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563inradaud [2011/08/27 21:31] n1eu |
563inradaud [2011/09/02 16:25] n1eu |
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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 external to the Omni 6 via shielded cable (you could also tap the audio after the notch filter) AND feed this audio line into an appropriate low pass filter to remove hiss. I've personally tested 1-3 of the below methods with good results (2-4 are preferred due to smoother sound): | + | 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. Below is a list of some ideas for implementing the low pass filter. I've personally tested methods 1-3 with good results, although I tend to favor analog filtering. |
1. Timewave DSP-599ZX high Z input B set to 0.0dBV, filtering set for 100-2800hz OR | 1. Timewave DSP-599ZX high Z input B set to 0.0dBV, filtering set for 100-2800hz OR | ||
2. Behringer PEQ 2200 analog parametric equalizer set for 85khz lo cut, 2.5khz hi cut, band5 eq -15dB 10khz 1.2 octaves OR | 2. Behringer PEQ 2200 analog parametric equalizer set for 85khz lo cut, 2.5khz hi cut, band5 eq -15dB 10khz 1.2 octaves OR | ||
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4. Low Pass filter circuit (fig. 3.50) from Experimental Methods in RF Design, with each capacitor value scaled down by 50% | 4. Low Pass filter circuit (fig. 3.50) from Experimental Methods in RF Design, with each capacitor value scaled down by 50% | ||
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- | The advantage to filter method 3 is that it can easily be incorporated internal to the Omni6. | + | The advantage to filter methods 3 & 4 is that they can easily be incorporated internal to the Omni6. |
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 is left intact as well, in case you ever want to listen through the Omni 6 headphone jack or speaker. Another option for the experimenter is to re-inject the externally filtered audio back into the Omni 6 which would be easily accomplished via the DSP return connector 54/56 on the IF/AF board. | + | 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. Another option for the experimenter is to re-inject the externally filtered audio back into the Omni 6 which would be easily accomplished via the DSP return connector 54/56 on the IF/AF board. |
Coupling the dsp bypass mod with installing dual Inrad 2.8khz filters will transform the Omni 6 ssb rx audio from mediocre to superb. Although rx audio is the topic at hand, you may want to consider feeding the tx audio directly into the Omni 6 balanced modulator (U4-5 on TX Audio board) via a 1uF capacitor if you are already using an external mic preamp and can adjust its output to a fairly low level. | Coupling the dsp bypass mod with installing dual Inrad 2.8khz filters will transform the Omni 6 ssb rx audio from mediocre to superb. Although rx audio is the topic at hand, you may want to consider feeding the tx audio directly into the Omni 6 balanced modulator (U4-5 on TX Audio board) via a 1uF capacitor if you are already using an external mic preamp and can adjust its output to a fairly low level. |