Posted by: m1paf | April 20, 2009

Remote Tuner Update

Apologies to any readers for the lack of recent updates. I’ve been busy sourcing components for the tuner RF deck and I’m just about there. I’m waiting for a pair of matched roller inductors to arrive and unfortunately they are about 8 weeks away. I’ve been trying to avoid paying the earth for them and although I’ve found some cheaper possibilities I either wasn’t happy with the condition of them (very well used) or they were not a matched pair. I considered butchering my Palstar balanced tuner (AT1500BAL) but decided against that as I might want it or may sell it to fund this project.

I decided to go with a vacuum variable cap for a number of reasons. Firstly they are available with very low minimum capacitance (5pF) and secondly they are multi-turn devices (the one I’m using is 16 turns minimum to maximum capacitance) giving me an easier time with the stepper motor drive arrangement i.e. no need for a reduction drive. All I need to do now is work out the end travel limit switch arrangements which will probably use a threaded bar with a travelling nut that operates a couple of micro switches.

73 Paul


  1. Hi Paul
    How about a belt drive, a pair of pullies and an encoder for the end of travel limits, once calibrated you just need to count 🙂 I’ve seen this arrangment used before on vaccum caps.

    • Hi Kevin,

      I think it’s simpler than I initially thought. The cap has a peg that moves along a slot in the drive end of the cap. All I need to do is extend it using some insulated material and that will operate a pair of micro switches (one at each end of the travel)

      73 Paul

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