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564keying [2011/11/07 13:05] n1eu |
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| The INRAD 2.8 kHz filter for the 9 MHz IF position was designed to provide for the same degree of passband freedom as that designed into the Omni V. The choice of 2.8 kHz was not arrived at recklessly. I wanted to duplicate the excellent CW characteristics of the Omni V. Becuase of the Omni Six's fixed CW transmit BFO of 9,000.400 kHz, nothing less than 2.8 kHz will do unless the filter is manufactured with exceptional QC standards. A side benefit of the INRAD filter is that the USB/LSB passband is much more predictable and symmetrical. There's an easy test to confirm filter asymmetry: if USB receive audio sounds slightly "thinner" than than that heard in LSB, you've got a defective 2.4 kHz filter. | The INRAD 2.8 kHz filter for the 9 MHz IF position was designed to provide for the same degree of passband freedom as that designed into the Omni V. The choice of 2.8 kHz was not arrived at recklessly. I wanted to duplicate the excellent CW characteristics of the Omni V. Becuase of the Omni Six's fixed CW transmit BFO of 9,000.400 kHz, nothing less than 2.8 kHz will do unless the filter is manufactured with exceptional QC standards. A side benefit of the INRAD filter is that the USB/LSB passband is much more predictable and symmetrical. There's an easy test to confirm filter asymmetry: if USB receive audio sounds slightly "thinner" than than that heard in LSB, you've got a defective 2.4 kHz filter. | ||
| - | (**K0CQ** comment) | + | //(**K0CQ** comment) |
| 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 | 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. | + | 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.// |
| === 1/4/99 === | === 1/4/99 === | ||
