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
>>
>>--
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>>
>>
>
>
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>
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