Ham STAMPFL RF SHARK, Building Instructions

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TCXO 30MHz
DDS AD9851
FUNCTIONAL STATEMENT - RF SHARK
THE DIGITAL PART::
Processor
Output Transformer T1-1T
As in the previous JUNIOR 1D kit, an ATMEL processor takes over the control and LCD
display. The processor continuously emits high-frequency interference. These are to be
suppressed directly at the outputs using a fi
filter. The low-frequency components are
subsequently screened again using a low-pass fi filter.
An additional measure to suppress interference radiation is the ground area on the
underside of the board. The signal quality of the local oscillator is of the utmost importance
for a clean reception!
The quality is directly related to the clock frequency of the DDS.
A basic rule says: The maximum required output frequency should not be higher than 40 -
50% of the clock frequency. In RF SHARK it is 180 MHz obtained from a 30 MHz TCXO of
high accuracy that is multiplied 6 times. In RF SHARK, the ratio of DDS clock and
generated LO signal is always less than 23%..
f the DDS signal generated is also taken off symmetrically by means of an HF transformer,
the purity increases, because the interference signals contained can only cancel each
other out. After passing through the 40.7 MHz low pass fi
filter, the LO signal is ready to be
fed to the fi first mixer. A very big improvement is the optical quality encoder. The slightly
higher additional costs are defifinitely worth it! Not only is a long lifespan ensured, the zero-
play concentricity guarantees an excellent feeling of coordination.
The bands can be selected directly using the "Amateur" or "Radio" buttons. The LCD
display with 4 x 20 characters shows the start and end frequencies of the desired band.
All control signals and the supply voltage are fed to and returned from the analog section in
duplicate via plug contacts. In a nutshell, RF SHARK is a powerful, safe and easy-to-use
shortwave receiver.