[hpsdr] Disabling 10 MHz clock on Penelope

[Phil Harman]

>   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>

Hi Alberto,

OK - I think we are close.  The 122.88MHz reference clock used on Mercury
and Penelope is a VCXO. Without any 10MHz reference to the PLL the control
voltage to the VCXO will be at mid rail i.e.  3.3/2v.  In which case the
VCXO will run at its nominal frequency - 122.88MHz.  Since its a high
performance, low phase noise, crystal oscillator this is fine - the only
issue is, due to the manufacturing tollerances, it may be a little off
frequency.

In your case it sounds like you have a very good VCXO in that your
external 10MHz reference only has to correct for a few Hz frequency error.

If you don't select Penelope or Mercury or Excalibur and you don't have a
10MHz reference connected to Atlas C16 then  this is the situation - the
PLL runs open loop.

73's Phil...VK6APH




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