[hpsdr] Resistor value to be changed: R141 of Hermes

[John Ackermann N8UR]

Hi Phil -- can you clarify whether the TAPR-built units have that change?

Thanks!

John

On Feb 24, 2013, at 3:59 AM, "Phil Harman" <phil at pharman.org> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi Tokio,
>  
> Thanks for your comments.  Later versions of the Hermes board did change R141 from 100 ohms to 51 ohms in order to operate more reliably using an external 10 MHz reference. 
>  
> 73 Phil....VK6APH
>  
> From: Tokio Endo
> Sent: Sunday, February 24, 2013 4:54 PM
> To: hpsdr at openhpsdr.org
> Subject: [hpsdr] Resistor value to be changed: R141 of Hermes
>  
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi All,
>  
> I use Hermes by using External 10MHz clock.
> Recently I noticed receiving CW tonality abruptly changed in a very very short period. It's very subtle.
>  
> Then I hooked a probe of an oscilloscoe on JP20 to see the shapes of the clock, when External or Internal.
> The differecne between the both is quite apparent, the output level of two transistor's wave shapping circuit for External clock is low.
>  
> By sharing this phenomenon with Phil, VK6APH, I changed the value of R141 from original 100 ohms to 51 ohms.
> The result is OK, the level is almost same as External clock's one.
>  
> According to the schematics of Hermes as well as BOM, R141 is 100 ohms, but in my case it doesn't work properly.
>  
> If you use External clock, check the value of R141 and see the clock shape of JP20 at JP20 if an oscilloscope is available.
>  
> If there is a difference compared with Internal clock shape, I recommend you to change the value of R141 to 51 ohms.
>  
> 73,
> Tokio Endo
> JA1CCA
>  
>  
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