Well-Known MemberTRF Supporter
- Nov 25, 2009
- Reaction score
- Central Illinois
Oh shoot. Back in the "old RDF days" I saw the "old-timer fliers" rotating their Yagi receive antennas in their hands to try to get the maximum position signal trying to match up the Yagi antenna polarity to the transmitter as a rocket was falling under drogue. I studied to be a Ham radio operator with a "General" license soon after back then and realized what the heck they were doing with my study! Knowledge is power I tell you!One thing that's not been called out here but I feel worth mentioning is that all of our transmitters (for the most part) are using 1/4 wave whip antennas. These antennas have polarisation, as do yagi antennas. Last year I was tracking a TeleGPS and noticed my SNR was lower than I expected. I could rotate my 5 element yagi 90 degrees to where the elements were in a vertical orientation and my SNR would improve dramatically. I didn't really catch onto what was happening until I got to the rocket. It was in a sea of canola and the chute had caught itself in the canola which resulted in the nose cone hanging off the canola in a vertical orientation. So my transmitter antenna was in a vertical orientation, and turning my yagi to match that orientation improved SNR dramatically.
TLDR, if you aren't getting a good signal on the ground try rotating your yagi 90 degrees.
Those oldsters were trying to match antenna polarity so they could get the maximum range out of their RDF trackers of the time by twisting their arms about their wrists right and left. Get a signal peak and follow it down.
Pointing a Yagi is not a problem but getting the polarity right for reception is priceless. Hence, "rotate the wrist." I saw that technique used back in the early 1980's with RDF with the "older rocket guys" and it has stuck with me since. The rich fliers had the Walston stuff and I think there was a "Rocket Tracker" commercial RDF tracker in days of old. Never lost a rocket myself with RDF though I switched to GPS tracking very quickly as it was so more precise. I still use a 900Mhz Yagi antenna to hunt downed rockets on 900mhz GPS tracking as the rocket is not moving and it's easier to aim a 900Mhz Yagi at a downed rocket. I still "twist" my wrist around with my hand held Yagi antenna to "peak" the signal receive input. Gets more position packets in that way more reliably. An attenuator doesn't help for RDF until one gets close to the tracker/rocket position and is not needed for GPS/APRS tracking. There are no 900Mhz RDF trackers as the ground footprint is small at that frequency. Although I found out it's pretty decent with a multi-element 900Mhz Yagi antenna pointing at the presumed rocket position for ground recovery.
I don't care if it's RDF, GPS or APRS tracker. Point a Yagi receive antenna in the direction of the downed rocket and you'll at least know you'll get it back sooner rather than later. The 900 Mhz stuff works fine when the rocket is downed. If it's a GPS tracker and it still has a view of the satellites on the rocket, one will get a final position. A 900Mhz reciever Yagi will tell you sooner rather than later you'll get there as long as you know where to point it. I like that.
For lawn darts, I've witnessed with RDF and GPS tracking that one can get to the "hole" and see the fincan sticking out of the ground. With RDF, if someone was out in the field takig a fix, when a rocket came down, can "cross" the fix lines from the guy/gal out in the field and the flier from the launch site on a map. Can at least salvage motor components and "dispose" of the rocket "trash" stuff and dorked electronics in an appropriate manner after the digging up! Been there and done that myself actually. At least the electronics gave up their lives so I could dig the rocket out of the ground and dispose of the batteries appropriately. Sometimes, only see the fincan sticking out of the ground.
Though I've seen many folks doing RDF by themselves able to "walk a line" out to the last known direction fix and get rocket remains back if the deployment events didn't occur properly! GPS rocket tracking makes it easier. Kurt