Perhaps another
hardware option: a recent QEX article from W6EAW mentioned the use of an
FE-5680A Rubidium source, which contains a programmable AD9830 DDS chip. A
number of these have become available second hand by several Chinese
sellers for around 70 - 100$. The " 1Hz-20MHz" (option 02) version has the
RS-232 serial interface brought to the external 9-pin connector, but
according to Matthias Bopp
this can also be retrofitted for the standard
fixed-10MHz version. I have ordered one of the programmable units, and when
it arrives I will attempt to generate LF and VLF signals directly from the
output.
Note that though Rb oscillators provide
excellent stability and reproducability (better than 1e-10), they
still need to be calibrated to achieve absolute frequency
accuracy.
Best 73,
Markus (DF6NM)
