Re: [Amps] IMD

["Gary Schafer" <garyschafer@comcast.net>]

Hi Bill,

This is not a problem of not producing the square wave itself. 
A perfect square wave has all of the odd harmonics in phase. 
When you modulate an SSB transmitter with a square wave the phase of the
fundamental and harmonics shift. This produces another fundamental that sums
together.

To pass an ideal square wave signal in an SSB transmitter requires infinite
bandwidth and infinite amplitude. Though the square wave is not the ideal
one it still requires a high amplitude capability.

This is pointed out in the Collins "fundamentals of SSB".
Here is a link to an article on the subject by Wes Stuart N7WS.

73
Gary  K4FMX

> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Fuqua, Bill L
> Sent: Friday, January 06, 2012 2:17 AM
> Cc: amps@contesting.com
> Subject: Re: [Amps] IMD
> 
>   The spikes at the beginning and ends of a square wave are produced
> when higher frequency harmonics are removed such as by using
> a low pass filter. And their amplitudes are  limited to only about 9%.
> That is because the harmonics amplitude drop of as 1/N where N is the
> harmonic
> number. This is why I said "Google Fourier  Gibbs phenomenon." To have a
> perfect square wave all the odd harmonics must
> exist at the right amplitudes.
>    It is true that a perfect ideal square wave will produce infinite odd
> harmonics but they drop in amplitude very quickly.
> 
> ________________________________________
> 
> "The leading and trailing edge portions of the square
> wave stack up and create an infinite amplitude at each."
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