
I2PHD</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=n3ick@cox.net
href="mailto:n3ick@cox.net">Keith</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Cc:</B> <A title=hpsdr@lists.openhpsdr.org
href="mailto:hpsdr@lists.openhpsdr.org">hpsdr@lists.openhpsdr.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, June 08, 2009 6:51 PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [hpsdr] 10 MHz clock
source</DIV>
<DIV><BR></DIV>***** High Performance Software Defined Radio Discussion List
*****<BR><BR>
<P>
<HR>
<P></P>Keith wrote:
<BLOCKQUOTE cite=mid:8F8CDABDF42A42BCBE41608BE87BD2BD@radiopc type="cite"><PRE wrap="">Hello Alberto
I noticed the frequency shift when working PSK31 before the latest updates
and was told that on Mercury if I shorted across R37 it would get it much
closer. I tried it and the frequency is very close now 10-15hz. I believe
there is an eco out for the change it has to do with the leading edge of the
clock pulse on the C1 bus of Atlas. Hope this helps
73 de N3ICK
</PRE></BLOCKQUOTE>Hello Keith,<BR><BR> thanks for your answer. Will
have a look at that EC.<BR>But still don't understand where the 10 MHz clock
comes from, when Atlas is selected as source...<BR><BR>73 Alberto
I2PHD<BR><BR>
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