[AMRadio] AM Transmitter "quality"


D. Chester k4kyv at charter.net
Wed Sep 16 23:06:44 EDT 2009


 > I really don't care whether people chose to modify their old AM
> transmitters to "improve" sound quality, as they can do whatever they
> want with their radio. What does bother me a little is when people use
> words like "nasty" and "awful" to describe the audio quality of some
> classic transmitters, as if thedesigners of the day were not smart
> enough to design a decent transmitter.
>
> At the time these transmitters were built, the goal of amateur pone
> operation was effective radiotelephone service. Human speech falls into
> the range between 300 and 3000 Hz. There are sounds outside this range,
> but they do not contribute to intelligibility. So, in order to make the
> best use of the power available,  the bandwidth didn't need to be more
> than 4Khz.  The next logical step in the quest for efficient use of
> available power was SSB, which has an equally "nasty" sound but does the
> intended job quite well.

But, then, what's the point of running AM?  If all you are looking for is 
"efficient use of available power", why not just run space-shuttle quality 
SSB and be done with it?

It wasn't a matter of the designers of those rigs not being smart enough to 
design a decent sounding transmitter. Many of those stock "nasty" sounding 
rigs were designed with cost in mind, more than intelligibility or natural 
voice quality.  Others were trying to climb onto the "communications 
quality" bandwagon that became all the rage during that era, with the advent 
of SSB.  Many of the AM operators of that era were watering at the mouth to 
convert to SSB, but simply couldn't afford to buy the commercial equipment 
that was available at the time, and didn't have the technical know-how to 
build their own SSB rigs.

The original stock Collins KW-1 sounds pretty good.  Maybe not quite 
broadcast quality, but very good "amateur radio quality".  Later production 
runs were modified for "communications quality", and sound more like a phone 
patch from a land-line telephone using a carbon microphone.  Collins 
intentionally used under-sized coupling capacitors between stages, and 
by-pass capacitors to limit both high frequency and low frequency response. 
These later models sound more like an ART-13 or ARC-5 military transmitter 
than even classic "amateur radio quality" audio, let alone anything near 
broadcast quality.

I  helped Jay, W5JAY modify his late-model KW-1 back to the original Collins 
design, and the audio quality improvement was like night over day.

Don k4kyv

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