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Jlerch

darn new guy says "Thank you", an introductin, and yea, a qu

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1st a big thank you for forum, I've been reading, building, flying, and encountering an amazing amount of success in the last 24 hours. :D

Here's a link to my "shout out" thank you video for the GP Patch antenna:

I recorded this video shortly after my first REAL FPV flight of nearly 16 minutes, and I might have been a little excited at the time of the recording.

My first attempt at FPV with stock antennas resulted in a frustratingly terrible video signal. Yesterday morning I did some searching, found this site, found the instructions, realized how 'simple' they were, built it from crud laying around in the shop, went to the field and flew it. WOW, and I still haven't done anything to the Tx ant yet, its still stock..

Here's short link to what the ground station looked like. After doing some reading this AM, I see that lowering the Rx ant may actually improve performance..

I've had some strange hobbies over the years, but this FPV stuff is the berries!

Here's a quick introduction to my last 25 years of hobbies and employment

  • Diesel Technician
  • US Army, 27H, Hawk missile launcher tech (no radar training sadly, but lots of electronics, even if there were tube based!)
  • Field Tech for large US computer company (current employment)
  • Played with speaker building for a few years. Measured speaker characteristics to determine the Thiel-Small parameters and built a lot of boxes and crossovers.
  • Played with Astronomy for a few years. My last project was a binocular build, a 120x400mm Binocular build :) Twin 16" mirrors, mounted in an powder coated aluminum frame, with servo driven tracking. Even went so far as to grind, polish, figure, the primary mirrors, built a vacuum coating system to coat the primary mirrors, and an oven to powder coat the frame work.
  • A little over a year ago, I got bit by the RC helicopter bug. Since then, I've lived and breathed RC heli's. I purchased a plane to help build orientatoin skills, and then I read about FPV somewhere, and well here I am now :)

Finally, I do have a question. This Ant -> http://www.yb2normal.com/antenna3.html

If I did my homework, based on the length is setup for 2.4ghz, yes? If I scaled it so that it was 8.2CM in length, I would end up with an Ant for 910mhz, yes?

If I decide to go with the simple dipole ant in this forum, fabricated from coax cable, does it need to be mounted vertically or horizontally, if I'm using the GP patch ant on my Rx? (I assume vertically is the the answer)

Anyway, thanks for such a great resource!

James Lerch

Parrish, Florida

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James,

You're most welcome!

Even went so far as to grind, polish, figure, the primary mirrors

Been there, done that, never doing it again, too much hassle :)

If I did my homework, based on the length is setup for 2.4ghz, yes? If I scaled it so that it was 8.2CM in length, I would end up with an Ant for 910mhz, yes?

If I decide to go with the simple dipole ant in this forum, fabricated from coax cable, does it need to be mounted vertically or horizontally, if I'm using the GP patch ant on my Rx? (I assume vertically is the the answer)

Yes and vertically.

Cheers,

Sander.

Edited by ssassen

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Excellent job for a first effort.

1. 468/freq mhz/2= 1/4 wavelength to figure out the element length. The ground plane elements should be IIRC, about 10% longer.

2. Vertically.

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Thanks guys, I got some more time on the bird today, and boy is this addicting! ;)

Let me ask one more thing that I don't understand. It is with regards to a dipole antenna fabricated from coax cable. How does peeling back the ground shield work? IE if I have 3.2 inches of center conductor exposed, and 3.2 inches of the braided shield peeled back and pulled up tight against the existing cable, how is the exposed ground shield different than the actual ground shield it overlaps?

I guess coax cable is one of those things that mystify me, which usually means I'm lacking an understanding of a key concept. My best guess is coax is kind of like a wave guide, but to be honest, wave guides messed with my head as well. :(

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how is the exposed ground shield different than the actual ground shield it overlaps?

I'm not sure what antenna project you are working on, but it sounds a lot like the one from the old rc-cam4 system (www.rc-cam.com/rc-cam4b.htm). The coaxial dipole design shown there is often called a vertical bazooka.

The reason the turtlenecked coax becomes a radiator is because the RF currents are no longer balanced. Since it is electrically isolated from the underlying coax shield, the turtlenecked conductor is a different RF current path. Long story short, the center conductor and outer shield no longer carrying 180 degree RF currents once they enter the fabricated turtlenecked and exposed elements, so the currents are not able to cancel each other out. So they radiate.

The design on the rc-cam4 antenna project worked well for me, but was not fully optimized. The turtlenecked shield should be reduced in length by the value of the coax's dielectric constant (0.66 for RG174). For your 910Mhz coaxial dipole, I suggest 8.2cm for the center element and 5.7cm for the turtlenecked shield. There's sufficient length in the center element to allow some minor trimming for best match.

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