[AMRadio] AM Broadcast Quality


manualman at juno.com manualman at juno.com
Wed Dec 18 20:16:06 EST 2013


Although QEX probably has many more subscribers then Electric Radio, as
Rob points out, ER readers probably would be more appreciable of reading
your article and rolling the ideas into their AM equipment.

Pete, wa2cwa

On Wed, 18 Dec 2013 18:49:51 -0500 Jim Tonne <Tonne at Comcast.Net> writes:
> I have this awful feeling that some of the tube rigs that had 
> marginal 
> iron in
> the modulation path did so allegedly because "that's the way it's 
> supposed to be"
> but in fact the reason was cost-cutting.
> 
> If you use low-level speech processing (clipping, to be specific) 
> then 
> the low end
> must be as flat as you can get it.   It might be of interest to know 
> 
> that the shortwave
> broadcast transmitters (nowadays) themselves have a low-end response 
> 
> that goes
> down way below sub-audible.   The contract to the manufacturer 
> commonly says
> that the modulator must handle a 50 Hz sinusoid that has been 
> clipped 10 
> dB to
> have no more than 5% "tilt" in the output.   I know this because I 
> have 
> been
> involved with the design of those rigs (at Continental 
> Electronics).
> 
> This means that the low-end (bass) response must go down to way 
> below *one*
> Hz.
> 
> With those transmitters now using PWM, this is not a problem at 
> all.
> But with the Viking II and its bretheren it is a serious problem.
> 
> So, fellows, make the transmitter audio frequency response as flat 
> as 
> you can and
> then use a "speech processor" to shape the amplitude and frequency 
> responses.
> I am toying around with writing an article for QEX about how to do 
> this.
> 
> </soapbox>
> 
> - JimT W4ENE



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