Don, et al. my audiologist told me that when I get my new hearing aid, I can hear way past 10,000 cycles. I cannot wait to hear those expanded frequencies coming from enhanced audio modulators. Bring it on!! And, who said that growing old doesn't have its advantages!
David Knepper, W3ST-W3CRA Publisher of the Collins Journal and Secretary to the Collins Radio Association www.collinsra.com -------Original Message------- From: D. Chester Date: 9/20/2009 1:44:12 AM To: amradio@mailman.qth.net Subject: Re: [AMRadio] AM Transmitter "quality" > I don't need to send or hear anything above and below about 100 Hz to 4000 > Hz, but extending the response well beyond those points cleans up the > audio > to those points. > If you build a rig that only goes 300 to 2800, the distortion at 300 and > 2800 is usually high. > Brett N2DTS The old UTC linear standard series catalogues recommend transformers to have a flat response at least one octave above and one octave below the target frequency response, to bring phase shift distortion to an acceptable level. To achieve reasonably good audio quality at the legendary 300-3000~ frequency range, your audio chain needs to be capable of flat response, at the very minimum, from 150 to 6000 Hz. This is necessary to preserve the original audio waveform, and substantially reduces listener fatigue. Using broadcast quality audio transformers (UTC LS- series or better) and "hi-fi" circuit design without negative feedback, my homebrew transmitters test flat and relatively distortion-free from about 40~ to 11,000~. That means they are really optimum only for 80-5500 Hz. That explains why so many vintage AM broadcast transmitters were designed with such a tremendously wide frequency response, 30-15K or better, even though everyone knew there were few, if any, AM receivers in existence with anywhere near that good a frequency response. The designers were actually shooting for an optimum range of about 60-7500 Hz, pretty much typical for a good quality AM broadcast signal. I recall when I was working in broadcast engineering in the mid-60's, the bare-bones minimum acceptable standard for an FCC proof of performance was 100Hz to somewhere between 5000 and 7500 Hz. I forget now if the exact high frequency number was 5, 6 or 7.5K. Don k4kyv _______________________________________________________________ This message was typed using the DVORAK keyboard layout. http://www.mwbrooks.com/dvorak/ http://gigliwood.com/abcd/ ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list Searchable Archives: http://www.mail-archive.com/amradio@mailman.qth.net/ List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Post: AMRadio@mailman.qth.net To unsubscribe, send an email to amradio-requ...@mailman.qth.net with the word unsubscribe in the message body. This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
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