Re: [RTTY] Distortion

[Kok Chen <chen@mac.com>]

On Aug 24, 2004, at 5:44 PM, Phil Duff NA4M wrote:

> I see no adjustment for FSK/AFSK drive level in RTTY mode to have no 
> ALC indication.

In "RTTY" mode, you are stuck at what the factory setting is.  The only 
front panel control that does anything on the FT-1000MP in RTTY mode is 
the power control.

In AFSK, I can get about 80-90 watts output from my 1000MP before any 
of the ALC bars start to appear.

In RTTY mode, some of the ALC bars are lit on my MP and I get 100 watts 
output max(which I can also get with AFSK by pushing the audio levels 
harder).

I should get off my lazy rear end and try to measure the difference 
between the distortion products with no ALC bar lit vs the distortion 
products with some of the ALC bars lit.

An RTTY signal has constant power and the two tones don't overlap so 
you can probably push the ALC quite a bit before you see much 
distortion product appearing.  With true FSK, you can even drive a 
class C amplifier. So the issue of how much ALC to use may be more 
important to PSK31 than RTTY.

At least on the FT-990 schematics that I have handy here (my MP 
schematics is a few hundred miles away :-), there is a pot labeled 
"RTTY Level" following the internal AFSK generator.  So presumably, you 
can adjust the Yaesu rigs for different ALC activity in RTTY mode.

73
Chen, W7AY
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