Monty,
Perhaps I didn't explain my thinking it too well.
Apparently the normal K3 FSK implementation has both frequency shift and
amplitude shifts. The time domain plots show an amplitude change from
mark to space. The frequency domain plots show the frequency shift
which is FSK keying. Both modulate the "carrier" and generate sidebands
which widen the signal.
The time domain pix show a power level change between mark and space.
In the case of the standard K3 those transitions are sharp. In the case
of the reduced bandwidth FSK, there transition is almost a straight
line. The slower transition has to generate lower level sidebands.
For an analogy:
Take the case of a pure CW wave, it is a very narrow bandwidth signal.
Key off and on at 40 wpm and the sidebands arise. Use Elecraft's raised
cosine to smooth the zero to full power transition and the bandwidth is
narrower and sidebands close by are much reduced.
Given the above, I stand by my conclusion that if the mark and space
powers are equalized, the sidebands close in could be reduced. How much
is the question. One qualification is not knowing what the improvement
provided is. (One could in theory imagine the a brick wall filter
around the primary signal. Then it wouldn't matter what caused the
sidebands. )
73 de Brian/K3KO
On 3/25/2013 22:39, MontyS wrote:
No transition sounds like a square corner to me, generating all kinds of
square wave interference.
Monty K2DLJ
-----Original Message----- From: Brian Alsop
Sent: Monday, March 25, 2013 5:56 PM
Cc: ElecraftReflector
Subject: Re: [Elecraft] [Elecraft_K3] A Different View--K3
Reduced-bandwidth RTTY Analysis
Interesting. At at least the transition between the mark and space
amplitudes are smoothed some. I wonder how many db in spectrum purity
that buys. If it buys something, imagine what no transition would buy.
73 de Brian/K3KO
On 3/25/2013 21:11, Hank Garretson wrote:
On Mon, Mar 25, 2013 at 8:27 PM, Brian Alsop <[email protected]
<mailto:[email protected]>> wrote:
I notice that in the narrower signal spectrun the two tone peaks
have the same amplitude.
Many of us have wondered why our watt meters diddled like the RTTY
tones.
Hopefully that is fixed too.
Not fixed. See the before and after photos.
https://picasaweb.google.com/StarrGarretson/2013_03_25_K3_FSK
Which brings up one of my crotchets.
One of the most useful and important station accessories is an
oscilloscope. Much more useful than one of those multi-hundred dollar
watt meters--who cares if it is 150 or 153 watts?
An oscilloscope centered before your eyes can instantly tell you a whole
bunch about your signal.
Is your keying too hard? Are you overmodulating? Are you
overcompressing? Are your RTTY mark and space different in amplitude? Is
your amplifier adjusted correctly? Do you have the right antenna for the
right band selected? Has something gone wrong with your antenna? Do you
have hum on your signal? Etcetera.
If more hams had a monitor scope, we wouldn't have so many rotten
signals on the air.
73,
Hank, W6SX
Mammoth Lakes, California
Elevation 8083 feet in John Muir's Range of Light
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