I put aside the little Arduino project I'm helping my friend with so I could do some "Shack Renovation" this weekend.
Actually, it was more a "Clean-and-Toss" event, where I cleaned up a bunch of stuff, got some stackable storage bins, tossed out several LARGE cardboard boxes that I had "stuff" stored in, and in general neatened things up a bit.
One of the things I did was to get my ICom IC-R7100 and Uniden BC796D receivers set up, and fed them both off the little multicoupler I built sometime back.
The simplest way of looking at a multicoupler is to consider it a "Splitter with Gain", although it does more than that. It also provides 30~40dB of isolation between the receivers, which is good for keeping things like Local Oscillator leakage down to a minimum.
WELL....it's not working the way I intended, and rather than spend HOURS fixing it (trust me...it would take me longer to "fix" it than it did to *build* it), I decided to just leave the Uniden scanner connected to the Discone, and get a little 3-element Yagi that I can point at the airport so I can use the ICom to listen to all the airport stuff.
Yes, I know, it's a terrible waste to use an IC-R7100 to "just" listen to the local airport, but until I get the damn multicoupler working (looks like the amplifier isn't), that's what I'm going to use it for.
Well, me being me, I decided to build an airband Yagi, rather than buy one. I tend to be CHEEP about these things, and I've got piles of 1/8" and 1/4" brass and aluminum rod for the elements, and a ton of PVC pipe to use for a boom.
ANYWAY....snooping around the web for a while, I couldn't find any cookbook dimensions to build a 118~137MHz Yagi, so I figured I'd gin my own up. Gee...there's all these neat antenna design programs for Linux, so I'll just grab a couple and........
NONE of them do what I want! Oh sure, they'll all give me great plots of gain, directivity, and patterns, but that's AFTER I've figured out all the element dimensions!
So, it looks like I'll have to start with a dipole cut for 127.5MHz, and then go with the old rule-of-thumb making the reflector and director 10% longer/shorter than the driven element, and then tweak the dimensions of where the elements are spaced on the boom until I get something that looks like it will work.
Maybe I should have just keep going building another one of the Arduino units. I've built three so far, and they all work "As Advertised".
OK....found a website that does *exactly* what I needed to do. It let me design a 2-element Yagi, that has about 3dB gain, and fits on an 18" boom.
You just enter the center frequency, a gain you'd like, a few other specifics,and it generates the element lengths, and spacing.