[Elecraft] KX3 TX GAIN Values

[Virginia Greene]

My KX3 is almost five years old now.  Times sure flies, eh?

From the beginning, the output on 15M has been a little lower at maximum power setting than on the other 12 watt maximum output bands.  Typically, I’d see 9-10 watts.  No big deal.

More recently, I’ve been trying FT8 operation.

What I’ve observed is that for the first transmission on 15M using FT8, the output power starts out at 1 watt and gradually creeps up to perhaps 3 watts by the end of the transmission.  The next transmission might get to 5 watts, and the third might get to the final value of what I set - 7 to 12 watts.  (Yeah, I know about heating.  That’s not the issue.)

I think this is due to the way the ALC system works in the KX3.  It doesn’t exhibit this behavior on CW.

But, other bands are not nearly as bad.  For example, on 80M the maximum output is attained on FT8 within a second or so of the first transmission.  On 10M, it takes about three seconds.

This start-up thing happens every time I change bands.  That suggests that the ALC is slowly adjusting per band.  Makes sense.

In an attempt to correct this, I tried a TX GAIN calibration.  It didn’t help.

I asked the very helpful, and currently overwhelmed, support folks at Elecraft about this.  Doug sent me the factory original config file for this KX3 to me, asking me to try loading it and checking, thinking that perhaps some value gotten corrupted somehow.  That didn’t help, though it was a great idea.

So, I started looking through the TX GAIN values that you can view when the TECH MD menu entry is set to ON.  What I discovered was that the 15M value was and is significantly different than for the other bands.  This was true for both the factory original calibration as well as a recent TX GAIN calibration.

My guess, and it’s obviously a guess, is that the amount of ALC correction done on changing bands is somewhat related to the TX GAIN value.  So, the very different TX GAIN value for 15M is taking much longer for the ALC to adjust to than on the other bands.

My question of all of you is: What is the TX GAIN value for your KX3 on 15M?  

Perhaps what I’m observing is normal and just the way the radio works.  But, maybe, there’s something amiss with the hardware.  No way to tell without poking around inside with an oscilloscope, which I’d love to avoid if I could.

Thanks very much for any help.

Clarke  K1JX