Converting old scope into Radio Direction Finder (EMI finder) - Page 1
Forum section: electronics / projects

author: Cyberdragon
author_rank: Super Contributor
timestamp: September 10, 2016, 08:04:40 pm
content: I have an old Waterman Electronic Products portable oscilloscope (S-11) that I got from a set of two, one of them has been repaired , the other is crusty. I was thinking about gutting the dead one and using the CRT and chassis to make a simple radio direction finder.Don't know much about RDF but here's my idea. My thought is to have a hand-held array of four antennas of some sort that would go into a set of four wide-band preamps in the machine. The signal would be rectified to DC pulses that would be sent to each indevidual deflection plate driver. This should create a line that points to the direction of the strongest signal.The problem is the hysteresis that would result from multiple strong signals. The gain would be very weak though, just to look for local interferrence like power supplies. Any ideas?

author: Cyberdragon
author_rank: Super Contributor
timestamp: September 11, 2016, 12:42:34 am
content: I'm only going to use it for basic noise detection around the house and neghborhood (smart meters, bad transformers, exc), so I am going for a very basic setup. I just need it to give a rough direction and strength, I don't need the frequency spectrum. This is more of recycling junk into a neat gadget, I love working with old tech, but I do want it to be fully stand alone. I call it an RDF but more of a directional EMI detector (IE wideband noise).As for the antenna, I want to use multiple antennas instead of a mechanical method so I don't have to use a servo that could possibly introduce its own noise. Bulk does not matter, as long as it can be held, this won't be battery operated so it won't be able to move far from a plug. I'll ask some of the guys in my antique electronics club what type of directional antennas they could sell to me (If they have a rotating one I'll use that and modify the system accordingly).

author: Cyberdragon
author_rank: Super Contributor
timestamp: September 11, 2016, 02:55:14 am
content: The reason I want to build a direction finder and not a simple receiver is that the noise may be coming from another property and I don't want to trespass. Plus it would be faster to just go "oh, it's over there" instead of hunting with a detector. I can always use a detector and oscilloscope on the signal after I've found it, I may even add connections to feed the signal into headphones or a scope.I think the simplest would be four yagis (I'm sure some of those radio-heads have those laying around somewhere). The CRT would just have a simple compass display for direction so they wouldn't have to be very narrow.

author: tggzzz
author_rank: Super Contributor
timestamp: September 11, 2016, 06:33:36 am
content: Quote from: Cyberdragon on September 11, 2016, 02:55:14 amSutely thesimplest(as well as cheapest, fastest) would be one yagi and some of evb49's suggestions.That would also be portable, so you could walk along the property line or even around the neighbour's property. That would give an even better localisation of the source.