[TenTec] Enhanced SSB

Fri Apr 18 22:49:31 EDT 2003

Paul,

I've been following very closely the digital experiments at WOR. For the rest of the folks: WOR is an AM radio station in New York. The most recent audio samples of the WOR analog and digital signals are most interesting: by that I mean the audio from the digital signal still leaves much to be desired. Maybe someday it will equal the 'old-fashioned' analog sound, but it just isn't there yet, and a comment to that effect has been made on the WOR web site by the engineers themselves. Yet, WOR will continue to transmit digital AM and soon everyone will be. Sometimes I think that hearing the word 'digital' gives people a warm and cozy feeling because it's new! it's digital! and so it must be better!

Yet, the RF pollution of the noise-like IBOC digital signal is awful. In the next few years, all of us AM DXers are about to be greeted by a  wall of digital noise that is soon to fill the airwaves. It will mean the end of AM Dxing as we know it. This is progress? This is better than a wide-bandwidth analog audio signal? Yecch.

Back on the topic that started this whole thread... I've noticed that the mere mention of 'enhanced SSB' or 'hi-fi SSB' or 'hi-fi audio' or '14.178' conjures up in people's minds a signal that is 6 kHz wide (or more!) and, thus, poor operating practice worthy, evidently, of action by the FCC itself to stop such operation. This topic, suprisingly, always gets a really emotional response on the bands, on the reflector, because for some reason, many hams begrudge the efforts of a growing number of hams to produce good audio within the limits of both Part 97 and good engineering practice.

One of the first and only things many people think of when they hear these terms is ultra-wide bandwidth. They assume that all you have to do to get a 'hi-fi' signal is to use a transmitter that passes frequencies far above 3 kHz. While this might help, it is by no means the only requirement or the only way to get a good, clean signal on the air.

There is plenty to be done to your audio even if you stay within the 3 kHz limit that is either spelled out or implied in Part 97.

Microphones, preamps, compressors, limiters, noise gates, parametric equalizers, graphic equalizers, filters, de-essers, processors, and,
yes, wider bandwidth filters, are all things currently employed by the big boys on, for example, 14.178.

I have heard remarkably good audio from guys with just 2.8 kHz wide filters in their transmitters. I think part of this is because I sub-conciously compare these signals to the average signal produced by a typical transceiver operated by ham who has never verified the settings of his mic gain, equalization and speech processor by actually listening to his own signal on a second receiver. The typical ham signal is typically horrible. The hi-fi guys, in contrast, are endlessly recording themselves, e-mailing the recordings to each other, listening to themselves, and tweaking everything for the best possible signal. Again, I must stress that there is a lot to do besides just widening your signal and thus inflaming the sensibilities of other hams. A clean, distortionless signal, even if it's only 3 kHz wide, sounds clean, distortionless, and awesome.

To be fair, there are some guys who have special 5- or 6- kHz wide crystal filters manufactured for their (SSB) radios, at great expense I
might add. In my opinion, this is borderline obsession and bending the spirit of Part 97 beyond reason. I recently had a conversation with a major crystal filter manufacturer who told me, "You'd be amazed at what some guys ask for." These guys are probably a minority of 'hi-fi' buffs, however. Please feel free to correct me if I'm wrong here.

A few years ago I installed high quality 2.8 kHz crystal filters in my radio so I could hear what the fuss was all about and so that I could receive more "hi-fi" audio from these guys. And since then I purchased a receiver with even wider bandwidth. The received audio is very good on 3 kHz-wide transmitted signals. I said this once before on one of the newsgroups and was laughed off of the thread by folks who told me I was crazy. Well, I am a weekend musician and frequently engineer my own recording sessions, so I am at least as qualified as the next guy to offer a reasonable opinion on the matter.

Here's an experiment anyone can conduct at home: Next time you're on the phone and making multiple phone calls, listen really closely to the audio quality of the persons on the other end. Over time, you're going to hear both really clean, crisp, noise-free signals and really crappy, mushy, and distorted signals. How come? Isn't everybody restricted to the 3 kHz bandwidth of the phone company? Shouldn't everyone sound equally bad? No. And the same goes for hams.

I recently had an e-mail exchange with a nation-wide AM radio talk show host in which he told me that he always announces when his callers are calling from a cell phone, "To explain the lousy clarity," he told me. Even to this guy, there is a difference. (See my comments about WOR above.) 

Someone suggested listening on 14.178 kHz for a few weeks to get an idea of what is being done in this arena. I would add that listening with a spectrum analyzer, so that you have some hard data, is even better. That's a pretty good suggestion and is required homework before weighing in on one side or the other of this debate.

Regards,

Al W6LX

> -----Original Message-----
> From: Paul Christensen, Esq. [mailto:w9ac at arrl.net] 
> Sent: Friday, 18 April 2003 12:16 PM
> To: geraldj at isunet.net; tentec at contesting.com; w8au at sssnet.com
> Subject: Re: [TenTec] Enhanced SSB
> 
> 
> > damping to let the microphone hear only the "golden tones" 
> of the ham
> > transmitting. AM broadcast doesn't even allow going to 15 KHz.
> 
> Prior to the implementation of NRSC mask in the early '90s, 
> AM Broadcast stations had no upper limit.  The NRSC mask now 
> effectively
> limits the audio passband to approximately 9.5 kHz....and the 
> service still sounds poor despite attempts by broadcast stations and
> receiver manufacturers to improve the quality.
> 
> WOR in New York has been experimenting (yes, even 
> broadcasters are allowed to experiment just like hams once 
> were) with digital IBOC
> but the jury is still out on whether it can be a viable mode 
> given sky wave propagation, fading, noise & interference, etc.  The
> IBOC receiver goes into an analog "blend" mode when the BER 
> reaches a pre-determined threshold.  I haven't heard it, but 
> I can only
> imagine...
> 
> -Paul, W9AC
> 
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