In technical school after being a HAM for over 9 years I learned that it took 10Db change in level to perceive a doubling of audible signal level,,, 3 db hard to detect. I worked on modems during the Vietnam at a site for 1 year after tech school and all our old equipment was lab quality. I did this all day long for 6 days a week for a year. I know and heard what I write.
Bill K9YEQ K2-#35 (2 more), KX1-#35, K3, TS2000, IC7000, etc. > From: r...@cobi.biz > To: elecraft@mailman.qth.net > Date: Fri, 11 Dec 2009 14:16:54 -0800 > Subject: Re: [Elecraft] [K3] 150 watt "boots" for 160m > > Quite right Bill, in an audio laboratory or perhaps in a very quiet > telephone circuit. > > But radio communications is different according to what I learned in school, > lo' these many years past. Over half a century ago most radio communications > engineers began using 3 dB (2:1 power ratio) as the minimum change in a > signal level that would normally be just discernable to the listener, > considering typical band noise and QSB. That was based in actual on-the-air > observations by a great many operators over time. > > When considering changing my power level, I never consider it worthwhile to > change less than 3 dB and more typically 6 to 10 dB as the minimum worth > bothering with (e.g. shifting from a K2/10 at 10-15 watts CW to a K2/100 was > a just worthwhile shift). > > When I was much younger and more "innocent" I used to scramble for each > little watt, exulting in running 30 watts instead of 20 watts from a 6L6, > for example, or tweaking my 6146 rig to run 90 instead of 75 watts and > feeling sure that made a big difference. It sure seemed to produce more > results from calls. But, looking back over logs over time, it was clearly an > illusion.. > > That's when I acquired the sign that still hangs over my desk to remind me > that "Believing is Seeing". > > So I don't argue with people who want to make what is a quantifiable silly > choice. Instead I say, "If you want to do it and you believe it's worth it, > do it." > > I'm no different. After all, we humans make most of our choices based on > emotion and then we use rational logic to justify the choice. > > Ron AC7AC > > -----Original Message----- > >From 100 to 150, for 1.7 dB, when Bell Laboratories research (with > huge capital investment and telephone maintenance dollars on the line) > determined that 3 dB was the signal strength change discernment for > most people? > > I'm not sure who said 3 dB was the minimum detectable by a listener but I > believe it's incorrect. 1 dB "roughly matched the smallest attenuation > detectable to an average listener". (see below) > > "The decibel originates from methods used to quantify reductions in audio > levels in telephone circuits. These losses were originally measured in units > of Miles of Standard Cable (MSC), where 1 MSC corresponded to the loss of > power over a 1 mile (approximately 1.6 km) length of standard telephone > cable at a frequency of 5000 radians per second (795.8 Hz) and roughly > matched the smallest attenuation detectable to an average listener. Standard > telephone cable was defined as "a cable having uniformly distributed > resistances of 88 ohms per loop mile and uniformly distributed shunt > capacitance of .054 microfarad per mile" (approximately 19 gauge)." > > http://en.wikipedia.org/wiki/Decibel#History > > 73, Bill > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html _________________________________________________________________ Hotmail: Trusted email with Microsoft’s powerful SPAM protection. http://clk.atdmt.com/GBL/go/177141664/direct/01/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
