At 09:12 AM 7/1/2013, John Ferrell wrote: >A long while back I sometimes used a 440mhz Yagi to pick up commercial >UHF TV. The pattern made no sense at all, but rotating the antenna >would find a sweet spot. >The antenna was already up and in use as an amateur radio antenna. This is something vaguely related to what John mentioned: some friends of m= ine do a lot of Pyro and Fireworks stuff and they use wireless links for=20 stuff that they can't run wire for. Think of Chuckwagons moving=20 about at the Calgary Stampede. Anyway, they called me a couple of months ago and asked if I could=20 look at the antennas for their wireless links. They have two=20 different link systems (different manufacturers) and the=20 rubber-duck-style antennas look similar for both. But they've been=20 having problems and swapping antennas seems to make the problems go=20 away. So: they thought that the two different links might be using=20 different frequencies and wanted me to identify which antennas=20 belonged with each of the links. Turns out that both links are in the 915 MHz ISM band. But doing a=20 wide VSWR sweep on the antennas showed that several of them had two=20 response nulls - a strong null at 915 MHz and a somewhat weaker null=20 at about 450 - 460 MHz. I took those antennae apart and discovered that the coax shield had=20 NOT been soldered to the brass tube that makes up the lower part of=20 the dipole. Oops. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .