Dummy Load Construction
Introduction
Seeking an interlude from the Kingsdon project. I decide to build the Dummy Load, needed for transmitter testing !! I had thought this would be a quick job, indeed it should have been..
Construction
The resistors I had were 100 Ohm, I decided on a layout to give 50 Ohms and a max of 16 Watts which would be ample for my QRP projects. I trimmed the resistors then found this arrangement would not fit in the box I had already drilled for the PL259. Oh.. a rethink was required. I experimented a little and soldered the resistors in place. Unfortunately as the ends of the resistors had been trimmed right back (Long story) it was very hard to solder them together in the required configuration. Despite all this the dummy load seems to perform it's simple task..
Learning Points
- Check everything will fit in the box before committing to a layout.
- Don't bother trying to solder to an aluminum box! (It must have been late..)
- Use BNC connectors .
- The PL259 works loose.
- The physical layout is important as we don't want it shaking to bits and shorting!!
Conclusions
There will be a Mk 2
Dummy Load Mk 2
Mk I worked fine, but developed a rattle as a blob of solder came loose! Clearly this was less than ideal. Time for a rebuild with carbon resistors and a different layout. Now it is mechanically reliable, has a lower SWR from HF to 70cm's, plus the PL259 was replaced with a four nut fitting version, so it no longer works loose, the PL259 Socket with a single retaining nut is indeed, the work of the devil.