ssd's Emergency J-pole pictures
coiled 2m emergency J-pole (ladder line)
2m emergency J-pole (ladder line)
first attempts at a small loop direction finding antenna for 200mhz and below
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.
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
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