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<DIV><FONT color=#000000 size=2 face=Arial>Hi Alberto,</FONT></DIV>
<DIV><FONT color=#000000 size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#000000 size=2 face=Arial>Perhaps I can explain. Both
Mercury and Penelope have 122.88MHz master clocks. These are used to
derive the various signals needed by their respective FPGAs.</FONT></DIV>
<DIV><FONT color=#000000 size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#000000 size=2 face=Arial>Since we generally want to transmit
and receive on the same frequency we can't rely on both of these clocks being on
exactly the same frequency. So we use a 10MHz reference that both these clocks
are locked to. The 10MHz can come from Mercury, Penelope or Atlas ( via
Excalibur perhaps).</FONT></DIV>
<DIV><FONT color=#000000 size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#000000 size=2 face=Arial>If you use a high accuracy external
10MHz reference - say a GPS locked reference, then your Tx and Rx frequencies
also be very accurate. We have reports of folks having an accuracy
of 2 mHz ( 2 milli Hz!).</FONT></DIV>
<DIV><FONT color=#000000 size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#000000 size=2 face=Arial>If you don't select any 10MHz
reference then you may get lucky and find your two 122.88MHz master clocks are
close enough not to be a problem.</FONT></DIV>
<DIV><FONT color=#000000 size=2 face=Arial>So if you have a nice accurate clock
and you remove your 10MHz reference then, as you found, you may only move a few
Hz.</FONT></DIV>
<DIV><FONT color=#000000 size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#000000 size=2 face=Arial>In my shack today it reached 34C - I
can tell you my clock moved a lot more than 2Hz without a 10MHz reference
connected!</FONT></DIV>
<DIV><FONT color=#000000 size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#000000 size=2 face=Arial>73's Phil....VK6APH </FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; 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=hpsdr@lists.openhpsdr.org
href="mailto:hpsdr@lists.openhpsdr.org">HPSDR list</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, December 21, 2009 7:42
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [hpsdr] Disabling 10 MHz
clock on Penelope</DIV>
<DIV><BR></DIV>***** High Performance Software Defined Radio Discussion List
*****<BR><BR>
<P>
<HR>
<P></P>I never understood how it can be possible that if you disable the
Penelope 10 MHz clock <U>and</U> the Mercury 10 MHz clock,<BR>deselecting the
relative bits in the USB stream inbound to the HPSDR, nevertheless reception
continues, <BR>albeit on a frequency a few Hz removed, but still with xtal
stability...<BR><BR>73 Alberto I2PHD<BR>
<P>
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