[DSP-10] CW transmit has a raspy sound

[Lee Scott - AA1YN]

Hi Mike,

I'll reply to the reflector.

I wish I had another 50dB of attenuation but with one 20dB/75w attenuator 
followed by 2 20dB attenuators followed by 2 10dB attenuators, I could only 
muster 70dB of attenuation.  The idea was to get the xmit signal directly 
from the dsp-10 to the ft-817. A couple of 40dB or 50dB attenuators are on 
the wish list.

The project has been around for a couple of years but the EasyKit Lite went 
flaky after 3 months so I set it aside.  Finally bought a KDSP-10x for it.

The basic CW problem has been around from the start.  I built a DSP-10 for 
a couple of others and have not had the problem with them that I know of. 
Unfortunately mine was not working at the time I built the others so I 
couldn't compare.  As luck would have it, I will be building a forth DSP-10 
starting next week for another and this will also have the KDSP-10x 
processor. Probably in about 4 weeks or sooner, I'll have another to 
compare. Depends on whether my customers leave me alone (self employed).

As far as the CW sidetone, it sounds ok to me. A good steady single tone. 
Since it is coming out of the DS Processor as audio, I would expect it to 
sound ok.

One thing I did notice. With the old EasyKit Light the noise floor was 
about -153dB and with the new KDSP-10, the noise floor is up around -147dB.

I didn't think there would have been any problem with power supplies but I 
had to go through the battery route to eliminate it.

As far as rcv signals go, I did try a 1/2w CW from the FT-817 into a dummy 
load and you could see the +/-120Hz sidebands on the receive signal at the 
DSP-10 end so it is both ways.  This should be the result since the 
19.68MHz lo is used for both xmit and rcv.

Lee - AA1YN

At 12:00 PM 12/20/2005 -0800, you wrote:
>Hi Lee,
>
>There is an issue with using reduced transmit power settings. There is 
>always a level of noise in any amplifier chain, and the DSP-10 is no 
>exception. The power control is at the start of the amp/filter/mixer 
>chain, so reducing power results in a degraded S/N in the output. For 
>levels down to 55-60, this is not a huge problem, but it is something to 
>be aware of. Recovered signals of low power setings may show a degraded 
>S/N when captured in an audio file. This doesn't reflect on actual 
>performance at normal settings, it's just how it is, and something to keep 
>in mind.
>
>It might be better to use a dummy load on both the DSP-10 and the monitor 
>receiver. There should be plenty of signal available and gains can be run 
>at a level closer to "real" life.
>
>I should have enquired earlier, but wonder where this projects stands. Is 
>this just getting going ? Had it for years and it's always been this way ? 
>Are there other functions that seem abnormal ? Does CW sidetone sound OK ? 
>Everything works great but receive audio sounds fuzzy ? Receive sounds OK, 
>but the transmitted signal is bad ? Waterfall display is normal ? 
>Waterfall has birdies all over ?
>
>Have you ever had an opportunity to observe someone elses DSP-10 ?
>
>There were 7 of our local DSP-10 gang chatting about your problem this AM 
>on 80 meters. The magnetic field theory didn't get much supoport. 
>Observations were that the DSP-10 had to be SITTING on the power supply to 
>have any effect. This is supported by my observations with a Weller 
>soldering Gun a few inches away from the DSP-10. A foot away, and there 
>was no observable effect. Fluorescent lights also seem unlikely, but no 
>one had any experience with that.
>
>73 Mike KD7TS
>
>
>
>


Lee Scott - AA1YN http://www.aa1yn.com
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