[Elecraft] [Elecraft_K3] A Different View--K3 Reduced-bandwidth RTTY Analysis

[Brian Alsop]

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 <alsopb at nc.rr.com
>> <mailto:alsopb at nc.rr.com>> 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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>
>
>
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Checked by AVG - www.avg.com
Version: 2012.0.2240 / Virus Database: 2641/5703 - Release Date: 03/25/13