[Elecraft] [K3] K3 FSK power transients

[Joe Subich, W4TV]

> If you use the 
> standard 2125 Hz / 2295 Hz mark/space convention, this would make the 
> signal appear fairly close to the filter's transition band, assuming 
> there's no center frequency offset applied in the transmit path.

The roofing filter IS offset to put the RTTY tones (Data | Pitch) 
in the center of the filter.  However, since the 5 pole filter 
has +/- 1 dB of ripple in the passband and the ALC is applied in 
DSP (not based on power output), it is possible to see 20 or 30 
watts difference between the tones.

73, 

   ... Joe, W4TV 
 



> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Randy Farmer
> Sent: Sunday, September 27, 2009 4:33 PM
> To: Phil NA4M; elecraft at mailman.qth.net
> Subject: Re: [Elecraft] [K3] K3 FSK power transients
> 
> 
> 
> >I experience the same issue and Elecraft indicated that the FSK 
> >mark/space power fluctuations are caused by the transmit filter's 
> >passband ripple and where the transmit signal falls within 
> the filter's 
> >passband.  I'm using the standard 5 pole 2.7khz filter.  
> They indicated 
> >the 8 pole filter should be flatter.
> 
> I'm using a 2.8kHz 8-pole as the main transmit filter and at nominal 
> 100W output I can see a perceptible "wobble" on the wattmeter as the 
> signal shifts between mark and space. It's hard to believe the 
> ripples in the filter would be so steep that a 170 Hz difference in 
> frequency of the two tones would make much difference. If you use the 
> standard 2125 Hz / 2295 Hz mark/space convention, this would make the 
> signal appear fairly close to the filter's transition band, assuming 
> there's no center frequency offset applied in the transmit path. This 
> amplitude mismatch will introduce an  unintentional AM at the baud 
> rate, but it's probably not enough to appreciably broaden the 
> transmitted signal. I don't have access to a spectrum analyzer or I 
> would examine this further. Maybe someone with a well-instrumented 
> bench can have a look and report back.
> 
> 73...
> Randy, W8FN 
> 
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