Hummm, the Noise Blanker on my R4C (unmodified) seems to work better at eliminating the noise I have around my house better than my Icom IC-775DSP which is a great radio with IF-DSP so I would say my unmodified R4C works very well.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Don Jones Sent: Tuesday, February 01, 2011 4:10 PM To: [email protected] Subject: Re: [Drakelist] Wanted 4NB Noise Blanker KO7I RESPONSE - "The CW roofing filter is particularly bad... but the 4NB is good..." SAY WHAT? I could not disagree with you more. A unmodified R-4C has a Narrow Spaced Dynamic Range of 58dB while the Sherwood modified R-4C has a dynamic range of 84dB. So in affect what you have just said is that having a noise blanker that works is more important than having your receiver blown away by adjacent QRM. I'll take the roofing filter thank you. :-) FWIW, the mod's to my "Sherwood R-4C" do allow you to use the standard 6kHz front end filter. The 4NB noise blanker has only been marginally successful, at best, even when I revert to the standard filters. Don Jones KO7i Message: 1 Date: Tue, 01 Feb 2011 16:26:07 -0500 From: Garey Barrell <[email protected]> To: [email protected] Subject: Re: [Drakelist] Wanted 4NB Noise Blanker Message-ID: <[email protected]> Content-Type: text/plain; charset=windows-1252; format=flowed Don - You answered your own question/statement. I believe the words 'heavily modified' were tossed around! :-) The Sherwood mods essentially render the 4NB useless, as you have discovered. The CW roofing filter is particularly bad, as it narrows the noise bandwidth seen by the NB, and delays pulses through it so they no longer match up with the blanking pulses. The NB is very effective as some have stated, when used with the original receiver topology. Like so much in the world of RF and electronics in general, a receiver is a 'system'. The original design was optimized (within cost constraints) as a whole. Anything that alters that design takes the risk that it 'may' alter that basic, optimized design, 'possibly' improving one characteristic. Unfortunately the characteristic it improves almost always causes another characteristic to decline, perhaps obviously, otherwise not so much. The basic Drake NB is the same design from the R-4A through the R-7, and most find them VERY effective on high level, short duty cycle impulse noise. As soon as the noise pulses are 'stretched', either by source characteristics or group delay through filters, the effectiveness drops off quickly. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs <www.k4oah.com> _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
