On Thu, 24 Jul 2014, 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.

Well there are no diodes to clip on that baby, if that's what
you're asking.

You'll have to take out the bandswitch, put in a new one with more
positions, then add any needed coils and crystals for the new bands.

I'm assuming there is a crystal for each band, perhaps it's like the
Swan rigs where the bandswitch changed the VFO tuned circuit.

Of course, nobody is going to rip out the bandswitch.

So adding bands means changing the crystals (again assuming there are
crystals), swapping an existing band for a new band, or manually changing
crystals when you want to change band. If you're lucky, the tuned
circuits will cover more than the current bands, the moreso as you go up
in frequency. But if they can't cover the new bands, you'll have to
switch in some coils in parallel, to lower inductance if you want to move
the tuned circuits up in frequency, or add capacitance in parallel with
the tuned circuits to lower them in frequency. Maybe acceptable for adding
one band, too much trouble otherwise.

This rig dates from 1967. The bands had been more or less stable for some
time (well 11 metres was lost in the US and mostly lost in Canada in the
late fifties). That only changed in 1979 when the original WARC bands
were added. Some rigs did have auxiliary band positions, so you could
accomdate a new band. But for the most part, the old rigs stayed on the
old bands, while new rigs came along (now 35 years old) that could
accomodate the new bands. My TS-830 covers the WARC bands, it came out
just at the right time. But something a bit earlier likely lacked the
capability.

Then shortly after the WARC bands came into use, the rigs started
changing, no crystal for each band, it was all synthesized so the
potential for broader tuning was there. That's where the "clip
the diode" notion comes from, later rigs that could tune wider, but
had restricted tuning as they came from the factory. After a bit,
every new rig had a general coverage receiver, any control over
frequency coverage was about transmitting.

Michael