> Only Elecraft can answer this question. In early 2008, I tried using a 1 > kHz filter for CW TX (telling the configuration it was a 2.7) for CW TX > and > got some very bad signal quality reports.
If the CW Tx frequency is not reasonably centered in the filter passband, poor keying quality reports will result, especially if placed on, or near the upper or lower skirt of a crystal filter. This asymmetrical group delay issue plagued the Omni VI+ as the CW carrier frequency was placed right on the skirt of the 2.4 kHz @ 9 MHz filter. The placement of the Tx BFO frequency near the filter skirt was done in order to better accommodate variable CW Tx offset in the Omni 6+ design. In the Omni V, the CW BFO was fixed and located about 400 Hz above where Ten Tec placed it in the Omni 6+. That shift of a few hundred Hz made all the difference in the world. Among several other contributions to poor keying in the Omni 6+, including a poor ALC design that mutated from the Omni 5 and 6 (non plus), the primary culprit was the BFO placement near the skirt of the filter. The overall solution included filter replacement with a custom 2.8 kHz filter from INRAD and re-working the ALC with a handful of components. I ended up bypassing the filter with a hard wire in CW Tx. Passing the BFO through the filter simply isn't required when the rig is capable of generating a clean waveform. Plenty of old homebrew boatanchor rigs were capable of producing a high-quality RF envelope and didn't rely upon ALC nor a filter to pass the CW waveform. True, just as many homebrew rigs produced horrendous signals on the air. Since keying bandwidth is a function of the RF envelope shape, I'm not sure why anyone would want to narrow the K3 filter on CW transmit. As long as the ALC is stabilized and the slope is reasonably smooth and absent sharp discontinuities, all a narrower filter will accomplish is to produce envelope distortion if not placed squarely in the center of the filter passband. Paul, W9AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
