[hpsdr] Penelope changes for Excalibur?

[Riho, ES7AAZ]

Hi  Bruce , N1RX

Is there any improvement of 10MHz harmonics on freq. 20, 30, 40, 50MHz  
when  Penelope 10MHz is disabled ?

73's,
Riho, ES7AAZ
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>
> n3evl wrote:
>   
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> I'm almost finished construction of Excalibur and will be ready to try 
>> it out soon.
>>
>> I seem to recall some discussion relating to disabling the on-board 
>> 10MHz osc on Penelope.
>>
>> Have I remembered this correctly and is this considered an essential 
>> hardware change?
>>
>> Is it only Penelope that is affected (I don't remember seeing any 
>> similar discussion for Mercury)?
>>
>> I plan (initially) on using Excalibur's on board TXCO but will likely 
>> add an external ref later.
>>
>> Can any of the Penelope/Excalibur resident experts clarify the need 
>> for this possible change and provide details (picture would be nice) 
>> of exactly what/where/how to achieve this.
>>
>> Thanks, and Happy New Year to all on the HPSDR list.
>>
>> Pete, N3EVL
>>     
>
>
> Hi Pete. I was the one who posted some info about disabling the 10 MHz clock
> on Penelope. As Graham stated, Mercury had a jumper included on the board to
> cut power it's own 10MHz clock. This was presumably designed in so one could
> disable the onboard clock if one was using Penelope as the 10 MHz source.
> This jumper was not included in the design of Penelope. 
>
> Once I added Excalibur to my system, I added a jumper to my Penelope for
> this purpose. It is a simple mod, and in my opinion does not represent
> "cutting up" my board. I have posted two pictures showing the mod here:
>
> http://home.myfairpoint.net/vze1t5sc/Penelope10MHz_detail.jpg
>
> http://home.myfairpoint.net/vze1t5sc/Penelope10MHz_detail2.jpg
>
> You can see the new 2-pin jumper just to the right of the 10MHz clock chip
> (U2). It is located just below the 3V3 silkscreen at the top of the board.
> It is a standard, 0.1 inch spacing 2 pin right angle header. First the trace
> is cut to the upper right pin (3.3v line) of U2. Then the header is
> installed across the gap. This allows the oscillator to be re-powered, if
> ever desired.
>
> As Phil said, it is not mandatory to do this. You could just leave the clock
> running. However doing so leaves the another RF source running in the
> system, with the potential for mixing products producing birdies in the
> receiver. As this is High Performance SDR, I decided to do this simple mod.
>
> As a side note, I use an external reference with Excalibur. With nothing
> connected to the antenna on Mercury ,I can tune the receiver to 10 MHz and
> see a nice peak from the external reference clock. If I tune to 9.999.4 MHz
> USB, I can produce a nice 600 Hz note in the audio out. I have used this
> note to calibrate the soundcard clock on my computer, using Spectrum Lab.
> This is done to obtain the most accurate results on frequency measuring
> tests. In the zoomed spectrum of the audio, I can clearly see a second peak
> caused by the onboard TXCO on Excalibur. I may eventually modify my
> Excalibur board to disable the onboard TXCO whenever an external clock is
> detected. At some point, as an experiment I may reenable the clock on
> Penelope, and see if I can discern a signal from that as well.
>
> Again, diasbling the clock on Peenelope is not needed for most applications.
> But for some, and for those that have not been dreamed up yet, it may be
> beneficial.
>
> 73,
> Bruce Beford, N1RX
>
>
>
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