He cited the Fletcher Munson Curve, demonstrated in 1933 at Bell Laboratories, which showed that the human ear is most sensitive to frequencies in the range of 3-4 kHz, but the human voice has more energy in the lower frequency scales, dropping off rapidly at frequencies above 1000 Hz or so. With the "presence rise" bump in frequency response, his voice was far more intelligible over the PA set-up. He ran an A/B comparison between a flat frequency response setting on the amplifier, and incorporating a broad bump in response in the vicinity of 3000-4000 Hz. His forum topic was "What is wrong with our audio".
I have learned a lot, and you all have taught it to me.Īt his forum at the 2015 Huntsville AL hamfest, Bob Heil gave a demonstration using a portable PA system with one of his microphones. Yes, I know this is not essential ham radio, it is an extravagance. I now have that chance, and I would like to get on at least one band with a transmitter that can produce a broadcast sound. I always wanted to someday have a transmitter capable of producing similar audio that others would truly enjoy listening to, simply because it was easy and enjoyable to listen to. Nonetheless, when I lived in upstate New York, I remember listening to amateur stations such as K1JJ, W2INR, WA3VJB, W1CKI, WA3PUN, and others, who had that "broadcast" sound, and I truly enjoyed listening to their transmissions simply because they sounded so good. I am gratified that I was able to build from scratch a transmitter that other hams deem worthy of a good audio report, but it is still standard, basic amateur radio audio design, and I consider this to be appropriate design for amateur radio. I have gotten many comments regarding the pleasant and natural sounding nature of my audio. I could use a D-104 with this setup, but I have been using a Heil Classic mic through a basic W2IHY preamp.
My home-brew AM transmitter is standard amateur radio audio design using unbalanced audio input to a communication grade speech amp using a 6SJ7 mic amp, 6N7 phase inverter, and PP6A3 drivers to drive the 811A modulators. A special thank you goes out to K5UJ who took the time to tutor me on some of the finer points of broadcast audio theory. Since the previous thread has been closed for further replies, I thought I would start a new thread to say thank you if nothing else. I do understand that the essence of amateur radio is communication, and the essence of broadcast is commerce. A sincere thank you to everyone who answered my previous thread "how to get high fi audio".