Feb 20, 2006:
This is the interior of the SX-20. A pair of P3055E FET's, driven by
a single P3055E are used to make 10 Watts RF. They can be seen center
right with the large cooling blocks. The receiver frontend is a NE602
and the IF uses a six-pole ladder filter, seen center-top of the image.
A few ideas came up after opening the case: 1. The schematics came with a couple of Ramsey mods which improves selectivity.
2. RF-power can be regulated by adding an external ALC potentiometer.
3. The large connector under the flatcable can hold an audio CW filter. The idea is to have this filter switched from the front panel using the MODE switch.
The rig comes with a Digital VFO which operates around 8 Mhz, which gives me an IF frequency of around 6 MHz. However, the rf diagram (523 k) doesn't give any values for the crystals in the ladder filter.
