Burt Lang wrote: > The 10pf would probably work for the cans where the notch is on the low > side of the pass ie hi-pass BpBr. The capacity required for the notch > on the high side is 20-30 pf. I have paralleled 3 of the 10pf caps > (which can be had surplus for $1 or so each) to replace the 30pf caps. > It does help when modifying it in this manner to have the proper tap for > the threads (15/64x64tpi). It is not exactly easy or cheap to find such > a tap. > > To explain the action of the capacitors, look at the wide response (+/- > 15MHz) of the can. You will see that there are two notches, one on each > side of the pass peak. The notches are at least 10 MHz apart. The two > notches move in tandom with changing capacity. The more capacity the > lower the notches are. With low capacity the lower notch will cosy up > to the peak. In order to lower the upper notch down close to the peak > requires a lot more capacity. > > Good luck with your tuning. > > Burt VE2BMQ>> > > tomnevue wrote: >> snipped > >> Now for general information, the nut is just a locking device and the >> capacitor is screwed into the threaded mounting plate. Also it was >> pretty easy to find Johanson hi-Q piston caps at 0-10pf which are about >> 1/4 inch shorter. I was curious to see if this was enough capacitance >> to resonate the loop at the right frequency, so I temporairly installed >> one of these. I added a strip of copper to take up the added length. >> With the 10pf capacitor it resonated well into the Ham band, but I'm >> sure it wouldn't make it down to the cavity lower spec of 137MHz. So in >> a pinch, I think the shorter 10pf version would probably useable for 2 >> meters. >> >> Thanks again. Tom > > > > > > Yahoo! Groups Links > > > > >
