10631Re: Varicaps vs old fashioned variable capacitors
- Jun 20, 2014Hi Joe, thanks for the post. I'm quickly amassing a small army of loops so I can learn for myself all of the good advice I've been getting. The first little tidbit of reality comes from comparing my recently homebuilt loopstick (Palomar clone) with my newly acquired Quantum loopstick from eBay. I needed a "standard" by which to compare my home built attempts. So far, my homebuilt model compares very favorably with the commercial version. I need to quiet things down electrically by getting some matched JFETs and paying attention to critical component values to keep the balanced amp really balanced. If I substitute a regen type preamp circuit I can improve the Q as well. My plans for the loopsticks are to build a remotely tuned outdoor model and possibly springing for a monster ferrite rod from Stormwise to replace the current Amidon 7.5" rod. I've become a big fan of remote tuning as I've been playing with stepping motors for the past year or two and I've built a few that use simple cat5 wire making hookup easy.
The big surprise is how much better even my 30" passive air loop performs against the loopsticks. Of course I was aware of this but there nothing like actually observing it myself! My next steps are to compare tuning the loop with varicaps vs the air variable cap and to try getting the best inductive match to my 50 ohm feed line. Additionally I want try connecting a balanced preamp directly to the resonate loop and observe the performance of that arrangement vs the passive coupling approach. Another few months and dollars later I'll finally be up to speed on what everyone else already knows! Well at least I'm having fun doing it!
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