The construction and alignment
of the DB6NT transverter is adequately described in the construction
manual. DB6NT says you can do the alignment with the minimum of
test gear and tools ...a +12V DC supply with 0.6A current limiting,
an analogue test meter set to the 0-10V DC range and a dummy load.
In practice I also found
it useful to listen for the crystal oscillator on its fundamental
frequency... my IC706Mk2 easily found it, on 135.667MHz. I could
also check it more accurately with my Racal Dina frequency counter,
but the IC706 at least was a quick and easy way to verify that the
circuit was working!
DB6NT provides four test
points for alignment. Aim to tune the bandpass filters for the voltages
(at the frequencies stated) as shown in the manual. I found these
voltages, when adjusted for optimum output, to be a little different
to the book but my other test gear, in particular my HP spectrum
analyser, was much more use than the voltmeter method as I could
then easily tune each stage for optimum output consistent with lowest
amplitude of spurious signals. If you have a spectrum analyser then
When the module was finally
adjusted I got a healthy 260 milliwatts output at 3.4GHz. This was
later reduced by means of an attenuator to drive the 15 watt PA.
However the "barefoot" transverter would still make some
interesting contacts with just the quarter watt of RF output.
When adjusting the receiver
cavity (pillbox) resonator be sure to set the tuning screw to the
first position where there is a noise peak... there is a second
peak when the screw is turned further into the filter. Do not chose
this one ... the first peak, ie with the adjustment screw furthest
out, is correct. I then listened for a marker signal generated by
my Adret synthesiser and diode multiplier, set to produce a signal
on 3400.100MHz. I could not miss it... it "pinned" the
S meter on the IC202S IF transceiver which I use with my all transverters!
A method of generating accurate marker signals in the amateur microwave
bands is a most useful "tool" and is highly recommended.
You can find more information on this
and other test gear elsewhere on this website.
The transverter may be
used "barefoot", without any more amplification. If you
decide on this then you need only mount it and the microwave coaxial
relay in a suitable box (an diecast aluminium box for example).
In my case I decided to add a high power RF amplifier on the transmit
side. This required a much bigger enclosure being made! The next
section shows you how this was done.