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563ssbaud [2011/10/15 15:00] n1eu |
563ssbaud [2012/12/10 19:46] n1eu [Omni 6 DSP Bypass Mod] |
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| ==== Omni 6 DSP Bypass Mod ==== | ==== Omni 6 DSP Bypass Mod ==== | ||
| - | To get around the 260hz high pass filtering of the Omni 6 dsp and still provide the needed low pass hiss filtering, I have done the following with great success: tap the Omni 6 audio right at the product detector output (pin 6) through a 1uF cap and bring it via shielded cable (you could also tap the audio after the notch filter) into an appropriate low pass filter to remove hiss. This can be an external equalizer/dsp unit or a homebrew op-amp circuit placed adjacent to the IF/AF board. I've tried both these methods with excellent results. | + | The key to getting good sounding ssb receive audio on the Omni 6 is to bypass the dsp. I routinely bypass both the dsp and the notch filter. However, you need to add some low pass filtering if you do this or the audio will contain an inordinate amount of hiss. Tap the product detector output (U3 pin 6) through a 1uF cap and then apply low pass filtering. I've done this both inside the Omni 6 (with homebrew 3Khz low pass filter) and outside the Omni 6 (with DSP-599ZX or Behringer equalizers). Inside the Omni 6, you can then send the output of the low pass filter to the AF Gain control and then to the audio amp by splicing into connector 55. This way, you can leave the dsp sidetone circuit intact. The result is a TOTAL transformation of the Omni 6 ssb receive audio. |
| A side benefit of this filtering technique is that all the digital "grunge", encoder noise, and other annoying artifacts are totally removed from the rx audio. | A side benefit of this filtering technique is that all the digital "grunge", encoder noise, and other annoying artifacts are totally removed from the rx audio. | ||
| - | The existing audio chain can be left intact as well, in case you ever want to listen through the Omni 6 headphone jack or speaker. I considered reinjecting the low pass filtered audio back into the Omni 6 audio chain in the vicinity of DSP return connector 54/56 on the IF/AF board, but the Omni 6's af output amplifier U8 has very poor low frequency response. | + | Coupling the dsp bypass mod with installing dual Inrad 2.8khz filters will transform the Omni 6 ssb rx audio from mediocre to sublime. Although rx audio is the topic at hand, I've also optimized my tx audio by feeding line level (i.e., externally pre-amped) tx audio into the balanced modulator U4-5 through a 1uF cap and a 10K resistor. This mod leaves the existing Omni 6 tx audio chain intact. |
| - | + | ||
| - | Coupling the dsp bypass mod with installing dual Inrad 2.8khz filters will transform the Omni 6 ssb rx audio from mediocre to sublime. Although rx audio is the topic at hand, I've also optimized my tx audio by feeding line level (i.e., externally pre-amped) tx audio into the balanced modulator U4-5 through a 1uF cap and a 1.5K resistor. This mod leaves the existing Omni 6 tx audio chain intact. | + | |
| - | + | ||
| - | One last project for the future is to implement a ssb monitor by feeding some of the tx audio through the unused analog switch U7D in parallel with the cw sidetone audio. | + | |
| - Barry N1EU | - Barry N1EU | ||
