[Elecraft] Re: Displaying the keying waveshape on Spectrogram.

Fri Sep 12 21:59:01 2003

Michael, the effective FFT resolution used to construct the spectrum in
SpectroGram is unrelated to the bandwidth required to view the keyed
waveform spectrum. The smaller the FFT "bin" the more data points in the
plotted spectrum, but you have way more than enough without going to
extremes.

Guy is giving you the straight story . . .

Although, there is a counterpart method available to those who have
receivers with very narrow brick-wall digital filters in the IF. One uses
the narrowest filter setting and shifts in along on either side of the keyed
signal frequency and observes the S-meter. Those values are then plotted to
yield a very rough approximation of the actual spectrum.

I prefer using Guy's approach - it is much more convenient and accurate.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"Starting the 58th year and it just keeps getting better!"
[email protected]

----- Original Message ----- 
From: "Masleid, Michael A." <[email protected]>
To: "Guy Olinger, K2AV" <[email protected]>
Cc: <[email protected]>
Sent: Friday, September 12, 2003 7:00 PM
Subject: RE: [Elecraft] Re: Displaying the keying waveshape on Spectrogram.

Hello Guy,

>There is a point to using the widest possible SSB filter on the
>receiver feeding Spectrogram. First off, it helps to get the entire
>curve in one picture. Also once you exceed the +/- bandwidth of the
>"significant" click energy, further bandwidth does not change the
>curve anymore, and you get a reading independent of RX bandwidth.

>Practically speaking, being able to see up and down 1000 Hz will be
>more than enough to show a good or slightly bad signal quite
>accurately.

OK, true enough, to a point.  The SSB filter is being used as a band
pass filter.  The band pass filter should pass all of the signal
to make a measurement.  But, the curve is being made by Spectrogram.

The resolution (bandwidth) being used in Spectrogram is rather tiny.
Like 3 Hz?  That's the filter I'm worried about.  It needs to be wide
enough to capture the energy, say 500 Hz, 1000 Hz?

73, de Michael, AB9GV

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