Barry OGrady wrote:
I recently obtained a Yaesu FTDX-400. I have operation and
service manuals but I can't find how to add bands.

Just looking over the manual for a minute, it looks like the band switch
selects one of eight crystal positions, and that output is beat with the
VFO and the modulated signal to form the output.

According to the manual, all eight positions are filled, and there are three
empty positions at the end. It looks like the trimmers are all in place if
the manual is any judge.

So, it looks to me like if you want to add bands, you would first need to
fill those three positions and set the trimmers.

The bandswitch also switches several other stages. You'll notice the last
three positions of S1e, S1f, and S1g are disconnected and you will have to
connect those to the appropriate points on the filter networks for the bands
you are using. But I suspect nothing would have to be added other than
jumpers.

It would be an interesting exercise.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."