Thursday 11 September 2014

A New 630m Loading Coil & Variometer

I've decided, for the time being, to keep my 2200m (136kHz) antenna tuning system separate from the 630m system. This means that I'll need to build a new loading coil, variometer and impedance matching transformer. I'm not really sure why I should maintain the 2200m capability since there is not really much activity here. The only two excuses that I have at present are the fact that it took a heck of a lot of work to get to this point (but it was mostly "fun work") and that the U.S. may be getting the band soon. I'm also not convinced that even if the U.S. does get the band that it would translate into much new, for the time being, I will keep the system intact.

I've used an online coil calculator to design the coils needed for loading and for the will be interesting to see how close the finished values compare with the calculated values. I hope they're not too far off! Here is what the plan calls for:

The main loading coil will be built on a low-loss 6" styrene pipe coupler using #16 solid copper transformer wire, spaced at 3mm. The coil will be elevated above the main form by strips of styrene rod that I have filed small notches into, every 3mm. The rod height will be staggered around the form, gradually stepping down one full turn every 360 degrees. Inside the main coil, the smaller variometer coil will be wound with poly-covered #18 stranded wire on a short length 3 1/2" PVC pipe.

Hopefully I'll get something that tunes from 130-230uH, approximately....if so, I'll not only be happy, but really surprised!

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