headhunter23 0 Posted March 25, 2009 Report Share Posted March 25, 2009 Hey mr rc-cam, are there any issues to doing this? http://www.rcgroups.com/forums/showthread.php?t=1021273 Seems to work... Quote Link to post Share on other sites
Terry 5 Posted March 25, 2009 Report Share Posted March 25, 2009 (edited) The main issues are that it will not be a propper match to the co-ax or RX and the results will be unpridictable. Oh and I forgot ther increased chance of multipath interference. Terry Edited March 25, 2009 by Terry Quote Link to post Share on other sites
Kilrah 2 Posted March 25, 2009 Report Share Posted March 25, 2009 In theory yes, ut in practice it seems to work "abnormally" well... For now I haven't been able to bring a technical argument he couldn't counteract by a "yes but it works"... To me his thing if it works should behave more like an omni in the end, but in practice it works loads better than the 3 omnis he compared to... Quote Link to post Share on other sites
Mr.RC-Cam 129 Posted March 25, 2009 Report Share Posted March 25, 2009 I'm a bit confused by what he started with and what he ended up with. It's hard to tell the full story from the photos. When I look at the photos at his web site and the forum discussion, I see that the stock antenna appears to have a PCB based half-wave dipole on one side, with a simple ground plane on the other. So, at first glance from the photos, I just don't recognize a common PCB based patch antenna at all. At this point it seems to be a simple monopole with ground plane / reflector. But then I see that there is another PCB that has a more traditional looking patch element on it (or so I think), but no coax connections to it. Ok, so the design seems to rely on the RF coupling from the half-wave element to the floating patch element. But from what I can see in the pre-mod photo, the second board with the patch-like element appears to be on the wrong side of the half-wave element (it's behind the ground plane). I think it might be an illusion from the posted photos. Or maybe the stock antenna was taken apart and then put back together in the wrong order for the photo shoot? Honestly, it is really hard to know for sure. The final construction is a bit of a mystery to me. The center board is the one with the coax feedline that drives the half-wave stripline element and the groundplane. But then this board is sandwiched between the two patch-like elements and separated by the air dielectric. One of the boards is in a place that would allow RF coupling to the half-wave driven element. But the other one is on the back side of the groundplane/reflector. There would be some RF coupling, but I can't imagine the signal strength would be very high on that side. I'm not surprised that the triple deck two headed antenna receives on both sides since I have flown on the backside of some patch antennas and obtained video signals too when the Tx was within a reasonable distance. Overall, I am not sure what advantage a non-optimized two headed patch would have over a well designed dipole whip antenna. Some measurements would really be grand (to see the technical performance). I would definitely give the project 4-stars for ingenuity, especially since the builder is happy with the results. That is all that matters. Quote Link to post Share on other sites
W3FJW-Ron 0 Posted March 25, 2009 Report Share Posted March 25, 2009 It appears to be a driven element with a patch director element rather than a single element on the front and back. Received signal strength would be rather sharp off the sides. Quote Link to post Share on other sites
Mr.RC-Cam 129 Posted March 25, 2009 Report Share Posted March 25, 2009 Or perhaps a loosely designed variation of this?: http://www.feko.info/knowledge-base/applic...ive-feed-probe/ Whatever design the unmodified antenna is using, it's not a typical PCB patch. Quote Link to post Share on other sites
W3FJW-Ron 0 Posted March 25, 2009 Report Share Posted March 25, 2009 I think I'd just as soon etch the dipole and director(?) elements on a single piece of ckt board. I suspect the results would be about the same without all the complication. Quote Link to post Share on other sites
Muppet 0 Posted March 31, 2009 Report Share Posted March 31, 2009 (edited) Hye, There's more photo and video of my antenna here: http://aeroimmersion.free.fr/DualPatchAntenna.htm There no electrical connection between the front, the rear and the central plate. The difference between with or without the rear plate is very high. The normal patch antenna as just the plate with cable and connector and the front plate. I only have ad a plate (like the front plate) symetrical opposed on the rear side. Exuse me for my bad english... Edited March 31, 2009 by Muppet Quote Link to post Share on other sites
Mr.RC-Cam 129 Posted March 31, 2009 Report Share Posted March 31, 2009 A photo on the site that I didn't notice before shows an aperature slot in the reflector (behind the driven element). It is a very unique antenna and quite unusual when compared to a typical PCB patch design. It's even more unusual after your modifications. Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.