CAP Talk

Operations => Tools of the trade => Topic started by: Paper Machete on June 24, 2018, 03:22:08 PM

Title: Building a 406 MHz yagi
Post by: Paper Machete on June 24, 2018, 03:22:08 PM
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!

Title: Re: Building a 406 MHz yagi
Post by: sardak on June 24, 2018, 04:11:12 PM
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.

Title: Re: Building a 406 MHz yagi
Post by: GZCP31 on June 24, 2018, 07:28:34 PM
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.

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