Just got back from vacation so late on the direction finding stuff: there are other techniques using a pair of small antennas mounted to a horizontal bar and a modified receiver which allow relatively accurate direction finding at VHF frequencies. However the equipment is not cheap and not really small, and would have to be adapted to be accessible.
i don't think it would perform at all as well as merely listening for the aforementioned bell on the dog's collar. Or just teach "speak" before the off leash training. BTW, the government and commercial surveilance of homes with illegal receivers were looking for the "local oscilators" of the heterodyne receivers. Knowing which frequencies they were looking for depending on available chanels etc. all they had to do was see if the expected equipment was in the home, so no really accurate direction finding is required. We once built a gizmo with a hand held unit containing a number of bright LED's that were modulated at an audible frequency. There was a "mobile" unit that was merely a photodetector and a high gain audio amplifier with speaker. So, within a range of maybe 20 feet, if you pointed the light in your hand at the mobile device it would make a tone. You could aim pretty well accurately because the tone got louder as your aim got better. But the range would be pretty short and the sun would overload the photodetector so that the sensativity would not be reliable. This was supposed to be involved in testing the abilities of different bats to 'point". i don't think the experiments were ever done. tom
