KAT2 (ATU) Alert #3: SSB ALC
Improvement with KAT2
29 March 2000
Applicability: KAT2 ATUs shipped prior to Mach 29, 2000
A few KAT2 builders have reported that transmitted SSB is not as clean once the auto-tuner is installed. It can be heard on a monitor receiver as a somewhat harsh attack characteristic on the first speech syllable.
We have determined that the cause of the problem is a small delay in ALC response caused by the ATU's SWR bridge. To cure the problem, C50 and C51 on the KAT2 control board must be replaced with smaller capacitors (the original value is .01 uF). This change is strongly recommended for anyone using the KAT2 with the SSB adapter. We apologize for the inconvenience.
All KAT2 kits shipped after March 29, 2000 will include this change.
You'll need two .001 uF capacitors (Radio Shack #272-126 will work). This is an extremely common value, and you can use virtually any type (ceramic disc, monolithic, mylar, mica, etc.). The value is not critical, so you can use capacitors with a 10% or 20% tolerance. In fact any value from 820 pF to 1200 pF can be used (.00082 to .0012 uF, or 0.82 to 1.0 nF). The voltage rating can be anything from 10 Volts up.
The two ATU boards must be separated to get at these capacitors. When you remove the old caps, be very careful not to damage any nearby traces, especially the fine trace that runs underneath C51.
No re-alignment is needed, assuming you don't change the settings of R1 and R2 during the modification.