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563inradaud [2011/08/24 16:52]
n1eu
563inradaud [2011/09/02 16:27]
n1eu
Line 17: Line 17:
 ==== 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 ​used both of the following ​with good results ​(preferred the second method 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 ​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 ​+  2. Behringer PEQ 2200 analog parametric equalizer set for 85khz lo cut, 2.5khz hi cut, band5 eq -15dB 10khz 1.2 octaves ​  OR 
 +  3. 4Khz Low Pass filter circuit designed by Elecraft for use in the K3  OR 
 +  4. Low Pass filter circuit (fig. 3.50) from Experimental Methods in RF Design, with each capacitor value scaled down by 50%
   ​   ​
-A side benefit of this technique ​is that all the digital "​grunge",​ encoder noise, and other annoying artifacts are totally removed from the rx audio +The advantage to filter methods 3 & 4 is that they can easily be incorporated internal to the Omni6.
  
-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.+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. ​ 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.

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