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About Jlerch

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  • Birthday 01/27/1969

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  • Location
    Tampa, Florida
  • Interests
    FPV fixed and rotary wing aircraft<br />
  1. Here's the beach video. The ground station is located at the large concrete building seen at the 1:35 second mark. Not the most desirable position, and it showed a few times. Apologies for how jerky this one turned out, I was out near the water flying direct, while the glasses and ground recorder were passed around the family. I look forward to getting out and trying again with a proper setup, should be fun
  2. Ok, Here is a follow up. In a nut shell, this setup is much better than I had before on the other airframe. If its because of the antenna or just the way it was installed, I don't know, but its working great. For the first time I was able to record a whole 10 minute flight with out my ground recorder giving the video input the finger after a loss of signal. I still don't trust the system yet, that will take a little time, and the only complaint I have is the little white foamy airframe is darn near impossible to find when transitioning from FPV to direct observation. Once I get my Eagle Tree OSD, and get it working, I'll start stretching the legs on this airframe. Having flown out of range of the 2.4ghz Spektrum radio once on the previous airframe, I am leery to get too far away at this time. Till then, here is the maiden flight as seen by the ground recorder.. (also, I seem to really get a kick out of seeing the wing and aileron surfaces while flying! ) And here is a video tour of the setup As soon as the upload is complete, I share a sunset airborne beach video that actually made my grandmother cry when I had her on the glasses!
  3. That reminds me of a good friend that landed a job with "Harris Corp" back in the late 80s. It sounded so cool on paper, he was going to be building a military Tank warfare simulator. In practice, he sat behind a terminal typing numeric values into what he described as a three dimensional data base, describing each cell's details such as altitude, collision data, color, etc. I thought that sounded kind neat until he told me they only rendered the terrain every 2 weeks, then they spent the next week debugging the existing terrain, the week after that building new terrain, re-render, repeat. I'm pretty certain he hated that job! :-)
  4. With a Homer Simpson Esque "DOH" I finally realized how sources were working in the simulator, which is NOT how I thought they worked.. After reading the Stinking instructions in the help file, I worked out the following simulations for a single RF source ant. In free space: 1 inch above normal soil 10 feet above normal soil 100 feet above normal soil 1000 feet above normal soil I still don't get why the sim says 3.24" = 1/4 wave, but clearly prefers the 1/4 wave Ant height to be 3.08" At this point, I'm going to stop playing with the sim and get back to building.. I will admit, loop antennas are starting to look interesting to simulate Thanks again for your help!
  5. The quarter wave monopole is depicted on an infinite ground plane. I have a finite ground plane, and that ground plane is only 1/4 wave in radius. I wonder how such a small diameter 'ground plane' will affect the situtaion.. Time to fire up the simulator again and increase the radius of my 'ground plane' by several wavelengths to see if I get your Infinite ground plane radiation pattern... BTW, if I wanted to use a simple half wave center fed dipole. Only the center conductor would be attached to the center antenna, what completes the circuit?
  6. I wish I knew what I was doing, because I'm doing something wrong as my ant models don't bear this rather obvious common sense solution. For instance, comparing the same two antennas in free space, one pointing down, the other pointing up Same thing, flipped over pointing up: Now same antennas, but modeled at an altitude of 120feet over "high accuracy" ground consisting of pastoral or heavy clay. Pointing down: Pointing Up: In free space the two orientations appear identical, over earth, the two antennas seem to have the largest deviation based on constructive /destructive interference from the earth reflection. So what happens when the wavelength in air is different than the wave length in copper medium? At 910mhz, the difference is shy of an inch on a full wave length. Its got to be a huge difference down in the 10s of MHZ range.. To be honest, It still makes my head hurt to think that a piece of wire 1/2 wave length long can have a measured zero volts on each end and tens or hundreds of volts measured in the center..
  7. This is one of those compromise results. The airframe may have to make a water landing, and I'm trying to keep everything above the water line. Also, the airframe doesn't have landing gear, so its a belly landing every time. I couldn't come up with an attractive solution to either problem. I finally gave up on the "point it down" approach when the modeling software clearly showed the free space radiation pattern as a big beach ball in either orientation. When modeled over ground, the pattern was essentially the same.. Of course, all this assumes I modeled it correctly, which is a HUGE assumption! Now there's a good question. Specifically, do we want the radiator to be 1/4 wave length based on the speed of light in the material the radiator is fabricated from, or the material the radiator will radiate into? The modeling software says 1 wave at 910mhz = 12.97 inches, online frequency to wavelength conversions agree. This makes 1/4 wave at 910mhz = 3.24 inch. However, is that the wavelength of 910 mhz in a vacuum, in standard atmospheric temperature and pressure, or in copper? Finally, since your asking me, I have to assume you already know the answer. Me, I'm just a guy off the street that's taken an interest in all this and am doing my best to educate myself. So, I'm probably screwing this up in a phenomenal fashion!
  8. Ok, here's what I came up with, and I'm looking for a GO or NO-GO recomendation. (Plus, exactly who else could I show this to that might have any appreciation for the work involved The center vertical is 1/4 wave long at 910mhz or 3.24 inch, measured from the top of the 90 degree SMA -> Coax connector The 6 radials are also 1/4 wave long and a made from stainless steel spot welded to the outside of the sma connector. The hot glue is there for strain relief. As Installed on my Foamy glider: As modeled at an ALT of 120 feet over normal soil. If I get the wiring done, I might get a flight in today...
  9. This is interesting. Anyone have the tools to make one and test it? http://www.edn.com/article/CA296495.html
  10. After asking a few questions, it appears that the turtled necked dipole and the one modeled on Mr.RcCam's link are not the same. The one on the link has the lower legs connected to the top radiating element. In esesence its just an odly shaped dipole The lower half of our turtle necks are not connected to the top radiator, right?
  11. Ok, Here is what I get for a center fed dipole in free space Now here is what I get for our Coax "dipole" in free space
  12. Peter, I screwed up and posted the wrong image, Try this one. Its "more right" With regards to your 4 points #1, I can only model 20 "segments", so I only get 10 segments per wire, and the resulting 5% discrepency. #2 The X/Y image of the ant is centered on the ant/ #3 tried both volt and current sources, the patterns were a touch different but not much. #4 Yes, there is a ground plane, its ~10 wavelength (3 meters) below the antenna. If I turn it off and use free space, I get this perfect looking double stacked donut. Oh NEAT!! Just played around with putting the ant "On the ground". Very interesting result. It appears the ground reflects the signal, and the two reflection constructivly interfere with each other.. I Seem to recall a thread about how much better the reception was improved by placing the receiver on the ground, I wonder if this explains it? Here's the "on the ground" results: Need to do some more experimenting here...
  13. So, I'm attempting to model our simple turtle necked dipole in a program called EZNEC ARRL No point really, other than to attempt at getting a grasp as to what's going on. So, my question is this, does this look right? I created two vertical wires, each 1/4 wave long, with a tiny space between the two. I've connected two sources, one to each of the two wires, on each side of the tiny space, and put them 180 degrees out of phase. I've played with a lot of optical design, so this feels kinda familiar, but I think I've done something odd. Here's what it looks like:
  14. Would an Oracle Video Diversity Controller help me any? IE, will it still drop Vsync as it switches sources?
  15. Thanks Gents, I was afraid of that, a splitter is actually a repeater. Garbage in, Garbage out.. So, is anyone using a DVR that works somewhat reliably? I think I'll do better once I get away from all the "Garbage" in my yard and get back out into the open country. The fades will happen less often, so the DVR should keep going. However, I want to be able to count on the DVR for the time when I put the airframe in. Not having a video to go look at and triangulate off of is going to really "Grind my gears"!
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