[GreenKeys] Wobbly FSK ?

[Duncan Brown]

I had never heard of "wobbled" FSK either, but I would have to agree 
with Richard, It would tend to spread out the FSK'ed Mark & Space tones 
slightly, which could make the signal less susceptible to selective fading.

I looked in some of the AWA's old manuals and found that in the 
"Frequency Shift Keyer, Navy Model FSA" (Navships 900,754; 15 Oct 1945) 
there is a wobble control with a description identical to the one Nick 
gave.  (Maybe  the FSA was an earlier versionof the KY-30?  Freq. range 
is the same, though front panels are different.)

Have fun,

Duncan
K2OEQ


On 02-Aug-11 17:35, Richard Knoppow wrote:
> I guess that there is a technical paper on this burried away 
> somewhere. I think the idea is to broaden out each mark and space 
> pulse so as to make it less likely it will be completely lost by 
> selective fading. As I am sure you know selective fading results when 
> a signal is received via two paths of nearly the same length so that 
> they cause a comb filter effect at the receiver nulling out some 
> frequency. Usually, the path lengths are not very stable so the exact 
> frequency of null moves around plus one or both signals may have 
> regular fading, that is a change in stength over a wide band. By phase 
> modulating the pulse at a fairly high rate, fast, that is, in 
> comparison to its duration, the spectum is widened somewhat which 
> makes it less likely the entire signal will be lost in a null. It is, 
> in effect, a sort of frequency diversity. I have no idea of how well 
> this works. I have only the vaguest memory of reading something about 
> the theory long ago. BTW, I fell into your web site last night, what 
> an amazing collection of material:-) -- Richard Knoppow Los Angeles 
> WB6KBL dickburk at ix.netcom.com