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 activity....so, 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 variometer....it 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!

Steve McDonald, VE7SL, is a regular contributor to AmateurRadio.com and writes from British Columbia, Canada. Contact him at [email protected].

6 Responses to “A New 630m Loading Coil & Variometer”

  • Hans (BX2ABT):

    I am still busy with my variometer, but last year I already found out that I couldn’t get the inductance I wanted. I am considering to use double/pyramid winding this time (http://www.strobbe.eu/on7yd/136ant/#VertRes). For wire I use old UTP/Cat5 cable. It is rather thin and could break, but I use two strands twisted together.

    But why the stand-offs for the outer coil? Would you care to explain? Cheers. –Hans

  • Steve VE7SL:

    Hans….how much inductance did you need? The reason for the standoffs is to put as much wire in the air without making contact to the form, even though it is low loss. Every little bit adds-up.

    Steve

  • Hans (BX2ABT):

    Unlike you I am bad at keeping notes in a tidy manner, so I can’t find them right now. But I know it was less than I wanted/needed.

    Those stand-offs look like hot glue sticks. I think I’ll first stick with the bucket as a form, maybe later I can try something to heighten the coil.

  • Hans (BX2ABT):

    BTW, I use this website for calculating the inductances.

    http://www.qsl.net/in3otd/variodes.html

    My current inner inductor measures around 450 uH and the calculated outer inductor aroun 1100 uH, which would give a range of 1088 to 1966 uH. Hopefully enough for a good start.

  • Steve VE7SL:

    Yes….the plastic buckets work fine. My coil was fairly small and I’ve had these styrene couplers here for several years gathering dust. I bought them originally for a DX crystal radio tuner and may still use them for that. I have seen that variometer calculator but have not used it . Are you building for 630m or 2200m ) Hans?

  • Hans (BX2ABT):

    We don’t have a 630m allocation here, yet, and I am actually surprised we have 2200m at all. So…still trying to be the first on 2200m from Taiwan, hi hi.

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