Ham Audio Spectrograms
Showing the different types of audio Hams are transmitting in the persuit of the best sound.
In an effort to illustrate the audio on the Ham bands today on a serious note, I have made spectrograms of the different types. I am using a Ten-Tec Pegasus transceiver and feeding the audio into my computer sound card. The analyzer program is a SpectraPLUS audio analyzer running in Windows 98. It is calibrated to the sound card and receiver. The Pegasus is uniquely suited to this since it is possible to listen to an SSB signal, at any bandwidth up to 8Kc wide, with an absolutely flat response. Except for the AM broadcast item, I collected all these spectrograms on 17M over a period of two days.
This is normal SSB audio as produced with the hand mic that came with the radio. It is clear "communications" audio. It begins at 300cps and extends to 2.9kc (a bandwidth of 2.6kc). It is reasonably flat in response and sounds very good and clear. It is easy to tune and copy "in the noise". The small bump from 3kc to 3.5kc is band noise coming through my filter, which was set at 3.5kc. This shows that the signal was about 20dB above the noise. Strong signals, say 20 over, won't have this artifact.
Here we have superb audio that sounds very robust and brilliant. Hams would call it "broadcast quality". It starts at 110cps and goes to 3.1kc with a 2.990kc band width. It, like the audio in Fig 1, would be effective even with weak copy, since all the audio falls within a 10dB range and has it's energy over the whole bandwidth. The factor that gives it's "broadcast" nature is the 110cps bottom.
This is an AM broadcast radio newscast received in SSB mode. It sounds very good...broadcast quality. It is well equalized and begins at abt. 60cps. You would think this would be the goal of the serious audiophiles.
This is a typical audio tail chaser with a rack of audio gear and a $1000 microphone. His audio begins at 50cps and ends at 3.5kc., I guess. There is a difference of 40dB between his high frequency and his low. Needless to say it sounds very bassy and mushy. It is also difficult to tune and clarify. Changes in tuning of 1cps has an effect. He thinks it is great, and while I was making the trace, some breaker encouraged him by saying his audio was excellent. He is putting most of his RF energy into the bass which contains little or no voice intelligence. If he was a S6 or S7 signal, instead of 25 over, all the intelligibility in his transmission would be in the noise and he would not be copied. I'd give him an RST 1 9 1. To refresh your memory, R=readability, S=strength, T=tone(clarity for SSB).
Here is a Ham with a good mic and a new W2IHY box. His friends have helped him adjust it on the air. He thinks it is great. It sounds boomy and a little strange. The holes in his spectrum are obvious at 800, 1,600, 2,400, and 3,200 cycles. These are the exact frequencies on the sliders on the IHY box.
I think the best sounding audio begins at 100 to 150cps. Audio much below 100cps doesn't help the "broadcast" quality sound desired, and it makes the signal hard to tune. The weak signal readability is also vastly complicated. There are some Hams using doctored radios with a 6kc bandwidth. This is not only illegal, but very selfish. It's like parking your car sideways using two places in a crowded mall lot. Further more, most radios can't hear all the audio through their passbands anyway. Most of the best sounding stations that I have ever heard use no more that a 2.8kc bandwidth.