Comment on Series coax stub capacitors for more precise loop antenna tuning
einfach_orangensaft@sh.itjust.works 6 days agoYeah i am planing to build a remote controlled coax capacitor eventually (probably something like this: …dxfreun.de/…/Abstimmbereich_MagLoop.jpg ) but right now i am still waiting for some parts to make that happen.
The additional high voltage durability of the serial coax capacitor is nice, (should be now 5kv, since a single RG58 has 2.5kv) but i doubt i gona need that with my 4W Tx ^^
fullsquare@awful.systems 6 days ago
i’d expect shield to fray and core to bend with arrangement like this. if you just slide piece of pipe (can be rectangular, or U-shaped) it should be more durable. you’d be surprised at voltages developing there, even with 4W online calculators suggest something in 1kV range. 100W is over 5kV
einfach_orangensaft@sh.itjust.works 6 days ago
i thought about a bicycle rim :D but i kinda wana keep this a mobile setup…
i have been thinking about inflatable loops recently, sadly i was only able to find a singular example of those (some guy slapping some aluminum foil onto a inflatable swimming tire and it didnt work that well).
My idea would be to take some copper braid sleeve (5cm diameter) and put a inner bike tire thru that. As far as i can tell nobody has tryed that before…and i keep wondering, if i add a small electric pump to the setup i could maybe tune the loop by inflating and deflating it while using a non variable capacitor.
fullsquare@awful.systems 6 days ago
the thing with using aluminum tape is that you can get away with very small thickness, because current flows only in top tens of micrometers depending on band. you can just roll up, say, 5cm wide, 0.5mm thick aluminum tape and have riveted or maybe brazed short length of 2mm thick bar to the ends for connecting capacitor. the problem is with mechanical stability of this setup, which is why you see pipes and thicker bars, bicycle rims etc
with braid you get a lot of contacts between wires, and i’m not sure that resistance of them would be low unless tire is fully inflated. maybe you can put short U-turn within loop at end opposite of capacitor and have adjustable shorting bar there. adjustable capacitor is more common by far, because if you can adjust it widely enough, you can get to different bands
einfach_orangensaft@sh.itjust.works 6 days ago
Good point with the copper sulfide, that wasnt on my mind at all, if i try ill put a protective layer between the braid and the tire rubber
Yeah i heared about the skin effect in aluminum being much shallower than in copper negating the better conductivity of copper, but i didnt found aluminum braids.
On the point of braids, i was thinking that would probably work well since the shielding in coax is also copper braid and many loops are made out of coax, but big diameter coax cant be folded as good due to the core, so i was thinking…maybe just use the shielding and no core at all.
You are right with the dipole, that would probably be the most sane solution. But i cant get the idea of a inflatable loop out of my head now…