[hpsdr] Distorted audio

[Chris Smith]

Hi Phil & Jeremy

I eventually found the problem. My rather makeshift connection for power to the Trimble Thunderbold had failed in that the Gnd/0V lead had become disconnected. Having remade the connection all is well and the LEDs on Excalibur are once again cycling red/green slowly. 

Thanks once again for your help. I feel rather embarrassed that the problem was of my own making in taking a short-cut.

Cheers & 73

Chris G4NUX

On 10 Aug 2011, at 08:45, Phil Harman wrote:

> Hi Chris,
> 
> If the TXCO has just drifted off frequency there is an adjustmet screw on
> the lid that you may find will bring it back on frequency.
> 
> 73 Phil....VK6APH
> 
> 
>> ***** High Performance Software Defined Radio Discussion List *****
>> 
>> Hi Jeremy
>> 
>> I was being rather lazy with my language re phase lock. You are correct
>> that the LEDs simply indicate the difference between the external input
>> and the internal oscillator. I had been used to seeing the LEDs change
>> colour very slowly indicating that the internal oscillator was very close
>> in frequency to the external Thunderbolt reference. Now both LEDs appear
>> to be on (actually switching colour at a frequency too high for my eyes to
>> differentiate).
>> 
>> I tried moving the jumper on Excalibur so that the internal oscillator was
>> used but that didn't alter the distortion.
>> 
>> I will try your suggestion of removing Excalibur and configuring PSDR to
>> select 10MHz from Mercury later this morning. If that cures the problem
>> have you any recommendations as to where to start looking on Excalibur?
>> The only common signal path involves U2 and the 3v3 regulator which
>> supplies it. The o/p from the BNC socket at 1V RMS looked clean on an old
>> 'scope but the timebase only goes to 0.5uS per div.
>> 
>> I'll check all the regulators while I'm at it.
>> 
>> Thanks.
>> 
>> 73 Chris G4NUX
>> 
>> On 10 Aug 2011, at 03:17, Jeremy McDermond wrote:
>> 
>>> On Aug 9, 2011, at 11:51 AM, Chris Smith wrote:
>>> 
>>>> ***** High Performance Software Defined Radio Discussion List *****
>>>> 
>>>> Hmmm...  I've just turned on my HPSDR kit for the 1st time in about a
>>>> month and was horrified to hear a very distorted audio output. CW
>>>> signals sound like T4/5 report.
>>>> 
>>>> I haven't yet 'scoped the 13.8V line or the various O/Ps from LPU but
>>>> everything seems to be working except Excalibur has lost phase lock
>>>> with the Trimble Thunderbolt reference and no amount of tweaking the
>>>> trimmer on X1 will pull it back into lock.
>>> 
>>> I had the TCXO go out on my Excalibur causing it not to be able to
>>> correctly lock up.  It caused a persistent warble in the signal because
>>> Mercury was valiantly trying to phase lock to the 10MHz signal.  You
>>> might try taking out Excalibur and using Mercury as your clock source
>>> and see what happens.
>>> 
>>> My understanding is, though, that Excalibur doesn't phase lock your
>>> external clock to the X1 oscillator.  The jumper chooses either one or
>>> the other, processes it into a square wave, and puts it on the Atlas bus
>>> C16.  The LEDs merely indicate the difference between the external input
>>> and the internal oscillator.
>>> 
>>>> Any ideas?
>>>> 
>>>> Chris G4NUX
>>> 
>>> --
>>> Jeremy McDermond (NH6Z)
>>> Xenotropic Systems
>>> mcdermj at xenotropic.com
>>> 
>>> 
>>> 
>>> 
>> 
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> 
> 


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