<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000066">
Phil Harman wrote:
<blockquote cite="mid:62089307944E4E28A98C48333687C9C9@phil" type="cite">
<meta content="text/html; charset=iso-8859-1"
http-equiv="Content-Type">
<meta name="GENERATOR" content="MSHTML 8.00.6001.18854">
<style></style>
<div><font color="#000000" face="Arial" size="2">Hi Alberto,</font></div>
<div> </div>
<div><font color="#000000" face="Arial" size="2">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> </div>
<div><font color="#000000" face="Arial" size="2">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. <br>
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> </div>
<div><font color="#000000" face="Arial" size="2">If you use a high
accuracy external 10MHz reference - say a GPS locked reference, then
your Tx and Rx frequencies also be very accurate. <br>
We have reports of folks having an accuracy of 2 mHz ( 2 milli Hz!).</font></div>
<div> </div>
<div><font color="#000000" face="Arial" size="2">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" face="Arial" size="2">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> </div>
<div><font color="#000000" face="Arial" size="2">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> </div>
<div><font color="#000000" face="Arial" size="2">73's Phil....VK6APH </font></div>
</blockquote>
Hi Phil,<br>
<br>
that makes a lot of sense, still I am puzzled, as I don't have any
external reference connected to the Atlas bus, it has only Ozy, Mercury
and Penelope.<br>
So my question still is, when I disable both Mercury and Penelope as
sources of the 10 MHz clock, where does the Atlas bus pick up the clock
that is then<br>
used to receive ? Mind, I haven't used Penelope for transmitting, yet.
I just noticed that, when receiving, I have three possibilities for the
source of that<br>
clock, Mercury, Penelope or none of the two. Each choice corresponds to
a slightly different frequency.... who generates the 10 MHz clock when
neither<br>
of the two cards is selected ??<br>
<br>
73 Alberto I2PHD<br>
<br>
<br>
<br>
</body>
</html>
1261418483.0