ssd's Emergency J-pole pictures


coiled 2m emergency J-pole (ladder line)
small large

2m emergency J-pole (ladder line)
small large

first attempts at a small loop direction finding antenna for 200mhz and below
small large

Emergency J-pole

This is just a handy 2m / 70cm antenna to have around. Every ham should have one of these. They're trivial to make. Essentially, the bottom section is a quarter wave transmission line, and the top section is a dipole. Connect your coax at some point on the transmission line to best match impedance. Some designs add some capacitance too. Plans for this are on my link page.

Small loop

Both loops are less than 5" circumfrence. A small loop is 1/10 or less of the target wavelength to get optimum directionality. These are useful for direction finding -- to try to aim the dish above or find noise interferance. Loop must have a balanced input, and work better with a groundplane. Electrostatic shielding and ground plane wires were attempted. Results varied wildly, but the antenna was effective enough to triangulate a noise source at 20' or more. Worst problem is that the antenna's null is not deep enough, so strong signals are hard to pinpoint. 15-20 feet is about the minimum useful distance with even a weak signal. A balun is sure to help increase the null and make the pattern less like a cartoid.

 

return to ssd's Antenna pictures
return to ssd's ham links page