[RTTY] RTTY AMPLIFIER QUESTION..

[W6SX Hank Garretson]

At 09:00 PM 16 03 2009, Jack West, W7LD wrote:

>I have been wondering about operating HF Amplifiers in RTTY mode.
>It seems logical to me that when I run FSK it should be OK to operate
>my amp in "CLASS C" vice a linear class of CLASS B or AB2.
>
>My thinking is this:  In FSK it is essentially a CW signal operating on
>two separate CW frerquencies, alternating, with a seperation of 170 hz.
>Thus, it is OK to run my amp in maximum efficiency in Class C.

Yes, as far as your amplifier is concerned, it is a CW signal.  Shoot 
in the old days, CW signals with more than 170 kc of chirp were not uncommon!

>In the case of AFSK, it seems to me since the signal is generated by
>audio tones, the amplifer needs to be operated in a linear fashion as
>you would with any other sound card generated mode.

No, a properly generated AFSK signal is also essentially a CW 
signal.  Assuming properly adjusted sound card and transceiver, AFSK 
and an FSK are the same.  Properly adjust sound card and transceiver 
and run Class C if you want.

>So am I right?  Can I get more horsepower out of my amp by running
>it in Class C in FSK RTTY and not worrying about linearity?

More horsepower?  Yes.  How much more is another question.  Using 
ballpark efficiencies of say 75% versus 60% gives about 1 dB of horsepower.


73,

Hank, W6SX

Mammoth Lakes, California

Elevation 8083 feet in John Muir's Range of Light