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View Full Version : Downed Plane Foxhunt....



SENTRY
26th July 2011, 02:04 PM
The following idea would not help for a plane that doesn't have video gear still powered when it crashes - but I've been lucky enough to find all my downed planes via the video link still broadcasting.

The issue is that my "foxhunts" get harder and harder the closer I get to the rig. What if we can develop a VERY narrow beam antenna that works close to the plane to "zero in" once you're close enough that the body-blocking no longer works (body-blocking is less effective the closer you get to the rig). The beam would have to be ULTRA narrow, and no reception on the lobes. Basicaly this antenna would need to have ONE sweet spot - w/ dead zones all around that spot.

Mark Hitchman
26th July 2011, 02:20 PM
An attenuator on the receiver may do the trick. I was out testing my video signal with a few different antenna yesterday and found that my 9dbi yagi had a range of ~15 meters with 2 X 26dbi attenuators on the receiver and it made it VERY directional at that distance. May be worth a try.

Mark

SENTRY
26th July 2011, 02:25 PM
Great idea Mark - didn't think about that... once I find something that works I need to keep it in a holster and ready for action. :)

Technoweenie
26th July 2011, 03:32 PM
A variable attenuator that you can toggle in more and more attenuation works good. As you get closer, add more attenuation. If your looking for a lost plane beacon on VHF / UHF, a radio with a signal strength meter helps too.

Try building one of these. An ARRL switched Attenuator from the ARRL Handbook: I've used mine many times:

http://www.arrl.org/files/file/Technology/tis/info/pdf/9506033.pdf

Looks like this one. Best to put in shielded box:

http://www.vk2zay.net/article/100

IBCrazy
27th July 2011, 07:29 AM
You are going to want a few stages of attenuation. 10 db or less is going to do precisely nothing for you. I'd get a 20db and a 30 db attenuator. You can find them on EBAY for less than $20 each.

-Alex

SENTRY
30th July 2011, 11:49 AM
Got a link to some GOOD attenuators??

Mark Hitchman
30th July 2011, 03:12 PM
I use a couple of these 26dbi attenuators (http://cgi.ebay.com/MACOM-ATTENUATOR-DC-4-GHZ-26DB-SMA-2082-6175-26-/300519894498?pt=LH_DefaultDomain_0&hash=item45f861ade2#ht_557wt_961)

Mark

GLEvideo
31st July 2011, 10:24 PM
My wife and I used to go on regular Transmitter hunts and we got to where we were winning many of them. I learned a lot from that experience and the most important thing I learned is that when you get close to the transmitter, instead of sweeping with a beam to try to find where the TX is, you sweep with the beam to find where it isn't. Stop looking for a peak in signal. You won't find one when you get too close because your RX is overloaded with RF. Use an antenna with a very sharp null and hunt for a reduction of signal. Start farther out and triangulate several headings by finding signal peaks then move in close looking for the null.

cabster101
1st August 2011, 12:58 AM
What about just putting one of these GPS trackers on your plane? I was thinking about doing it on a zephyr I'm currently building.

http://www.amazon.com/Little-Buddy-Child-GPS-Tracker/dp/B004H1K9H2/ref=sr_1_14?ie=UTF8&qid=1312174103&sr=8-14

That way you could use your smartphone to pinpoint the exact location and it has its own battery that I read last for 24 hours.

I saw one of the guys from Flite Test using it on his maxi swift on youtube. http://www.youtube.com/watch?v=sJ9AZilcIpM

Adrenalinrush
1st August 2011, 06:29 AM
I will take some pictures the next time I crash.

Where I fly the over growth is hideous.

I was at the field yesterday and an Extra 300 went down in some brush, we were 10 feet from it and couldn't see it. Finally, the old guy that owned the plane had his wife bring a chainsaw and it took us 45 min to go 20 feet into the brush just to get to the plane. When my little foamie hits a tree, I have a general sense of where it is (plus my border collie gives me a general direction), and I start moving into the bush. When I get in the general area I start working the throttle and listening for it. I am crusing the stryker atm, so the prop is usually in the air and can freely spin, but I can hear it WOT from 100 yards away or so. I do fly pretty close (i.e. within a mile of myself) so the throttle and listen works pretty good.

I am truly an expert at finding downed planes, from the amount of time I spend looking for it / how much time I fly.