Circularly Polarized Helical antenna 7.5 -13 dbi - New: Wave Trap match! - Page 56 - RC Groups
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May 10, 2012, 07:04 AM
New RC geek!
Hi
Can I use galvanized steel as wire around my PVC former?
Inge
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May 10, 2012, 07:06 AM
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Deleted.
Last edited by slarys; May 10, 2012 at 08:02 AM.
May 10, 2012, 09:39 AM
Engineer for Christ
IBCrazy's Avatar
Quote:
Originally Posted by Ingiskhan
Hi
Can I use galvanized steel as wire around my PVC former?
Inge
Absolutely!
May 10, 2012, 10:10 AM
Registered User
What about a single sided pcb for reflector?
May 10, 2012, 10:33 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by msev
What about a single sided pcb for reflector?
Thats what I do. The material beind the reflector does not have influence. So basically what counts is the copper cladded surface of that PCB and as such it's a very good reflector due to the fact it's copper. Any well conducting material would work though.

Markus
May 11, 2012, 03:17 PM
Fool for Christ's sake
Quote:
Originally Posted by markus123456
Thats what I do. The material beind the reflector does not have influence. So basically what counts is the copper cladded surface of that PCB and as such it's a very good reflector due to the fact it's copper. Any well conducting material would work though.

Markus
Is there much loss if I reverse the single-sided pcb so that the copper side is away from the helix? I was thinking the I could use the thickness of the pcb to produce a uniform gap between reflector and feed point in the first quarter turn.
May 11, 2012, 03:40 PM
Engineer for Christ
IBCrazy's Avatar
That will not really result in loss. However it will throw off the positioning as the dielectric of the PCb will cause a shift.

-Alex
May 13, 2012, 05:23 AM
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helix


I also use single sided pcb for reflector
May 13, 2012, 09:54 AM
Registered User
Thanks Costin!
May 13, 2012, 07:58 PM
Assault the sky
secretspy711's Avatar
the thicker the better, right? I used 1/4" OD refrigerator tubing. Will this work? This is for 1280MHz

(yes, I know it's left-handed)
May 14, 2012, 05:17 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by secretspy711
the thicker the better, right? I used 1/4" OD refrigerator tubing. Will this work? This is for 1280MHz

(yes, I know it's left-handed)
No, the thicker the more wideband. A good thickness for this frequency would be 4.6mm ~0.18". It will work though.

The more wideband - especially a helica - is, the more it picks up noise from frequency wise nearby sources. You don't want that as it stuffs the RF input stage of your receiver. I personally strive to make my helicals as narrowband as it gets for the very reason. Again, it WILL work, and unless you fly in a urban area with a high RF noise floor, you will get good results.

HTH

Markus
May 14, 2012, 10:25 AM
Assault the sky
secretspy711's Avatar
Thank you Markus. Is there any chance of damaging my receiver with this? I will try this antenna but I may look for thinner tube. .18 is optimal?
May 14, 2012, 10:37 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by secretspy711
Thank you Markus. Is there any chance of damaging my receiver with this? I will try this antenna but I may look for thinner tube. .18 is optimal?
No worries, unless you hook your antenna up to the power outlet or similar your rx won't complain. Regarding the wire thikness - no worries here too. See, this is a DIYer thread right? So if you are happy with results as you can expect from something like this you are totally totally fine. If you are after breaking the current long range record inside a city, well then the story is different.

Markus
May 15, 2012, 12:56 AM
Build Something
subsonic's Avatar
I have two questions:

o What is the ideal dimension for the centre conductor to exit the coaxial shield above the reflector? In Secretspy711’s second photo above, it looks like it exits half an inch or so above the reflector. Is this ideal?

o It is OK to drill a hole in the reflector through which to pass the coaxial feedline, directly under the start point of the coil? This would make it easy for me to place the VRX on the back of the antenna. I’d also like to drill holes for mounting other things, but I’m just wondering if drilling holes in the reflector effects things at all.

Sub
May 15, 2012, 03:19 AM
Registered FPVer :)
markus123456's Avatar
Quote:
Originally Posted by subsonic
I have two questions:

o What is the ideal dimension for the centre conductor to exit the coaxial shield above the reflector? In Secretspy711s second photo above, it looks like it exits half an inch or so above the reflector. Is this ideal?

o It is OK to drill a hole in the reflector through which to pass the coaxial feedline, directly under the start point of the coil? This would make it easy for me to place the VRX on the back of the antenna. Id also like to drill holes for mounting other things, but Im just wondering if drilling holes in the reflector effects things at all.

Sub
I start by answering your second part: It's ok to drill that hole at the feed point. Actually almost everybody does it like this. Other holes are also not problematic. In fact the reflector could be reduced to only a circularly shaped wire. I still would try to keep the number of holes small and symetircal.

To answer the first part, use this excellent online calculator.

http://jcoppens.com/ant/helix/calc.en.php

I am not sure, but I asume you refer to the distance called "a" in jc's calculator. So the link should answer your question for the frequency and helical dimension you are after.

Markus


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