A couple thoughts. I have a very low cost audio tag device comprised of a handheld transmitter that can alert four different beepers to sound. It works up to about 50 feet, and the beepers are hardly the size of a hollow wean chocolate bar.
You can also achieve direction finding with two ferrite stick antennas mounted at right angles. You will not get forward and backward definition, but you can sure get two accurate 180 arcs. Geoff ----- Original Message ----- From: Dale Leavens To: [email protected] Sent: Monday, November 26, 2007 12:12 PM Subject: Re: [BlindHandyMan] radio direction finding project In order to accurately locate a transmitter you require triangulation. the wider spaced your receivers are the more accurate will be your location. You point a very directional antenna swinging it side-to-side judging the strongest signal then plot that line on a map. where there are two receivers placed at distance you can plot the intersecting points of the two directional lines and that should be within a few hundred feet of the source of the transmitter. Otherwise you have to move your s ingle receiver then take another direction and plot that. If the target is moving of course your lines won't cross in the right place. If you have enough satellites in the air you can judge location more accurately and readily by comparing the signal from several angles simultaneously. this is essentially how locater beacons work. GPS on the other hand also uses a number of satellites but a little differently, it knows which satellites it is receiving at any point in time and where they are supposed to be and how long it takes a signal to arrive from that distance. Knowing that the device can estimate pretty accurately just where it is. Well anyway, that is more or less how it was explained to me. I understand that during the bombing of Britain the German forces sent two highly directional signals out from distant points in Europe pointed to merge over a particular city, say Liverpool. A flight of bombers could pick up a signal then follow it and listen for the complementary signal then drop bombs. It was somewhat approximate but in black-out conditions there wasn't much else to go on. Jamming further confused the accuracy but this was a mixed blessing resulting in otherwise non-strategic places bein g bombed. Sorry, didn't intend to drift that far off topic. Dale Leavens, Cochrane Ontario Canada [EMAIL PROTECTED] Skype DaleLeavens Come and meet Aurora, Nakita and Nanook at our polar bear habitat. ----- Original Message ----- From: Dan Rossi To: [email protected] Sent: Monday, November 26, 2007 10:15 AM Subject: Re: [BlindHandyMan] radio direction finding project I know very little about this radio stuff, but what about using a loop antenna for direction finding. That's how they do those radio fox hunt games. A transmitter puts out a signal and a bunch of radio-heads with loop antenna, run around trying to find the transmitter. -- Blue skies. Dan Rossi Carnegie Mellon University. E-Mail: [EMAIL PROTECTED] Tel: (412) 268-9081 [Non-text portions of this message have been removed] [Non-text portions of this message have been removed]
