[Yaesu] FT-101zd question

[Dr. Gerald N. Johnson]

That was written in Japanese by a tech writer who didn't understand 
radio transmitter tuning and then transliterated into broken English by 
a technically illiterate translator.

Driving and loading are separate operations. You drive to make power, 
but if you overdrive you splatter. You tune and load to resonate the 
output PI network so it presents a resistive impedance to the PA tubes 
that is the impedance where the PA tubes give the greatest power output 
and are still operating in a linear mode. With only metering for PA 
plate current its conventional to drive for rated plate current, then to 
increase the loading in increments while tuning the tuning for the plate 
current dip. Typically one starts with the loading capacitor at some 
value larger than gives the proper load. This works best for class C 
which is NOT linear. Tuning a linear amplifier, I think, works best with 
a RF power output meter and tuning for maximum output power. The with 
voice adjusting the drive for occasional ALC indication. That presumes 
that the ALC threshold is set to properly prevent driving to clipping in 
the PA and the associated splatter. Otherwise an oscilloscope with 
adequate bandwidth to see the RF envelope is a good tool for setting the 
drive to prevent clipping.

73, Jerry, K0CQ

On 2/4/2012 8:37 AM, rb wrote:
> In the FT 101zd manual, page 14, I see this instruction:
>
> "Again rotate the LOADING control and PLATE control, each time advancing the
> DRIVE control approximately 2 step, until the DRIVE control is fully
> counterclockwise. The transmitter is now tuned for maximum power output. Do
> not exceed the maximum tuning time stipulated previously. Return the VOX GAIN
> switch to the VOX position (out of the MOX position, return the METER switch to
> IC, and return the DRIVE control to the fully counterclockwise position."
>
> This is a different process than I normally go through. What I do is set DRIVE
> to 150-175ma, and keep it there. Different things I do cause it to go up or
> down slightly. I just re-tweak it to wherever the plate currrent is I want to
> be at. I just switch over to USP/LSB from CW tune, leaving it right there.
>
> Going by the above process, it looks like you could easily get "over-drive"
> (loaded more than you'd like) by going to full clockwise. Than, going back to
> full counterclockwise seems you'd have zero-drive.
>
> I'd certainly like to know if this is the correct tuning.
>
> What keeps is from going into "over-drive", and what would make it be zero-drive
> if at fully counterclockwise position?
>