The add on DSP units are audio DSP filters and they can be very effective. The OMNI VI+ has a very effective one. They can be used with or without the roofing filter in the first IF. As there are various needs for cw and for SSB, the roofing filter will also change. So, for ssb, a 3KC filter would be good, the 600 cycle or lower for cw would be applicable. All the roofing filter does is to limit the necessarily wide bandwidth of the front end from abusing the first IF and later stages. When this happens, IMD occurs and other strange generated noises are present that travel thru the set. Stopping the mess at the first IF allows the rest of the radio to perform efficiently and cleanly. The noise filter on the audio, only helps when some crud does slip into the roofing filter passband. Sherwood sells a switch kit that varies the AGC and has a concentric switch that can select one or more of the roofing filters. You do not have to elect to have a cw or ssb filter only; with the switch you can have what you wish, even both. So, if you want optimal, get the roofing filter for the mode or modes that you want and if necessary (generally only occasionally) get the audio DSP. Note that in most models, the roofing filter can be switched with an unused lug on the filter switch. You will need to look/see if you have this. Good luck. David Assaf, III W5XU From: drakelist-boun...@zerobeat.net [mailto:drakelist-boun...@zerobeat.net] On Behalf Of Hunter Ellington Sent: Saturday, February 05, 2011 5:29 PM To: drakelist@zerobeat.net Subject: [Drakelist] DSP Filters My experience is just the opposite. I use a Timewave S9+ with both my R7 and R4C. The Time waves work splendidly with my Drakes, and reduce noise to the point that these old receivers compare favorably with the modern rice boxes.. K0GFY R. Hunter Ellington 303-454-0543/720-560-8139 P.O. Box 44 Larkspur, CO 80118
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