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

Fri Sep 12 19:05:00 2003

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.

If +/- 1000 Hz isn't enough to show the curve, then the signal needs a
lot of help, even if you might quibble on whether the +/- 250 Hz
intercept is really -31 instead of -33.

If you say that your goal is to have the +/- 250 Hz intercept points
on the curve down 55 or 60 db, when you get it that good, showing it
with a RX bandwidth of 2.1 or 2.8 KHz won't change anything, unless
you're trying to see how far out -90 db is.

If the clicks are +/- 1500 Hz, a 2.1 KHz filter will make it look
BETTER than it really is.

I'll take your option three, or as close as I can get.

Guy.

AB9GV wrote:

The moral of the story:  Yes, dots per second changes the amount of
power in the clicks, but it doesn't
change the peak power in the clicks.  The apparent peak power in the
clicks depends on the bandwidth
of the filter being used to measure the power.

Narrow filters = long sample time = average power = clicks go away.

Wide filters = short sample time = more of the peak power = clicks get
bigger.

Really wide filter = shorter sampling time than the click = all of the
peak power = big as it gets.

I guess this means that there is a perfect receive bandwidth to make a
given rig's clicks look their
worst compared to another's.

On our ears?  Double the width of the filter doesn't increase the
amount of signal, but it does double
the amount of thermal noise, and it should re-double the amount of
click, up to the point.

73, de Michael AB9GV

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