Saturday, November 17, 2012

New box for the noise-bridge

Decided to separate the noise and the bridge for convenience.

Here's the new box for the noise generator, again an old if transformer can:


I could had placed the battery inside but would be a little crammed and difficult to change so a small patch was made:

For the bridge itself, I had no small (in size) variable cap to put inside so improvised with an polivaricon and the shaft of a defunct pot

 Some grinding was needed for the rotating knob of the polivaricon (it was from a pound shop radio).
Some "Araldite" glue after...
 ....allmost perfect

 And here's the the bridge. Scale is to be finished, I only placed the 50 Ohm mark and the 68p "unknown" internal cap (close to half the varicon) on the reactance side:

 Main capacitor is of 146pF and I had no more bnc plugs so used a cable for the "rx" part.

Inside, lot's of space left if chose latter on to put an internal noise source.
 In practice it's preferable to use the MFJ analyser but you learn a little more building your own test equipment and can always cross-check the measurement made.

Preliminary tests made to my dipole have the same result as on the MFJ equipment.

Have a nice weekend.


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