3.4GHz Transverter - page 3

Alignment of basic transverter


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 use it!

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.