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

Fri Sep 12 22:39:00 2003

What we did with the wide SSB RX filter was to try and take the
receiver OUT OF PLAY. For moderate cases we succeeded quite accurately
at handing the problem uncluttered to Spectrogram. From there on it's
just math in a CPU.

Your question, or argument, at this point deals with whether
Spectrogram can do what it advertises.

By listening through a receiver you have converted the signal to be
examined into a fairly faithful audio parallel to the RF. If the
received audio sounds clean, full range and undistorted to your ear,
it's likely close enough. (Note here that limiters, signal processing,
etc can add distortion/change not present at the RX input, and all
such should be off.)

It's a frequency shift to a range for which you have a convenient
analog to digital conversion device:

...your sound card, which converts that analog to digital, which
Spectrogram processes. The program's doing it's own thing. The narrow
resolution possible simply means that any odd artifacts to the
received signal will likely be presented quite clearly and faithfully.
The MP has some interesting artifacts.

I would have killed to have a setup like this back in the 60's when I
was working AT&T long distance plant.

Just about everything I had back then (including some really pricey
multi-multi-K$ analog stuff) is rendered obsolete and fairly crude by
a modern SSB RX, PC sound card and Spectrogram.

We are living in a wonderful time for techno-tinkerers.

73, Guy.

----- Original Message ----- 
From: "Masleid, Michael A." <[email protected]>
To: "Guy Olinger, K2AV" <[email protected]>
Cc: <[email protected]>
Sent: Friday, September 12, 2003 8:00 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