linrad support: Aluminium thickness and magnetic pick up
(April 13 2002)
The 2.5MHz to audio converter was placed 15cm above a transformer with a large leakage field (transformer for a desoldering station) The transformer was placed and oriented for maximum interference pick up. Fig. 1 shows the screen without any box for the 2.5MHz to audio converter. 
freq   level
(Hz)    (dB)
 50      42
100      17
150      44
200      13
250      38

Fig.1. No screening.
Fig. 2 shows the screen with the board mounted on 1mm aluminium while fig. 3 shows the screening with 3mm thickness for the box aluminium. Fig. 4 shows the screen when the transformer is switched off. There are several other transformers within 2 meter distance from the unit but they do not produce strong enough magnetic fields to give any visible spurs. The screen is only below the board and some weak 2.5MHz signals are picked up.

Fig.2. Screening with 1mm aluminium.

Fig.3. Screening with 3mm aluminium.

Fig.4. Transformer switched off.