Currently in the process of building a 121.5 MHz yagi, but it stumbled across my mind that I wouldn't be able to find a 406 MHz beacon (from far away, as the 121.5 homing signal is weak in a 406 transmitter). I guess my first question is, is the sweep tone transmitted on 406 as well as 121.5? This also means I'd need a UHF transceicer to connect to my yagi, any inexpensive models? As for "why" I'm doing this instead of just utilizing CAP aircrews, the weather here is usually bad, especially in the mountain passes (which is the only route for most GA flyers. Thanks for the help!
The 406 MHz signal is a roughly half second burst of digital data sent every 50 seconds at 5 watts. The 121.5 homing signal is continuous except during the 1/2 second data burst. Minimum power on the 121.5 homing signal is 25 mW and can be as high as 100 mW per spec. For reference, a standard Pointer 6000 practice beacon is 100 mW. Some 406 beacons are dual antenna, one for 406 and one for 121.5. Most are single antenna optimized for 406.
There are multiple 406 frequencies used in beacons, in non-standard frequency steps. Most low end receivers can't tune all of them.
Mike
PM me. I have all the information already in PowerPoint including an inexpensive tracking receiver that can work both 121.5 and 406. On the 406 you can see multiple transmitter frequencies at once. This is the same system as I posted previously. I have several units in SWR that have already began assembling the systems to use locally. I will be glad to share the information with you also.
Previous post.
http://captalk.net/index.php?topic=22838.msg413267#msg413267
I have updated the presentation for the 406 Tracking system. It is available at https://drive.google.com/open?id=1lkVCaGf_aBgpjhbtRVSnEI5WbwtrgCU4
Excellent work! The neat thing for me is that I already have all the stuff. Do you mind if I use your presentation in my Squadron ( or Group, and maybe even Wing)? I will, of course, acredit you.
Sent from my SM-G935V using Tapatalk
Normally you'd use the 121.5 signal for terminal guidance, but if not available it is possible to geolocate a 407 MHz ELT using signal strength of the data pulse alone, using a common air band radio with digital signal strength indicator.
The method used with success is to carefully note your own location on a good map, record the pulse strength (recommend 2 - 3 pulses for accuracy), then move to a series of new locations and repeat. For example, take data at road intersections, or along a taxiway. Plot the data, drive back to the high strength plot, and repeat along an intersecting axis. When we came up with this method one dark and stormy night, I used an airfield plate as the map and it worked fine, leading us to the hangar complex behind which the new aircraft (with new beacon) was shielded.
More than I would have believed, we have been called to find unencoded 406 beacons (no tail #, no GPS, no info at all) and this method worked great when we first used it, six years ago now.
R/s
Spam
Quote from: Fireball on July 16, 2018, 07:00:47 PM
Excellent work! The neat thing for me is that I already have all the stuff. Do you mind if I use your presentation in my Squadron ( or Group, and maybe even Wing)? I will, of course, acredit you.
Sent from my SM-G935V using Tapatalk
Yes, you have my permission to present this. I hope to give a presentation this weekend for Texas wing. Depending on time at the SAREX.
Quote from: Spam on July 16, 2018, 08:06:01 PM
Normally you'd use the 121.5 signal for terminal guidance, but if not available it is possible to geolocate a 407 MHz ELT using signal strength of the data pulse alone, using a common air band radio with digital signal strength indicator.
The method used with success is to carefully note your own location on a good map, record the pulse strength (recommend 2 - 3 pulses for accuracy), then move to a series of new locations and repeat. For example, take data at road intersections, or along a taxiway. Plot the data, drive back to the high strength plot, and repeat along an intersecting axis. When we came up with this method one dark and stormy night, I used an airfield plate as the map and it worked fine, leading us to the hangar complex behind which the new aircraft (with new beacon) was shielded.
More than I would have believed, we have been called to find unencoded 406 beacons (no tail #, no GPS, no info at all) and this method worked great when we first used it, six years ago now.
R/s
Spam
The nice thing about the system I am working with is if you miss the pulse, you have about 45 seconds or so to look at it in the waterfall portion of the display. The visual of the pulse make it easier to "see" the strength. Similar to what you are doing with the Signal strength meter. Being recorded visually, you do not have the lag of a mechanical needle. This equipment has been able to be 1st twice in the two competitions it has been used in. Both times were at an airport with the beacon hidden in areas the 121 signal bounced all over the place. The 406 for some reason went through the metal hangers without much if any reflection.