[Elecraft] K4 on AM

[W2xj]

i would beg to differ. Amateur radio is a hobby comprised of experimenters, home-brewers, DXers, contesters, ragchewers, CW enthusiasts and EM comms to name a few. Each group has their own technical needs. 

Regarding AM in transceivers,  it hasn’t been properly implemented for the last 50 years or more. It is a derivative based on SSB generation which introduces many shortcomings with the worst being steep skirted SSB filters.

I’ve worked professionally with AM broadcast transmitters since 1958 and watched them evolve over the decades as we perfected the science over that time. I’ve worked with LW and MW transmitters to 2 megawatts and shortwave to 500 kilowatts over the years and consulted on design with almost every major TX manufacturer. 

One of the basics is that a transmitter should have an audio bandwidth 2 to 3 times the actual transmitted audio bandwidth. Bandwidth and peak control is then external to the TX. Lack of that capability is part of the reason some transceivers sound bad on AM. It is also the source of part of how some hold AM in low esteem due IM and other distortions in the linear amplification  chain, again, due to a predominately SSB oriented design. There are a number of modified BC TXs mostly on 160 and 80 meters with audio bandwidths between 10 and 20 KHz and they dont have the same issues but they do have proper audio processing feeding them.

Back in the 1950s when AM still ruled the ham bands transmitters did not have the same issues as they were designed for AM and CW operation and did not have audio filtering even though there were more hams back then. Spectral distribution of speech have frequencies around 5 KHz20 to 30 db below speech fundamentals so the impact is not what many might think when the TX is otherwise clean. 

Bottom line, AM in transceivers is a compromise that takes a back seat to SSB. 

Sent from my iPad

> On Mar 2, 2020, at 3:07 PM, Joe Subich, W4TV <lists at subich.com> wrote:
> 
> On 2020-03-02 11:34 AM, Grant Youngman wrote:
> >
> > A maximum around 6 KHz would be better,
> 
> Audio response greater than 3 KHz is *never* appropriate for
> amateur radio.  Amateur radio is, after all, a communications
> service not an entertainment medium.
> 
> As a certain FCC official said in a hamfest forum a few  years
> ago, "if you want more than 3 KHz, get a *BROADCAST* license."
> 
> 73,
> 
>   ... Joe, W4TV
> 
> 
>> On 2020-03-02 11:34 AM, Grant Youngman wrote:
>> An audio response of 4-5 KHz isn’t unreasonable.  A maximum around 6 KHz would be better, and since it will be adjustable, the response (with relatively steep rolloff) can be tailored to be compatible with band conditions and occupancy as necessary.
>> I know this is a sensitive, if not plain explosive, topic in some circles — but most AM users do manage their bandwidth with common sense, and to be considerate of the rest of the community.
>> Grant NQ5T
>>>> On Mar 2, 2020, at 10:46 AM, Eric Swartz <eric at elecraft.com> wrote:
>>> 
>>> One note - Wayne is saying the K4 -audio- b/w in AM will be somewhere
>>> between 4 and 5 kHz.  The actual DSB AM b/w that results will be between 8
>>> and 10 kHz.
>>> 
>>> 73,
>>> Eric
>>> *elecraft.com <http://elecraft.com>*
>>> 
>>> 
> 
> 
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