Post subject: How can I make a very directional AM antenna?
Posted: Mar Thu 29, 2012 2:09 am
Joined: Aug Fri 03, 2007 1:06 am Posts: 112 Location: Upstate South Carolina
I am using a modulated 560 kHz radio signal to find a defective (buried) lawn sprinkler system valve. I connected a signal generator to the wire going to the defective valve at the timer, earth grounding the other lead, and use a radio to follow the wire along the ground. It works fine except the radio is too sensitive to narrow the location down to a small area. Reducing the generator signal level or the radio gain does not help. What I think I need is a very directional antenna that I can aim at the buried wire. I can adjust the generator signal level from millivolts to about 20 volts so antenna sensitivity is not critical. Any ideas?
Post subject: Re: How can I make a very directional AM antenna?
Posted: Mar Thu 29, 2012 2:26 pm
Joined: Jan Thu 01, 1970 1:00 am Posts: 13822 Location: Utica, NY 13502 (USA)
Just about any transistor radio with a built-in ferrite rod antenna will work as a direction finder. They produce a very sharp and deep null when oriented lenghwise toward the signal. There will be another null 180 degrees in the opposite direction but, in this case, you know that the valve isn't toward the sky.