[DSP-10] CW transmit has a raspy sound

[Lee Scott - AA1YN]

Bob,

I've done a little more -

Note that in all I've done so far, the PLL was not running - ie it was not 
programmed. As a matter of fact, the KDSP-10 is not even connected.

As soon as I read this reply from you, I realized by shorting C113, you 
eliminate the PLL as a source of phase noise all together.  I am in the 
process of building a DSP-10 for NG4C and it is at the stage where I can 
operate the 124MHz osc so I shorted C113 on both DSP-10s.  I've posted the 
results on my website.  I also shorted R152 on mine so it would eliminate 
any noise coming from the varicap diodes but only saw a slight improvement.

At this point, the only components I think I can suspect is the two 
capacitors C117 and C118.  I changed the values of these as the oscillator 
would not operate at the proper frequency.  I chose a value of 5pf for C117 
and 22pf for C118.  I kept the ratio of the two the same.  Perhaps this is 
the problem??? I used some Panasonic capacitors. They are NPO 50v ceramic 
caps.  Do they need to be something special or a better grade? Should I 
have just reduced maybe C118 and kept C117 at 10pf? What values did you end 
up using on your circuit?

I remember the discussions on this reflector before about the osc being too 
low in freq and I know others have reduced these caps to get the circuit to 
tune properly. Since some others are having the same complaints about the 
quality of the signal, I would suspect they are having the same problem. I 
am willing to give anything a try.

Lee - AA1YN

At 08:50 PM 3/28/2006 -0800, you wrote:
>I posted the second picture of the 126 MHz oscillator, free-running, at
>http://www.proaxis.com/~boblark/127mz2.jpg
>You can see that it has picked up some 5 kHz modulation , but otherwise is 
>clean.  The 5 kHz is likely stray pickup from the PLL IC that is still 
>running. The output of the phase detector is removed by a wire across 
>C113. The frequency at this voltage has moved down to about 123 MHz.
>
>73, Bob W7PUA
>
>At 05:52 PM 3/28/2006 -0800, you wrote:
>>One more test---I just made the 126 MHz osc free run by a short across 
>>C113. It looked reasonably clean at 5 kHz/div and 1kHz BW. Much, much 
>>cleaner than what I see in your SA shot.. Later, I will post it for reference.
>>
>>Good luck,
>>  Bob
>>
>>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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>>
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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