The W1AW 20-meter CW signal is a perfect example of what we sometimes hear
from the Omni Six. Mine sounded identical to it prior to the mods.
Quite honestly Steve, I don't believe the ARRL's waveform presentation in
their product reviews is an accurate indicator of the perceived CW note.
Yes, the scope will show the dynamics of the keying, but nothing concerning
potential phase shift and frequency shift effects. When the CW BFO
frequency drops below the filter knee, the scope DOES show this. The
waveform becomes slightly distorted and the trailing edge of the waveform
becomes truncated.
Even with the Omni Six's deficiencies in this area, it's still nearly
miraculous that the Ten-Tec can make QSK work given the fat that it must
remain stable at large receive-to-transmit and RIT/XIT offsets. Actually,
I've gained a greater respect for the Omni Six while searching out its
problems. You begin to realize the practical constraints and compromised
made when fast QSK and frequency synthesizers are combined together. The
Omni V is an excellent example of how well this can work. With a little
extra help in the BFO and 2.4K filter area, the Omni Six can sound every bit
as good as the V.. And yes, it shouldn't require user-made mods; it should
work this way out of the box.
Back to your original comment. Perhaps a new test should be developed to
measure keyed phase/frequency shift as a supplement to the portrayed keyed
waveform.
-Paul, W9AC
-----Original Message-----
From: Steve Ellington <n4lq@iglou.com>
To: Paul Christensen <paulc@mediaone.net>; geraldj@ames.net
<geraldj@ames.net>; David E. Shelton <w4des@iolky.com>
Cc: Roy Koeppe <royanjoy@ncn.net>; tentec@contesting.com
<tentec@contesting.com>
To: <tentec@contesting.com>
Date: Sunday, January 03, 1999 10:09 PM
Subject: Re: [TenTec] Re: N4LQ and the 2.8kHz Pill
>Here's something else I would like to know. The test performed by the ARRL
>lab include a keying waveform. The shape of the note looks great because
the
>chirp is a frequency shift and not an amplitude shift. (correct?)
>
>Now what kind of test with a scope would show the chirp? Obviously the ARRL
>blundered right past this since their 20m cw signal sounds like someone
>slapping a wet fish against hard concrete.
>
>
>
>>You hit the nail on the head Jerry. The effect of the CW transmit BFO
>>passing through the filter's steep knee not only exacerbates a slight
chirp
>>emanating from the Omni Six's BFO board, but there are audible group-delay
>>effects from phase change. Thanks for pointing this out.
>>
>>-Paul, W9AC
>>
>>-----Original Message-----
>>From: Dr. Gerald N. Johnson, P.E. <geraldj@ames.net>
>>To: David E. Shelton <w4des@iolky.com>
>>Cc: Roy Koeppe <royanjoy@ncn.net>; tentec@contesting.com
>><tentec@contesting.com>
To: <tentec@contesting.com>
>>Date: Sunday, January 03, 1999 6:17 PM
>>Subject: Re: [TenTec] Re: N4LQ and the 2.8kHz Pill
>>
>>
>>>
>>>The phase delay of a crystal filter changes rapidly at the knee. A
>>>little frequency shift could easily be magnified by that phase shift to
>>>sound like a wider chirp. It would seem to me to be best to make sure
>>>the CW signal was inside the filter a ways to get away from that. Either
>>>by selection of CW carrier frequency or filter frequency. Maybe it would
>>>be better to introduce a totally separate CW crystal oscillator that
>>>didn't need to go through the filter. I don't have any idea what that
>>>would do to the switching, but ought to make it sound perfect. Though
>>>its not easy to key a crystal oscillator without either clicks or
>>>chirps. The crystal doesn't like stopping and starting... Probably
>>>better to key a mixer to get a better on/off ratio that just keying a
>>>straight gain stage with the oscillator running continouously.
>>>
>>>73, Jerry, K0CQ
>>>
>>>--
>>>FAQ on WWW: http://www.contesting.com/tentecfaq.htm
>>>Submissions: tentec@contesting.com
>>>Administrative requests: tentec-REQUEST@contesting.com
>>>Problems: owner-tentec@contesting.com
>>>Search: http://www.contesting.com/km9p/search.htm
>>>
>>>
>>
>>
>>--
>>FAQ on WWW: http://www.contesting.com/tentecfaq.htm
>>Submissions: tentec@contesting.com
>>Administrative requests: tentec-REQUEST@contesting.com
>>Problems: owner-tentec@contesting.com
>>Search: http://www.contesting.com/km9p/search.htm
>>
>>
>
>
--
FAQ on WWW: http://www.contesting.com/tentecfaq.htm
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