Sunday, April 5, 2020


     Having decided I need a 1:1 balun -- a kind of RF transformer, used to connect unbalanced (ground-referenced) equipment to a balanced device (like my G5RV antenna) -- I found a ferrite toroid core that seemed likely, wound two interwoven 12-turn coils of #14 house wire on it (as much as would fit), and looked around for an enclosure.

     I didn't have much, and then I found my collection of old tea canisters.  That worked.
     The coil is sandwiched between two 1/8" Garolite* plates held by brass screws (one headless) into a ceramic insulator; another, shorter insulator is threaded onto one end and fastened to the bottom of the box.  The lower plate has two corners clipped so the wires from that side can get to the terminals.
     There's a trick to working with such thin metal.  You can drill it, but it's risky -- even with a backing, it can catch and tear.  A better bet is to mark hole centers with a sharp awl and use a Roper-Whitney punch,† which will center up on the awl-made dimples.  Careful work with a hand reamer or chassis punch will enlarge the holes if necessary.  Small holes can just be punched with the awl, especially in places the punch won't reach.  (The lid does fit square, when properly seated.)

     My little SWR analyzer says it's not terrible on the 80 meter ham band and not bad on 40 -- the ferrite I used was supposed to be good through 30 MHz, but the match starts getting worse and worse by the 20 meter band.

     Checked it with the RME-45 receiver and Millen "Junior" transmatch and it works okay, slightly better signals with it between the antenna and the matcher.  80 meters was a jumble of noise this afternoon.  Just went down (10:20 p.m.) and turned on the receiver; as I tuned past 3885 kHz, a voice came out of the speaker: "Hello, Bobbi!  C'mon Bobbi..." 

     That got my attention, as you might expect.  I dodged the slow-rate tuning back and forth a little, and he came back on, "[callsign], this is [other callsign], c'mon, Bobby, if you're not there I'll just call CQ, CQ, CQ , this is [other callsign] and remember, people, don't buy coax jumpers, you build your own.  CQ, CQ, from [other callsign], c'mon..."

     So I wasn't hallucinating.  And I was certainly glad I'd made my own coaxial jumpers!

     Next step, rebuilding the transmit/receive switch and moving the DX-60 transmitter over to the new shelves.
* As close to Bakelite as you can get now.  McMaster-Carr stocks it in a variety of sizes and shapes.

† Mine is actually a Whitney-Jensen, an earlier model with a few minor differences.  These useful little devices are widely available used. Plugging the name into a search engine brings up a lot of listings at online auction sites.