Antennas

Dual Band Yagi Antenna 145 & 440 Mhz

This antenna is based in part on the WA5VJB LEO satellite antenna, and uses spacing and element length from the DL6WU Yagi calculator and the ARRL Yagi page.

I tried several methods of feeding the antenna, and even tried using a single radiating element for both 145 and 440MHz, but I could not make the antenna behave over a wide enough bandwidth.  So I ended up using two separate driven elements, and connected them to the duplexer that I built, described below.  I ended up settling on the folded-dipole feed.  Direct coax feed worked, but it seemed like the antenna bandwidth suffered.

Portable 440Mhz Ground Plane

Made with copper-clad 3/32 welding rod and a PL-259 coax connector, this antenna presents a low SWR over most of the 70cm UHF ham band.  I dipped the tips of each of the elements in Liquid Electrical Tape to make the ends less likely to scratch or tear anything.

Dog-Food Duplexer

I don't know if it's correct to call this a duplexer, or a splitter, or what; but this device takes the output of a transmitter and splits it into 145 and 450 Mhz outputs for two different antennas, using a low-pass and high-pass filter respectively. Or in the case of the dual-band yagi shown above, this little box connects to the two different driven elements on the yagi.

I call it a "Dog Food Duplexer" because I used a piece of empty dog-food can to create the metal circuit board shield of the duplexer.  See those ridges?  That's from the dog food can.  I didn't have any solid copper-clad circuit board on hand, so I used what was in the junk-box, (and in the recycling bin as it turns out, for the dog-food can shield).

The capacitors were what I had on hand, and were only rated for 100v -- So I would not want to run very much power through this duplexer/splitter.

An article in an old back issue of QST magazine was the inspiration for this.