ozQRP MDT, Construction Manual

Page: 38 / 42

MDT Construction Manual – Issue 2 Page 38
11.5 M
ARKING THE
VFO
SCALE
The VFO dial on the front panel comes without any markings. The reason for this is that the
frequency range will be slightly different for each kit due to variations in component values and
the selected frequency range etc. There are many ways to mark the scale, but following is an
easy and simple method:

Ensure the MDT has been powered on for at least 10 minutes to allow the VFO section to
warm up and stabilize. This is especially important if any of the VFO components have
been recently soldered.

Connect a frequency counter across R8.

Rotate the Tune control fully anti-clockwise. Read and note the frequency on the
counter.

Rotate the Tune control fully clockwise. Read and note the frequency on the counter.

From the two readings determine what markings you wish to make on the scale. Marks
at every 10KHz would be a convenient option.

Start at the low frequency end of the tuning range and while monitoring the counter
rotate the Tune control until you reach a 10KHz point. For example 7.060MHz.

Make a mark on the scale at the knob pointer line. A fine point felt marker is ideal.

Rotate the Tune control until you reach the next 10KHz point. For example 7.070MHz
and make a mark.
 Repeat the process across the tuning range.