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Old May 10, 2012, 06:04 AM
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Hi
Can I use galvanized steel as wire around my PVC former?
Inge
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Old May 10, 2012, 06:06 AM
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Old May 10, 2012, 08:39 AM
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Originally Posted by Ingiskhan View Post
Hi
Can I use galvanized steel as wire around my PVC former?
Inge
Absolutely!
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Old May 10, 2012, 09:10 AM
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What about a single sided pcb for reflector?
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Old May 10, 2012, 09:33 AM
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Originally Posted by msev View Post
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
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Old May 11, 2012, 02:17 PM
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Quote:
Originally Posted by markus123456 View Post
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.
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Old May 11, 2012, 02:40 PM
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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
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Old May 13, 2012, 04:23 AM
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helix

I also use single sided pcb for reflector
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Old May 13, 2012, 08:54 AM
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Thanks Costin!
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Old May 13, 2012, 06:58 PM
Assault the sky
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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)
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Old May 14, 2012, 04:17 AM
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Originally Posted by secretspy711 View Post
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
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Old May 14, 2012, 09:25 AM
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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?
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Old May 14, 2012, 09:37 AM
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Originally Posted by secretspy711 View Post
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
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Old May 14, 2012, 11:56 PM
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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
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Old May 15, 2012, 02:19 AM
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Quote:
Originally Posted by subsonic View Post
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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