[hpsdr] Angelia and Hermes External Clock problem

[Helmut, DC6NY]

Hi Stijn,

no disagreement! I also don't know why the designer saved such a hex
inverter or similar on Hermes/Angelia. Most other hardware details and
components are a 100% copy of Mercury, Penny and Metis. On all of these
cards the same 'simple' TCXO is used to feed the FPGA with a clipped sine
signal. May be that's an issue in frequency critical applications. In that
case Mike, KF4BQ, found an appropriate solution. It seems also possible to
feed an adjusted external square wave signal directly via the SMA jack and a
short piece of thin coax to J20.

73, Helmut, DC6NY

 
-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Stijn Nestra
Gesendet: Dienstag, 20. August 2013 15:38
An: hpsdr at lists.openhpsdr.org
Betreff: Re: [hpsdr] Angelia and Hermes External Clock problem

***** High Performance Software Defined Radio Discussion List *****

Hello Helmut ea.

Indeed Atlas is a solid platform in this regards and Hermes has some parts
loaned from this system. But in the external clock circuitry some parts have
been omitted. Excalibur in the Atlas system contains except the clock shaper
also a 74ac04 buffer. This takes care of the fast rice-times that we seem to
be missing on Hermes. The second thing this
74ac04 does is: it protects the fpga input a bit against overvoltage since
the 74ac04 is powered by 3.3v and not 5v.

Sincerely,

Stijn PE1RKS

Op 20-08-13 12:25, Helmut, DC6NY schreef:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Mike,
>
> you are absolutely right, an additional 3V Schmitt-trigger would be 
> fine to provide a clean square pulse.  On the other hand you know that 
> HERMES and of course ANGELIA are an integration circuitry of the Atlas 
> based cards with solid experience  of the performance.  The small 
> on-board TCXO always exhibits a short time stability of +/- 2 Hz 
> providing a simple clipped sine pulse.
> I’m not responsible for the design, but I never saw a big issue in the 
> current version of Hermes in daily use due to dropouts.
> BTW on my Atlas based configuration I using a external homebrew 10 MHz 
> source (not identical with Excalibur), but also prophylactically 
> equipped with a 3V Schmitt-trigger, hi.
>
> 73, Helmut, DC6NY
>
> -----Ursprüngliche Nachricht-----
> Von: hpsdr-bounces at lists.openhpsdr.org 
> [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Mike Collins
> Gesendet: Montag, 19. August 2013 21:26
> An: hpsdr at lists.openhpsdr.org
> Betreff: Re: [hpsdr] Angelia and Hermes External Clock problem
>
> ***** High Performance Software Defined Radio Discussion List *****
>
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