Last week, Dave KD2FSI brought his AlexLoop to the monthly South Plainfield Amateur Radio Club operating night. I was impressed by how easily it went together and how relatively easy it seemed to tune. I would love to have one myself, but the retail price is a bit out of my budget, so I decided to homebrew one, instead.
Last night, I ordered 25 feet of LMR400 from DX Engineering - enough to make two loops with left over to spare. Then I went and purchased a 20 - 240 pF air variable capacitor from RF Parts. I already have some PVC for a frame - all I really need is a box for the enclosure for the capacitor.
I've read several articles by Steve AA5TB, Julian G4ILO and others. I think I have the construction concept down and if all goes well, in a few weeks, maybe I'll be playing around with a W2LJ Loop. The only thing I'm not sure of, and have to think about, is how I'm going to get this to mount to my Buddistick tripod.
I think I may have to bug Dave again and take a look at how his mounts to his tripod.
As I build, I'll take plenty of pictures and will post the saga here.
72 de Larry W2LJ
QRP - When you care to send the very least!
Larry,
ReplyDeleteI am also working on a loop. My plan for the tripod adapter is adapt the pvc to a MPT, screw in a pvc threaded plug drilled and tapped for 1/4 inch bolt thread.
de Paul N0NBD
I could only find a 20-240pf capacitor on the RF Parts website. Was your 2-240pf cap a typo?
ReplyDeleteIf not do you know the part # that you purchased? I'm anxious to build this loop as I follow along.
Phil K7TTI
Sorry about that! Type on my part - yes, that is a 20-240pF cap. It came in the mail on Saturday. It's a bit bigger that I had envisioned. Have to look for a suitable container.
ReplyDeleteHmm. When AEA used to make the IsoLoop, there was a reason they used a butterfly capacitor -- even though it halved the total effective capacitance in their loop, as well as reduced the useful rotation from 1/2 a turn to 1/4 of a turn.
ReplyDeleteYou see, in a magnetic loop, there are extremely high currents involved, and the contact area of the brass strap that makes the electrical connection to the rotor plates is quite small. At higher power levels, you could see significant heating, and any such loss is power that isn't radiated.
AEA used a butterfly capacitor connected in series because there is no need to use the rotor connection, which greatly reduces the loss and increases the Q of the capacitor.