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dalbert02

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Everything posted by dalbert02

  1. I started a little post on the history of FPV over at RCG. May you guys that don't frequent that site check it out and offer any corrections or additions or point out any errors. I won't be offended. Thank you. -dave http://www.rcgroups.com/forums/showthread.php?t=1585073
  2. I'd like to send my GPS coordinates from my airplane. I currently use APRS via the audio channel and a TinyTrak but I would like an alternative to get the GPS sentences into my computer/ground station. Thanks, -dave
  3. Anyone ever hear of friendcom? http://www.friendcom.com/En/pro02.htm I could only find one distributor in the US, perhaps in Europe they are more available? https://www.argentdata.com/catalog/product_info.php?products_id=107 Do you think they may be worth a gamble as a cheaper alternative to Maxstream Xtend? -Dave
  4. Any opinions on gray PVC used here and white PVC and effects on velocity factor? -dave
  5. Finally, sorry for the low quality graphic. I changed to grayscale and made it as large as I could to fit within the 250k file limitation on this board. -dave
  6. Finally, T3 is a narrow band sweep of the modified antenna. If anyone is interested, I can post the original data files and you can download the free Anritsu software so you can play with the position of the markers, plot Smith charts, or create a return loss plot. -dave
  7. Attached are the SWR plots of before and after. T1 was a wideband sweep of the original antenna.
  8. Sorry for the long delay. Sometimes there is not much activity here so I forget to check often enough. Regardless, here are some pics of IBCrazy's helix antenna. Both before and after compressing the coils. I used a sharpie to trace the original wire path and to use as a guide while compressing the coil. -dave
  9. One more I am curious about, what are your thoughts on this (if you do not mind)? http://www.trivec.com/landbased_av2055.html Obviously this would be a recieve only antenna and need to be built for your frequency. I like the idea of portability, circular polarization, and light weight. I'd love to build one for 2.5Ghz if I could find some plans on it. Thanks, -dave
  10. Thank you very much for the idea of using an attenuator. I just won a bid on a really expensive Pasternack stepped attenuator on eBay (won for only $60!) but I don't think it is rated up to 2.5Ghz. The fixed attenuators are not that expensive so I will look at those. I know Meca and MiniCircuits mentioned make descent ones. Are there any other recommended brands or brands to stay away from? Thanks, -dave
  11. Nigel, That link is awesome! Thanks! Thomas, Your link is not working. I tried searching the site but did not come up with anything. Perhaps I am over thinking this. I want a wide margin of error (+6db) for an upcoming mission. I need to fly several kilometers over ocean and can not have a video failure. Given: Rx sensitivity -80db for an acceptable picture Rx antenna +10dbi Tx +27 dbm Tx antenna 0db gain Cable loss 3db (1.5 on each side) 2510Mhz 10km Then I'll have 120db of path loss and an RSSI of -86.4dbm. http://www.distributed-wireless.com/calculators/pathloss_RSSI.html So, theoretically, I need 6.4db more just to break even and 12.4db to be within my margin of error. And if for some reason I need to go 20km? Pathloss goes to 126.4db and RSSI will be -92.4dbm, so add another 6db to the 12.4db wanted above = 18.4db. And this needs to be added to the 10db antenna I currenly have and that equals a 28.4db Rx antenna. Right? Maybe I am way off, please share your experiences, they are appreciated. -dave
  12. Thank you very much for your insight. Now on to my next question. Assuming I go with a dish antenna, I would like to calculate the expected gain for a dish of d diameter. From Wikipedia (http://en.wikipedia.org/wiki/Parabolic_antenna) I learned that the Gain G of a dish can be expressed as G = ((4 π A) / λ2) eA or G = ((π2d2) / λ2) eA Where G = Gain A = Area λ = wavelength d = diameter eA = is a "dimensionless parameter called the aperture efficiency. The aperture efficiency of typical parabolic antennas is 0.55 to 0.60." So for an example, if I look at a dish from Hyperlink (http://www.l-com.com/item.aspx?id=21730) that claims a gain of 30dbi, I get confused. Perhaps you can point out the error in my very limited math skills. G = 30dbi d = 150cm λ = 12.2449cm 30 = ((π2*1502)/12.2449 2)eA 30 = 1481 * eA eA = 0.02 very far from the .55 to .60 I expected. So where did I go wrong? I would like a 30dbi gain dish but I am unwilling to spend $429. I might be able to make one using another large dish as a mold. Does anyone know the gain of a DirecTV dish? Thank you for the continued enlightenment and education. -dave PS Happy New Year!
  13. Here is a link straight to the tutorials. Complex to Real Tutorials -dave
  14. If I had: a dish that claims 24db of gain a yagi that claims 24db of gain a patch that claims 24db of gain and they are all tuned to the same frequency, would you expect equal range out of each? Is one type of antenna any better than the other for any reason? Thank you, -dave
  15. dalbert02

    Education

    In my effort to be as smart as all of you, I have been scouring the internet for sites that help me understand complex stuff and make it real easy to understand. I humbly offer the following which was recommended to me by another non-degreed engineer. www.complextoreal.com I especially like the chapters on modulation. Anyone have some more intellectual goldmines? Thank you, -dave
  16. Any thought on egg beater antenna such as: http://on6wg.pagesperso-orange.fr/Page%201.html or Quad Helix Uplook Antenna such as: http://peakantennas.com/media/docs/QHOQHU2.pdf Thank you. -dave
  17. I'll be the first to admit I am not as smart as Patrick or OMM so please excuse this interjection into this otherwise intellegent intellectual debate. I noticed that most of the points in this article concentrated around broadcast camera backs such as NuComm's using COFDM with HDMI/SDI input. Another option, perhaps, is to look at this from the HD security camera perspective. I have used products from Firetide and Ubiquity to send HD video several miles and the latency is not bad. Perhaps it is worth a look in the search for cheap nirvana? Ubiquity bullets can be had for <$100 on ebay. -dave
  18. I recently had a very difficult time with my system. I had very poor video at less than 50 feet using a 500mW lawmate Tx and I Tri-diversity system for the Rx composed of (1) Peak Antennas Colinear and (2) HyperLink 8db circular polarized patches. After serveral days of fumbling with ferite cores, grounding, voltage isolation, filters, etc. I am embarrassed to say that only then did I swap the antenna. Although it seems obvious now, that is probably one of the first things I should have looked at. When I put the antenna on an analyzer, it had infinite SWR at my Tx frequency. Just because it worked in the past is no guarantee that it is still good. My point is, don't take anything for granted, check everything with tools or swap with a known working system. -dave
  19. The cheapest most accurate way would be to find a 'ham' in your area with a bird or coaxial dynamics wattmeter and offer to buy him a 'slug' for the frequency and power you are using. Give him the slug for payment for borrowing his meter. If you are more diy you can rectify the rf feed into a 50 ohm dummy load and measure the voltage to calculate watts. -dave
  20. Mike, I think the best way to find the optimal antenna length is to find the RSSI pin of your Rx and measure with a DVM. Use your Tx with a 50 ohm dummy load and measure the RSSI pin with varying lengths of antenna wire and ground counterpoise to get in the ball park. I would do this with the Rx actually in the plane because all the other electronics can have an effect on the tuning. Finally, for fine tuning fly your plane and use your Gecko OSD that has RSSI measurement capability and see what the the voltage is at measured distances from your Tx. If you'd like another set of hands, lets plan a day together, I'd be happy to assist! -dave
  21. Anything new on this? I'd be happy to contribute some bucks to the cause. An RC-CAM paypal site? I'm good for $20. -dave
  22. Is it possible that your pigtail may be reverse polarity SMA? Most WiFi antennas are reverse polarity SMA and most video transmitters are regular polarity SMA. Perhaps you have an 'open' cable (no center conductor contact) creating a high SWR? -dave
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