[DSP-10] CW transmit has a raspy sound

Tue Dec 20 14:10:47 EST 2005

Here's what I found out so far,

I have the spurious sidebands on the 19.68MHz osc with the covers off or 
on.  I re-adjusted C69 to ensure tuning voltage was at 4.0v. I turned off 
all power supplies, florescent lights, and CRT monitors.  Ran the setup 
under battery power and used the FT817 as a monitor.  The sidebands are 
still there - maybe more so but it all depends on the antenna position for 
the 817. Hard to keep things so exact. Anyway, I've put up a couple more 
wave files.

I checked the VCO voltage on the 126MHz osc.  I can get the phase noise to 
a minimum with the voltage set at about 0.8v.  Anything above/below that - 
there is a lot more phase noise.  I then re-adjusted the voltage to 3.5v at 
a freq of 147MHz.

On most all recordings I've made of the local oscs, I turn off the laptop 
after I start recording and towards the end of the recording, I turn off 
the DSP-10 to ensure what I am listening to is coming from the DSP-10 and 
not some external signal.

The new recordings are using Spectran.

One thing I did accidentally discover is +/- 15KHz and +/= 30KHz, there are 
image birdies.  Using Spectran, the CW output at 144.121.690 to be -38dB 
and at 144.136.690 (or 144.106.69) the output is -47dB. Quite a hefty 
signal. This was with an external antenna on the FT-817.  When I connected 
the DSP-10 directly to the FT-817, the signal was not there - may be a 
non-issue.

The new 19.68MHz recording are labeled 19680-osc-ext-ft817-1.wav (-2) or (-3).

A CW recording labeled dsp10-xmit-pwr-ft817-1.wav, I connected the DSP-10 
xmit out thru 70dB of attenuation to the FT817 input. I started the xmit 
pwr at 13 and ran it up to 60 and back down (1/2 to 1 sec steps).

There is also a cw-test-ext-ft817.wav with morse code at 10wpm and 5wpm 
followed by a CW. This was done with 70dB attenuation and an xmit pwr of 40.

If you have any ideas or need more recordings, let me know.

Lee - AA1YN

At 01:59 PM 12/19/2005 -0800, you wrote:
>Hi Lee -
>
>I'll send this to the group, as there may be others that are interested, 
>or that might have suggestions.
>
>At this point, I just ran your WAV files through Spectran and looked at 
>the spectrum. You might try this to see as we will all see the same thing, 
>and it also plays the sound to let you correlate the observations.
>
>When I look at the SSB spectrums, I see a triple spectrum, the voice, and 
>a replica 120 Hz above and below.  Also, the 19680 signal has the same 
>side bands.
>
>This is probably not from the power supply, as there doesn't seem to be 
>any AC from the mike preamp (at 120 Hz), but rather as modulation side 
>bands only.  My guess is that the 19.68 osc is getting modulated by a 
>local magnetic field from a power supply. Try moving the box and see what 
>happens. The 19.68 core does not have a magnetic cover and I have seen 
>this effect before.  Everyone should be careful about sitting the DSP-10 
>on top of a power supply, or other magnetic radiators.
>
>The second observation, is that  the CW signal might have above average 
>phase noise. Try tuning the 126 Mhz VCO slightly lower in frequency and 
>see what happens. If the VCO control voltage is too low, it gets low loop 
>gain and poor control from the PLL.
>
>Let us know!
>
>73,
>Bob  W7PUA
>
>
>At 08:10 AM 12/18/2005, you wrote:
>>Hi bob,
>>
>>I've uploaded some wav files to my server.  The URL is
>>http://www.aa1yn.com/dsp-10/wav/
>>
>>Let me know if you need/want any more.  The file names should be self 
>>explanatory but I can clarify any.
>>
>>You can contact me directly via email - aa1yn at aa1yn dot com
>>
>>Lee - AA1YN
>>At 03:04 PM 12/13/2005 -0800, you wrote:
>>>Hi Lee -
>>>
>>>None of the local folks have this. Ron has this problem. Could either of 
>>>you provide a WAV file of this over the air??  Or scope pictures of the 
>>>drive to the transmit mixer?  I really am puzzled.
>>>
>>>Thanks,
>>>Bob W7PUA
>>>
>>>At 02:16 PM 12/13/2005, you wrote:
>>>>One problem I have always had with my DSP-10 is a very raspy sounding 
>>>>CW or Sideband signal on the air.  Anyone else have this and has anyone 
>>>>else solved this?
>>>>
>>>>
>>>>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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>>>>DSP-10 mailing list
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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