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564keying [2011/11/07 13:01]
n1eu
564keying [2011/11/07 13:05]
n1eu
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-====== Omni 6+ CW Keying Improvement Discussion ======+======= Omni 6+ CW Keying Improvement Discussion ​=======
  
-//In 1998-1999, an extremely informative investigation took place on the Ten-Tec reflector concerning the quality of the Omni 6+ cw transmit signal and cw sidetone. Out of this investigation came a few suggested mods as well as the introduction of the Inrad 2.8Khz filter as a substitute for the stock 2.4Khz filter. W9AC was the principal contributor,​ and I've quoted some of his key postings below - N1EU//+  
 + 
 + 
 +//In 1998-1999, an extremely informative investigation took place on the Ten-Tec reflector concerning the quality of the Omni 6+ cw transmit signal and cw sidetone. Out of this investigation came a few suggested mods as well as the introduction of the Inrad 2.8Khz filter as a substitute for the stock 2.4Khz filter. ​**W9AC** was the principal contributor,​ and I've quoted some of his key postings below - N1EU// 
 + 
 +=== 9/6/98 ===
  
-9/6/98 
 Anyway, I continue to enjoy my Omni 6+ for real CW work, particularly since I made my keyed waveform and chirp mods back in June, and eliminated the slight QSK "​thump"​ altogether. The last mod makes a tremendous improvement and requires a non-invasive mod to only one wire on the I.F./A.F. Board. Everyone should at least try this since it can be restored simply with the push of a connector. Anyway, I continue to enjoy my Omni 6+ for real CW work, particularly since I made my keyed waveform and chirp mods back in June, and eliminated the slight QSK "​thump"​ altogether. The last mod makes a tremendous improvement and requires a non-invasive mod to only one wire on the I.F./A.F. Board. Everyone should at least try this since it can be restored simply with the push of a connector.
  
 By now, I thought the W1AW 20-meter signal would have improved. While listening tonight, the leading edge chirp is clearly evident. I don't mean to start another raging discussion on this, but it's evident that some Omnis manifest this slight chirp. Hint: the source can be traced to the 9 MHz @ 2.4 kHz crystal filter circuit. This is the only filter that shares the TX and RX function. Those radios with chirp are the same radios that exhibit a truncated trailing CW waveform, particularly when adjusted to the most "​soft"​ setting. The new Omni 6+ SMD Control Board no longer allows you to make this adjustment. Instead, a fixed resistor is now located where a pot used to reside and guess what? The fixed value corresponds to what used to be the most "​hard"​ setting. Here's another hint for Ten-Tec: The source of the chirp is what also causes the USB receive audio to sound a bit thinner in low-end response and less "​full"​ than in LSB. Has anyone else noticed this? The good news is that the chirp is correctable. Anyway, compare the 20-meter signal against the simultaneous 40-meter transmission. By now, I thought the W1AW 20-meter signal would have improved. While listening tonight, the leading edge chirp is clearly evident. I don't mean to start another raging discussion on this, but it's evident that some Omnis manifest this slight chirp. Hint: the source can be traced to the 9 MHz @ 2.4 kHz crystal filter circuit. This is the only filter that shares the TX and RX function. Those radios with chirp are the same radios that exhibit a truncated trailing CW waveform, particularly when adjusted to the most "​soft"​ setting. The new Omni 6+ SMD Control Board no longer allows you to make this adjustment. Instead, a fixed resistor is now located where a pot used to reside and guess what? The fixed value corresponds to what used to be the most "​hard"​ setting. Here's another hint for Ten-Tec: The source of the chirp is what also causes the USB receive audio to sound a bit thinner in low-end response and less "​full"​ than in LSB. Has anyone else noticed this? The good news is that the chirp is correctable. Anyway, compare the 20-meter signal against the simultaneous 40-meter transmission.
  
-9/7/98+=== 9/​7/​98 ​===
 The mod consists of unplugging connector 52 on the I.F./A.F. Board. That's it. Plug 52 should have only one wire attached to it. Those of you with more recent Omni Sixes should verify this as some of the circuit boards have been changed to SMD types. Once connector 52 is unplugged, use a nylon tie-wrap to keep it safely out of harm's way. The mod consists of unplugging connector 52 on the I.F./A.F. Board. That's it. Plug 52 should have only one wire attached to it. Those of you with more recent Omni Sixes should verify this as some of the circuit boards have been changed to SMD types. Once connector 52 is unplugged, use a nylon tie-wrap to keep it safely out of harm's way.
  
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 This is not a Ten-Tec approved modification. I discovered this while making other modifications to my Omni Six Plus. Use care in making this change if you attempt to make it. This is not a Ten-Tec approved modification. I discovered this while making other modifications to my Omni Six Plus. Use care in making this change if you attempt to make it.
  
-9/20/98+=== 9/​20/​98 ​=== 
 Yes, the 20-meter W1AW signal does not do justice to the Omni Six/Six Plus, and I do not believe it is representative of most Omnis. Yes, the 20-meter W1AW signal does not do justice to the Omni Six/Six Plus, and I do not believe it is representative of most Omnis.
  
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 As you can see, it's a lot of work to make the rig sound gorgeous. For me, it was worth it. Others will undoubtedly disagree. I hope this helps. As you can see, it's a lot of work to make the rig sound gorgeous. For me, it was worth it. Others will undoubtedly disagree. I hope this helps.
  
-10/7/98+=== 10/​7/​98 ​=== 
 Those of you who have an Omni Six/Six Plus that exhibit a slight transmitted CW chirp may be in for some good news. George, W2VJN at INRAD has agreed to manufacture a 2.8 kHz BW 9 MHz I.F. filter if we can demonstrate enough of a demand for it. This is a replacement filter for the stock 2.4 kHz BW 9 MHz filter. This is the only filter in the Omni that shares the receive and transmit function. This same filter also exacerbates the slight chirp caused by frequency-shift-keying the Omni's 9 MHz BFO circuit board on some Omnis. Those of you who have an Omni Six/Six Plus that exhibit a slight transmitted CW chirp may be in for some good news. George, W2VJN at INRAD has agreed to manufacture a 2.8 kHz BW 9 MHz I.F. filter if we can demonstrate enough of a demand for it. This is a replacement filter for the stock 2.4 kHz BW 9 MHz filter. This is the only filter in the Omni that shares the receive and transmit function. This same filter also exacerbates the slight chirp caused by frequency-shift-keying the Omni's 9 MHz BFO circuit board on some Omnis.
  
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 If you have an interest in this, please e-mail me directly and I will forward your commitment to George. Thanks. If you have an interest in this, please e-mail me directly and I will forward your commitment to George. Thanks.
  
-1/3/99+=== 1/​3/​99 ​=== 
 In a nutshell, more or less, Ten-Tec'​s stock 2.4 kHz filter in the 9 MHz IF slot will excerbate a slight chirp eminating from the 9 MHz BFO circuit board. From my experiments earlier this summer, the degree of note degradation is a function of two factors: 1) Some Omni Sixes have a BFO which exhibits a slight degree of chirp, most don't. This can be confirmed by tuning an external receiver to 9 MHz and lightly coupling the BFO to the external receiver. 2) If the 2.4K filter has a sharp knee at the Omni Six's CW transmit BFO frequency of 9,000.400 kHz, the filter will not only magnify the effct of the chirp, but passing this frequency through the filter'​s sharp lower skirt can lead to a distorted CW waveform whose trailing edge becomes slightly truncated. I confirmed that the 2.4K filter was the sole contributor to this effect by augmenting the CW transmit BFO frequency slightly upward by 100 Hz, then downward by 100 Hz. On my particular Omni, a BFO frequency adjusted ever-so-slightly out of spec (or from drift) will cause noticable visual distortion of the waveform and audibly, this is when the note becomes dirty and soft. It bears pointing out that chirp is not the ONLY manifestation of poor 2.4K filter quality control. In a nutshell, more or less, Ten-Tec'​s stock 2.4 kHz filter in the 9 MHz IF slot will excerbate a slight chirp eminating from the 9 MHz BFO circuit board. From my experiments earlier this summer, the degree of note degradation is a function of two factors: 1) Some Omni Sixes have a BFO which exhibits a slight degree of chirp, most don't. This can be confirmed by tuning an external receiver to 9 MHz and lightly coupling the BFO to the external receiver. 2) If the 2.4K filter has a sharp knee at the Omni Six's CW transmit BFO frequency of 9,000.400 kHz, the filter will not only magnify the effct of the chirp, but passing this frequency through the filter'​s sharp lower skirt can lead to a distorted CW waveform whose trailing edge becomes slightly truncated. I confirmed that the 2.4K filter was the sole contributor to this effect by augmenting the CW transmit BFO frequency slightly upward by 100 Hz, then downward by 100 Hz. On my particular Omni, a BFO frequency adjusted ever-so-slightly out of spec (or from drift) will cause noticable visual distortion of the waveform and audibly, this is when the note becomes dirty and soft. It bears pointing out that chirp is not the ONLY manifestation of poor 2.4K filter quality control.
  
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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 ​=== 
  
 Perhaps ALL Omni-VI can be fixed that way. E.g. crank in more >shift until they are clean. TRY IT! Perhaps ALL Omni-VI can be fixed that way. E.g. crank in more >shift until they are clean. TRY IT!

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