[DSP-10] CW transmit has a raspy sound

[Lee Scott - AA1YN]

Hi Bob,

The unlocked 124MHz osc is just basically the free running osc without the 
PLL being programmed. When I connected the DSP-10 to the SA, I hadn't 
downloaded the dsp program yet. Since the signal looked strange with a wide 
band, I thought I'd take a closer look at it prior to booting the dsp. I 
would imagine the control voltage on the varicap diodes was just floating. 
I suppose it could be a bad cap - maybe? I don't know what the freq was but 
I can check it out tomorrow. I'll also try placing a cap in parallel with 
the loop caps to see if that corrects the problem.  If it does, than I'll 
replace that cap. (just a thought).

I kept the osc at 124MHz during the two locked snapshots by adjusting the 
tuning coil L102 thus changing the control voltage on the diodes to see if 
that made any difference. I double checked the loop components just in case 
I made a mistake but they all look fine.  I do have another DSP-10 which I 
will be able to compare with once I get the KDSP talking with the 
DSP-10.  It doesn't like the lower signal voltages and the KDSP interface 
is the older one.

I will give the short across C113 a try and see if it cleans up the 
signal.  That should also be a good test for mine. I do have a 200MHz scope 
so I should also be able to see if there is any noise on the loop circuit.

Lee - AA1YN

At 05:36 PM 3/28/2006 -0800, you wrote:
>Hi Lee,
>
>I agree, something is quite wrong!!
>
>I dropped a loop near the 127 MHz Osc ( I moved up to get roughly the 
>tuning voltage you have) and snapped a picture of the spectrum analyzer:
>http://www.proaxis.com/~boblark/127mz1.jpg
>
>This was done with the BW I had available, 100 Hz, as I don't have 300 
>Hz.  But  BW=1 kHz looks clean also. There was nothing to see outside of 2 
>kHz/div so I
>
>Maybe loop filter components? Possibly, but not likely the PLL IC.  Maybe 
>someone else has ideas.
>
>Also, the spectrum to the right  in the unlocked pix seems strange. How 
>did you achieve "unlock?" Maybe this is the residual on the phase detector 
>output.
>
>I will pursue this further, after dinner.
>
>73,.  Bob W7PUA
>
>At 04:43 PM 3/28/2006 -0500, you wrote:
>>I have been playing around some with an HP 141T spectrum analyzer I just 
>>purchased and have been looking at the local oscillators.  While the 
>>19MHz osc looks fairly clean, the 124MHz osc does not. As a mater of 
>>fact, it is pretty bad in my opinion.  I don't know if anyone else has 
>>had the opportunity to look at theirs but I've put up a web page on my 
>>web site showing what I've found.
>>
>>When taking the measurements, I've removed the coax jumpers from the 
>>outputs of the oscillators and used a pigtail coax with an SMA connector 
>>to get the signals to the analyzer.
>>
>>The URL is http://www.aa1yn.com/dsp-10/spec_ana/ and the images are 
>>linked to medium resolution images.
>>
>>Any thoughts? Any questions? Any ideas?
>>
>>
>>Lee Scott - AA1YN http://www.aa1yn.com
>>Home of the VHF & Up Register http://www.aa1yn.com/vhf
>>Home of the VHF Talk chatroom http://vhftalk.aa1yn.com
>>Hooksett, NH
>>FN43gc52
>>
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