[Elecraft] K3 and Quadra amp automatic bandswitching SUCCESS

[Jerry Flanders]

For anyone struggling to get their Yaesu Quadra amp interfaced to the K3 -

1. In it's original condition, the K3 provides no means to pull up 
the band data lines.

2. In it's original condition, the Quadra provides no means to pull 
up the band data lines.

3. The Quadra has 10K resistors wired from each band data line to 
ground, pulling DOWN any voltage impressed on the band data inputs.

4. The Quadra uses a 74HC244 device to interface the band data lines 
to the outside world, which requires around 3.5 volts to switch to 
the high state.

For band data line HI/LO switching to occur, you need to provide your 
own pullups of the appropriate size to provide enough current to deal 
with the 10K "pulldown" resistors inside the Quadra and still bring 
the band data lines up to around 3.5 Volts.

I tried 10K pullup resistors before I did the math, which failed 
because not enough current could flow to bring the lines up to the 
3.5 V minimum. I am now using 2.2K resistors connected to a +5V 
regulator and now I have all lines switching properly, and the Quadra 
will now follow the K3 with automatic bandswitching throughout the 
entire 160 - 6 M range. I have separate cables made up for each of 
the two independent inputs and either works properly now (only one is 
required).

I will try to wire up the remaining lines tomorrow - ALC, ON/OFF, 
PTT, TX INH etc.

I received the DB15HD breakout board I ordered ( 
http://www.winfordeng.com/products/brk15hd.php ) and have made up a 
new cable with it.  That breakout board gives enough space for 
everything needed, including the FSK and ALC connections. It also has 
screw terminals, which makes it easy to patch it all together.

The board is wider than I have clear space for at the back of the K3, 
but it works OK if I  plug the DB9 in last.

This board looks like a good solution to the problem of connecting up 
to all those pins in the DB15HD but is a little pricey at $16 + 5.50 
shipping. Adding a DB15HD male to female extension cord (which the 
same company also sells) would simplify things and make it possible 
to put the breakout board in an external box.

Jerry W4UK