Jump to content


Photo

Antenna Projects


  • Please log in to reply
52 replies to this topic

#41 Terry

Terry

    RC-Cam Mentor

  • Trusted Member
  • PipPipPipPipPip
  • 2,079 posts
  • Gender:Male
  • Location:Bridgwater,UK
  • Interests:Aerial Photography

Posted 10 January 2011 - 08:08 AM

I made helical aerials two different ways, both on balsa wood formers. I dont know what the exact VSWR was on either as I just set them for minimum reflected power. The first one was on a rolled former and the second was made by making a copper spring and winding it on to an 1/8" balsa sheet with holes in, if you follow me? This one was a bit floppy until mounted in a tube.

I tried various ways of matching but ended up with the first 1/4 turn made from brass sheet about 5mm wide which distance to the reflector was adjusted for minimum reflected power.

I had good results but find patches easier to transport and mount.


Terry

#42 IBCrazy

IBCrazy

    RC-Cam Visitor

  • Members+
  • Pip
  • 8 posts
  • Gender:Male
  • Location:Amherst, Va

Posted 11 January 2011 - 08:30 AM

Interesting.. I might have to try that. I used a galvanized steel triangle that is 1/8 wavelength tall and 1/2 wavelength long for the first 1/2 turn. The hypotenuse of the triangle follows the helix pattern while the long leg is parallel to the reflector. Dalbert02 did some testing by compressing the coil a bit and got favorable results with the steel sheet matching stub. I wonder what cutting the center of the refletor out would do so there would be a hole as big around as the helix? Would that lower the impedance?

#43 Terry

Terry

    RC-Cam Mentor

  • Trusted Member
  • PipPipPipPipPip
  • 2,079 posts
  • Gender:Male
  • Location:Bridgwater,UK
  • Interests:Aerial Photography

Posted 11 January 2011 - 10:45 AM

Interesting idea, I know a helical with a loop reflector was posted on here by OMM but I didnt even think about how it was matched. Now I use 5.8Ghz I have given up making aerials as I have no way to test them except in the air.

Terry

Edited by Terry, 11 January 2011 - 02:21 PM.


#44 IBCrazy

IBCrazy

    RC-Cam Visitor

  • Members+
  • Pip
  • 8 posts
  • Gender:Male
  • Location:Amherst, Va

Posted 14 January 2011 - 08:04 AM

I am going to ry the series transmission line method that your described, Terry. I was looking into the ARRL handbook and it seems that to get a 50 ohm match, I need to make a strip where:

H/W = .625

I computed that from Zo = 138log(4H/d) for a single wire over infinite ground plane.

So if I keep the input feed short enough that resonation isn't a problem, I can run it a short length vertically and then run the strip 90 degrees perpendicular to it.

My question is whether the whole strip needs to be that height or if it should wind upward and finish at that height? Any idea?

-Alex

#45 Terry

Terry

    RC-Cam Mentor

  • Trusted Member
  • PipPipPipPipPip
  • 2,079 posts
  • Gender:Male
  • Location:Bridgwater,UK
  • Interests:Aerial Photography

Posted 14 January 2011 - 10:51 AM

Hi Alex, I wish I had one of my helicals to hand so I could take a pic but I think they are in the loft somewhere.

Mine both started low and got higher as they went round but not as much as the normal pitch. I dont think it is critical but I had no way to test the effects apart from the SWR. From memory the strip started very close to the reflector, probably 1mm gap, the strip was soldered to the side of the N connector pin and the tip cut off.

Hope this helps.

Terry

#46 dalbert02

dalbert02

    RC-Cam Regular

  • Trusted Member
  • PipPipPip
  • 127 posts
  • Gender:Male
  • Location:miami, fl
  • Interests:saltwater flyfishing, uavs, biking, urban exploring

Posted 28 January 2011 - 02:02 PM

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

Attached Thumbnails

  • IBC Helix Before sml.JPG
  • IBC Helix After sml.JPG


#47 dalbert02

dalbert02

    RC-Cam Regular

  • Trusted Member
  • PipPipPip
  • 127 posts
  • Gender:Male
  • Location:miami, fl
  • Interests:saltwater flyfishing, uavs, biking, urban exploring

Posted 28 January 2011 - 02:04 PM

Attached are the SWR plots of before and after. T1 was a wideband sweep of the original antenna.

Attached Thumbnails

  • IBC HELIX T1 bw.jpg


#48 dalbert02

dalbert02

    RC-Cam Regular

  • Trusted Member
  • PipPipPip
  • 127 posts
  • Gender:Male
  • Location:miami, fl
  • Interests:saltwater flyfishing, uavs, biking, urban exploring

Posted 28 January 2011 - 02:06 PM

T2 is a narrow band sweep of the original.

Attached Thumbnails

  • IBC HELIX T2 bw.jpg

Edited by dalbert02, 28 January 2011 - 02:06 PM.


#49 dalbert02

dalbert02

    RC-Cam Regular

  • Trusted Member
  • PipPipPip
  • 127 posts
  • Gender:Male
  • Location:miami, fl
  • Interests:saltwater flyfishing, uavs, biking, urban exploring

Posted 28 January 2011 - 02:09 PM

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

Attached Thumbnails

  • IBC HELIX T3 bw.jpg

Edited by dalbert02, 30 January 2011 - 08:38 PM.


#50 dalbert02

dalbert02

    RC-Cam Regular

  • Trusted Member
  • PipPipPip
  • 127 posts
  • Gender:Male
  • Location:miami, fl
  • Interests:saltwater flyfishing, uavs, biking, urban exploring

Posted 28 January 2011 - 02:11 PM

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

Edited by dalbert02, 28 January 2011 - 02:11 PM.


#51 dalbert02

dalbert02

    RC-Cam Regular

  • Trusted Member
  • PipPipPip
  • 127 posts
  • Gender:Male
  • Location:miami, fl
  • Interests:saltwater flyfishing, uavs, biking, urban exploring

Posted 28 January 2011 - 02:16 PM

Any opinions on gray PVC used here and white PVC and effects on velocity factor?
-dave

#52 IBCrazy

IBCrazy

    RC-Cam Visitor

  • Members+
  • Pip
  • 8 posts
  • Gender:Male
  • Location:Amherst, Va

Posted 07 December 2011 - 10:17 AM

Ok, this is for MR RC-CAM.

This is the Turnstile over reflector antenna he has spoken about, well, sort of. I never saw cyberFlyer's antenna. I used vector phasing to obtain a .98 axial ratio without any kind of phasing system to match it other than the reactive vectors of round wire. The reflector was the killer. That's where Hugo came in. Hugeone helped me in modeling this one and tweaked it to perfection since I couldn't seem to simulate the ground plane properly.

The cool thing about this antenna: you can adjust the gain for between 5 and 10 dbic. I only have it perfected for 9.5dbic. I was hoping to get 5 dbic, actually, but... well... I'm happy with this. Will work on the 5dbic one later.

As always, tutorials will be published.

@RC-CAM - If you want the details early, Email me :)

-Alex

Attached Thumbnails

  • Crosshair smaller.jpg


#53 Mr.RC-Cam

Mr.RC-Cam

    RC-Cam Mentor

  • Admin
  • PipPipPipPipPip
  • 4,654 posts
  • Location:USA
  • Interests:R/C video and photography.

Posted 07 December 2011 - 02:19 PM

Very nice. It's awesome to see the circular polarized antenna building activity. A couple years ago you could probably count the FPV'ers rolling their own on one hand. :)
- Thomas