Peter, G3LDO mentioned his difficulties to build a reliable and stabile
exciter for LF and describes the solution developed by DJ1ZB.
I myself also had my difficulties to build a solution from scratch. After
experimenting with 5-6 MHz VFOs and frequency dividers, I came accross a
nice synthesizer kit. With a frequency range between 1 Hz (!) and 54 MHz
(!) it is a real overkill for the LF band, but the features contained in it
are excellent for what we are doing. The resolution is 1 Hz, the accuracy,
once calibrated is in the same range and long time stability is excellent